A blind H I survey in the Ursa Major region€¦ · The Ursa Major cluster is smaller – Tully et...

MNRAS (2012) doi:10.1093/mnras/sts160

A blind H I survey in the Ursa Major region�

K. Wolfinger,1,2† V. A. Kilborn,1 B. S. Koribalski,2 R. F. Minchin,3 P. J. Boyce,4

M. J. Disney,5 R. H. Lang5 and C. A. Jordan6

1Centre for Astrophysics & Supercomputing, Swinburne University of Technology, Mail H39, PO Box 218, Hawthorn, VIC 3122, Australia2CSIRO Astronomy and Space Science, PO Box 76, Epping, NSW 1710, Australia3Arecibo Observatory, HC03 Box 53995, Arecibo, PR 00612, USA4Registry, Cardiff University, Cardiff CF10 3UA5School of Physics and Astronomy, Cardiff University, Cardiff CF24 3YB6Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL

Accepted 2012 October 4. Received 2012 September 30; in original form 2012 January 31

ABSTRACTWe have conducted the first blind H I survey covering 480 deg2 and a heliocentric velocityrange from 300 to 1900 km s−1 to investigate the H I content of the nearby spiral-rich UrsaMajor region and to look for previously uncatalogued gas-rich objects. Here we present thecatalogue of H I sources. The H I data were obtained with the four-beam receiver mountedon the 76.2-m Lovell telescope [full width at half-maximum (FWHM) 12 arcmin] at theJodrell Bank Observatory (UK) as part of the H I Jodrell All Sky Survey (HIJASS). We usethe automated source finder DUCHAMP and identify 166 H I sources in the data cubes with H I

masses in the range of 107–1010.5 M�. Our Ursa Major H I catalogue includes 10 first-timedetections in the 21-cm emission line.

We identify optical counterparts for 165 H I sources (99 per cent). For 54 H I sources(∼33 per cent) we find numerous optical counterparts in the HIJASS beam, indicating ahigh density of galaxies and likely tidal interactions. Four of these H I systems are discussedin detail.

We find only one H I source (1 per cent) without a visible optical counterpart out of the 166H I detections. Green Bank Telescope (FWHM 9 arcmin) follow-up observations confirmedthis H I source and its H I properties. The nature of this detection is discussed and comparedto similar sources in other H I surveys.

Key words: catalogues – surveys – galaxies: fundamental parameters.

1 IN T RO D U C T I O N

The distribution of galaxies in the Universe is not uniform – galaxiesare found in filamentary structures, groups and clusters (e.g. Collesset al. 2001). The observed ‘cosmic web’ structure is in good agree-ment with numerical simulations according to cold dark matter cos-mology (e.g. Springel et al. 2005; Simon & Geha 2007), wherebygravity drives the formation of structure from small, primordial,Gaussian fluctuations. Dark matter haloes grow through mergingand accretion of smaller ones. Within the dark matter haloes, galax-ies form by cooling of baryons (e.g. White & Rees 1978). Hence,small dark matter haloes are the primordial building blocks of largerstructures in the hierarchical model of structure formation.

Dwarf irregular galaxies with low stellar luminosity and low sur-face brightness galaxies are typically discovered in neutral hydrogen

� The data cubes were obtained with the Lovell telescope at the Jodrell BankObservatory, UK.†E-mail: [email protected]

(H I) surveys (Schombert et al. 1992, Minchin et al. 2003, Giovanelliet al. 2005), as they are rich in neutral gas but difficult to detect inoptical or infrared surveys. Whilst optical surveys are most sensi-tive to high surface brightness early-type galaxies (Disney 1976),H I surveys are unbiased by stellar populations and are most likelyto detect gas-rich late-type spirals and irregular galaxies. Henceoptical and H I surveys complement each other as there is a roughcorrelation between increasing H I content from early- to late-typegalaxies and decreasing optical surface brightness with morpho-logical type (Toribio et al. 2011). Discoveries in H I surveys alsoinclude intriguing objects, e.g. the detection of an H I massive cloudwithout stellar counterpart, within the NGC 2442 group (Ryderet al. 2001), extended H I arms or tidal tails (Koribalski & Lopez-Sanchez 2009) and H I between galaxies in groups (Koribalski &Manthey 2005, Kilborn et al. 2006, English et al. 2010). Large-areablind H I surveys have been conducted such as the Arecibo H I StripSurvey (AHISS; Zwaan et al. 1997), the Arecibo Dual Beam Sur-vey (ADBS; Rosenberg & Schneider 2000), the H I Jodrell All SkySurvey (HIJASS; Lang et al. 2003), the H I Parkes All Sky Survey(HIPASS; Staveley-Smith et al. 1996, Barnes et al. 2001; Koribalski

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et al. 2004, Meyer et al. 2004), the Arecibo Legacy Fast ALFA sur-vey (ALFALFA; Giovanelli et al. 2005) and the Arecibo GalaxyEnvironment Survey (AGES; Auld et al. 2006). Upcoming H I sur-veys such as the ASKAP H I All-Sky Survey (known as WALLABY;Koribalski & Staveley-Smith 20091) will further contribute to ourknowledge of gas-rich galaxies in the local Universe.

Isolated galaxies tend to have noticeably different properties fromgalaxies residing in dense regions. Observations have shown thatearly-type galaxies are common in clusters whereas late-type galax-ies dominate the less dense environments (morphology–density re-lation; e.g. Dressler 1980). The importance of environment andthe idea of transformation of galaxies in dense environments arosewhen Butcher & Oemler (1978) discovered that galaxy clusters athigher redshift contain a population of blue galaxies which nearbygalaxy cluster counterparts are missing. However, it is still a mat-ter of debate as to which properties correlate with the decrease ofblue galaxies from high- to low-redshift galaxy clusters, e.g. X-rayluminosity (Andreon & Ettori 1999; Fairley et al. 2002), richness(Margoniner et al. 2001; De Propris et al. 2004), cluster concentra-tion (Butcher & Oemler 1984; De Propris et al. 2004), presence ofsubstructure (Metevier, Romer & Ulmer 2000) and cluster velocitydispersion (De Propris et al. 2004). Lewis et al. (2002) and Gomezet al. (2003) discuss the correlation between star formation rate andlocal projected density. The authors find low star formation rates at2–3 virial cluster radii – which is equivalent to poor galaxy groupdensities. Therefore, galaxies may be preprocessed in groups, asphysical processes in the studied clusters cannot solely account forthe observed variations in galaxy properties. Galaxy transformationas a smooth function of environment is also suggested by Cappellariet al. (2011) in terms of a kinematic morphology–density relation,i.e. separation into fast and slow rotators.

There have been a number of studies on the effect of environmenton the H I content of galaxies in clusters (e.g. Giovanelli & Haynes1985, Solanes et al. 2001, Gavazzi et al. 2005, Chung et al. 2009),and loose groups (e.g. Kilborn et al. 2005; Omar & Dwarakanath2005). Through observations of isolated galaxies, we can define theexpected H I mass in normal spiral galaxies of a particular linearoptical diameter and morphological type. In dense regions, such asclusters, there is often an H I deficiency observed, indicating that H I

gas is removed from galaxies in these environments (e.g. Solaneset al. 2001). Recent observations have found a similar H I deficiencyin the less dense group environments (Omar & Dwarakanath 2005,Kilborn et al. 2009) indicating that the spirals may begin to losetheir H I reservoir well before reaching the dense centre of a cluster.

An ideal target to study the effect of environment on the evolu-tion of gas-rich galaxies is the nearby Ursa Major cluster and itssurroundings as most of the known member galaxies are late-typegalaxies. The Ursa Major cluster is quite different in its nature com-pared to the well-known and similarly distant Virgo and Fornaxclusters. Generally clusters are composed of hundreds of gas-poorearly-type galaxies clustered around a central larger elliptical (e.g.Dressler 1980). The Ursa Major cluster is smaller – Tully et al.(1996) identified 79 high-probability cluster members. The clusteris essentially composed of late-type galaxies, in particular spiralgalaxies with normal gas content, that are not centrally concen-trated (Tully et al. 1996). This lack of a concentration towards anycore and the overlap with many groups nearby the cluster mightexplain why the Ursa Major cluster is less studied compared tothe Virgo and Fornax clusters. The several groups nearby the Ursa

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Major cluster make studying its dynamics a complex problem andthe cluster difficult to define (Appleton & Davies 1982, Tully et al.1996). However, Tully et al. (1996) define the cluster members to liewithin a projected 7.◦5 circle centred at α = 11h56.m9, δ = +49◦22′

and with heliocentric velocities between 700 and 1210 km s−1.The cluster lies at a distance of 17.1 Mpc (Tully et al. 2008).

The few previous studies of the Ursa Major cluster have found thatit has a low velocity dispersion of only 148 km s−1, a virial radiusof 880 kpc (Tully et al. 1996) and no X-ray-emitting intraclustergas has yet been detected (Verheijen & Sancisi 2001). The UrsaMajor cluster has a total mass of 4.4 × 1013 M� (Tully 1987) anda B-band absolute luminosity of 5.5 × 1011 L� (Tully et al. 2008).Compared to the Virgo cluster this is about 30 per cent of its lightbut only 5 per cent of its mass (Tully 1987; Tully et al. 2008). Thenumber of H I-rich galaxies in Ursa Major is comparable to those inVirgo (Tully et al. 1996) and the Ursa Major cluster almost meetsthe Abell richness 0 standard. To qualify as an Abell richness class0 the criteria are (i) 30 galaxies in B or (ii) 26 in R within 2 mag ofthe third brightest galaxy. The Ursa Major cluster is slightly short –29 galaxies in B and 25 in R (Tully et al. 1996). Besides Ursa Major,only the Virgo cluster has such a high abundance of H I-rich galaxieson a 2 Mpc scale in the nearby Universe (cz < 3000 km s−1) (Tullyet al. 1996).

Zwaan, Verheijen & Briggs (1999) note that the mostly late-type galaxies in the Ursa Major cluster do not seem to be seriouslyaffected by tidal interactions indicating that the system is in an earlyevolutionary state. However, Verheijen & Sancisi (2001) studied 43spiral galaxies in detail and found 10 interacting systems that showdistorted morphologies and tidal debris. There is a deficiency ofknown dwarf galaxies in the Ursa Major cluster – there are onlytwo dozen dwarfs, whereas up to 103 could be expected to be foundif the same steep luminosity function claimed for Virgo was validfor the Ursa Major cluster (Trentham, Tully & Verheijen 2001). Todate, (i) the small number of dwarf galaxies, (ii) the low velocitydispersion, (iii) the non-detection of X-ray-emitting intracluster gas,(iv) the low abundance of elliptical galaxies in the cluster and (v)the total mass <1014 M� challenge the question ‘why not call it agroup?’. Clusters usually have a broader velocity distribution, a hotintracluster gas which can strip the galaxies off their H I gas and anenhanced population of both the early-type (S0 and E) galaxies andthe H I-depleted spiral galaxies. As the majority of the Ursa Majormembers are H I-rich spiral galaxies such as those one finds in thefield, the distinction between the ‘Ursa Major cluster’ as opposedto an ‘Ursa Major group’ is not clear. One hypothesis is that UrsaMajor is a newly forming cluster given that the estimated crossingtime is approximately half a Hubble time, in contrast to Virgo andFornax where the crossing times are 0.08 and 0.07 H−1

0 , respectively(Tully et al. 1996).

In this paper we present the catalogue of H I sources as detectedin the first blind H I survey of the Ursa Major region (approximately480 deg2). The analysed region overlaps with the Canes Venaticiregion for which Kovac, Oosterloo & van der Hulst (2009) haveconducted a deep blind H I survey (H I mass sensitivity ∼106 M�)using the Westerbork Synthesis Radio Telescope (WSRT) in an areaof 86 deg2 (vsys ≤ 1330 km s−1). Our H I data were obtained as partof the HIJASS. The data acquisition and determination of the H I

sources are described in Section 2 including a discussion of thecatalogue completeness and reliability. The H I properties of thesources are presented in a catalogue in Section 3. The H I mass limitof the presented catalogue is 2.5× 108 M� assuming a velocitywidth of 100 km s−1 and a distance of 17.1 Mpc. First, results andbasic property distributions of the HIJASS sources are presented in

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A blind H I survey in the Ursa Major region 3

Section 4. Furthermore, we identify galaxy pairs/systems that arehigh-probability candidates for galaxy–galaxy interactions and dis-cuss four systems in detail, two of which show strikingly extendedH I content.

In a forthcoming paper we will investigate the nature of theUrsa Major cluster/group and probe the hypothesis that it is a newlyforming cluster. We will study substructures and their dynamics, andpresent dynamical masses, total mass-to-light ratios, etc. for bothindividual galaxies and the subregions. Furthermore, to investigatethe H I properties of galaxies residing in different density regions, wewill analyse the H I sources in the Ursa Major cluster and comparethem to galaxies residing in foreground groups and the less densefilament connecting the Ursa Major with the Virgo cluster, whichlies south of Canes Venatici.

2 O B S E RVAT I O N S A N D DATA A NA LY S I S

2.1 Data acquisition and processing

The H I data cubes analysed in this paper were obtained in 2001–2002 as part of the HIJASS (Lang et al. 2003). The blind H I surveywas conducted using the four-beam receiver mounted on the 76.2-mLovell telescope at Jodrell Bank Observatory, UK. HIJASS coveredmore than 1000 deg2 in the northern sky (δ ≥ +22◦) complementaryto (i) the HIPASS which surveyed the entire southern sky (δ ≤ +2◦)from 1997 to 2000 (Staveley-Smith et al. 1996; Barnes et al. 2001;Koribalski et al. 2004) and (ii) the northern extension to HIPASS(+2◦ ≤ δ ≤ +25◦30′) carried out in 2000 to 2002 (Wong et al.2006). HIJASS provides the first blind H I survey of the nearby UrsaMajor cluster and its surroundings. To investigate the Ursa Majorregion we only consider velocities in the range 300–1900 km s−1

(all velocities are given in the optical convention cz). Sources withsystemic velocities below 300 km s−1 are excluded to minimizeconfusion with high-velocity clouds and Galactic emission – anexception are 15 obviously real galaxies with systemic velocitiesbetween 150 and 300 km s−1 that are included in the catalogue. Wenote that HIJASS data suffer from a broad-band of radio-frequencyinterference between 4500 and 7500 km s−1 (Lang et al. 2003),which lies outside our studied velocity range.

The Ursa Major region is covered by seven HIJASS data cubesmeasuring 8◦ × 8◦ and one HIJASS cube measuring 5◦ × 8◦ insize (the sky coverage is approximately 480 deg2). The cubes spana range in right ascension (RA) between 10h45m and 13h04m anda range in declination (Dec.) between 22◦ and 54◦. We note thatthe analysed region overlaps with the Canes Venatici region forwhich Kovac et al. (2009) have conducted a deep blind H I surveyin an area of 86 deg2 (vsys ≤ 1330 km s−1). The HIJASS cubes havea spatial pixel size of 4 × 4 arcmin2. In the third dimension, thechannel spacing is 62.5 kHz which corresponds to an increment of13.2 km s−1 at the rest frequency of H I. The velocity resolution is18 km s−1 after smoothing to reduce ‘ringing’ caused by Galacticemission (applying 25 per cent Tukey filter). The root mean square(rms) noise level in the analysed data is 12–14 mJy beam−1. Tominimize edge effects the overlapping HIJASS data cubes are mo-saicked to one megacube. For further information on data reduction,the Lovell telescope and HIJASS, see Lang et al. (2003).

The angular resolution of the Lovell telescope at 1.4 GHz is12.0 arcmin (Lang et al. 2003). The gridding process (using similarparameters as for HIPASS) slightly degrades the angular resolu-tion (see Barnes et al. 2001). According to Barnes et al. (2001) theresultant beam size is not well defined and depends on smoothing ra-dius, pixel size, source position, shape and strength (signal-to-noise

Table 1. The peak and integrated correction factors (fp and fint)for extended sources as a function of FWHM (x).

f(x) = a3x3 + a2x2 + a1x + a0

Coefficient fp(x) fint(x)

a3 −4.78 × 10−6 7.12 × 10−6

a2 5.54 × 10−4 −2.27 × 10−4

a1 −2.26 × 10−2 1.05 × 10−2

a0 1.112 1.003

ratio) as the gridding is a non-linear process. One can only assessthe gridded beam size by analysing simulations and synthetic sourceinjections. To determine the gridded beam size, we inject syntheticpoint sources into the raw data and measure their properties afterthe gridding process. We determine the full width at half-maximum(FWHM) beamwidth of a two-dimensional Gaussian fit to the syn-thetic sources, analogous to Barnes et al. (2001). The measuredbeamwidths vary as a function of source peak brightness (in Jybeam−1, which corresponds to Jy for point sources). Given a widerange of peak flux densities in the presented catalogue – the major-ity of sources have 33 ≤ Sp ≤ 300 mJy and a few strong sourcesrange to 3.5 Jy in peak flux density – we determine two appropriatebeamwidths: (i) 13.1 ± 0.9 arcmin for the majority of sources withSp ≤ 300 mJy and (ii) 12.4 ± 0.6 arcmin for sources with Sp >

300 mJy.The peak and integrated fluxes of point sources are preserved

during the gridding process but for extended sources, the peak andintegrated fluxes require a correction: we calculated the correctionfactors by similarly injecting synthetic extended sources into theraw data and measure their properties after the gridding process(analogous to Barnes et al. 2001). The correction factors for ex-tended sources as a function of FWHM are given in Table 1. Weobtain this function by fitting a third-order polynomial to the me-dian data points (with R2 of 99.9 per cent). In our catalogue (Section3.2), we quote both the measured and corrected fluxes for extendedsources.

2.2 Data analysis using DUCHAMP

We use the automated source finder DUCHAMP-1.1.8 (Whiting 2012)2

on the H I data cube to compile our initial candidate galaxy list.DUCHAMP is based on a threshold method and searches for groupsof adjacent pixels in position and velocity that are above the giventhreshold, which is estimated from the cube statistics (in Jy beam−1)or alternatively specified from the user as a peak flux density value.Furthermore, the user can (i) reduce the noise prior to the searchingvia wavelet reconstruction and/or smoothing (spatial or spectral)and (ii) control various parameters such as the minimum extent ofthe detections in pixels and/or channels. DUCHAMP provides a list ofthe H I detections and their properties, the H I spectra and integratedH I intensity maps (moment zero). The DUCHAMP outputs need to beinspected carefully as H I sources are occasionally merged. We canidentify such sources by eye and separate them when they do notoverlap both spatially and spectrally.

We made a comprehensive test of various input parameters andmethods to facilitate DUCHAMP detections of low peak flux and ex-tended H I sources without disproportionally increasing noise detec-tions (see Sections 2.3 and 2.5). We first apply a spectral Hanning

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smoothing to the HIJASS data and then reconstruct them with the‘a trous’ wavelet method. Hanning smoothing correlates neigh-bouring pixels in the spectral domain and determines the weightedaverage flux over a certain number of channels – the channel spac-ing remains 13.2 km s−1. We determine that the optimal Hanningsmoothing width for the data is seven channels (see Section 2.3).The wavelet method reconstructs each spectrum separately and wechose the following criteria when compiling the DUCHAMP detec-tion list: (i) the detection must be contiguous in two channels and(ii) the peak flux density of the candidate galaxies must be above16 mJy. This is an approximate 2.5σ peak flux density thresholdas the mean noise level in the smoothed and reconstructed cube is∼6.6 mJy beam−1.

In this paper, we only consider 5σ detections in peak flux in theedge-masked HIJASS megacube to present a reliable and completecatalogue of H I sources in the Ursa Major region within 300–1900 km s−1. This corresponds to a minimum in peak flux density of33 mJy and an H I mass limit of 2.5 × 108 M� (assuming a velocitywidth of 100 km s−1 and a distance of 17.1 Mpc). These selectioncriteria lead to a DUCHAMP detection list with 140 candidate galaxiesincluding merged detections (doubles to quads) that are labelled inSection 3.2.

2.3 Catalogue reliability – negative troughs

To test the reliability of the 5σ peak flux DUCHAMP detection list,we investigate the negative troughs in the edge-masked HIJASScube. When using the selection criteria as discussed in Section2.2, we identify 25 negative troughs with Sp ≤ −33 mJy and w50 ≥26.4 km s−1. All 25 negative troughs can be associated with negativebandpass sidelobes, i.e. an artefact of bandpass removal which isapparent north and south of strong H I sources (see e.g. Barnes et al.2001). This lack of negative detections (noise peaks) indicates thatthe positive DUCHAMP candidate galaxy list with Sp ≥ 33 mJy andw50 ≥ 26.4 km s−1contains high-probability real H I sources.

Hanning smoothing is known to enhance the brightness of sources– on the scale of the smoothing width – with respect to the noisein each channel map, but reduces the peak strength (signal-to-noiseratio) of sources on other scales. Whiting (2012) shows that anappropriately chosen smoothing width can still increase the recov-ery rate of sources on different scales than the smoothing widthas the noise level is suppressed. However, to prevent loss of infor-mation on different scales, we also use the wavelet reconstructionto further suppress the noise and to enhance structures on variousscales (narrow and broad profiles). Using wavelet reconstructionalso suppresses noise peaks, baseline ripples or radio-frequency in-terferences as discussed in Westmeier, Popping & Serra (2012). Forfurther information on DUCHAMP and the noise suppression methodssee Whiting (2012).

Some restrictions on spatial and spectral extent of DUCHAMP detec-tions greatly improve the reliability, such as the applied minimumnumber of channels (≥2) in which the detection must be contigu-ous (Whiting 2012). The selection criteria as listed in Section 2.2are chosen to limit the number of false detections and to present areliable catalogue of H I sources in the Ursa Major region in thispaper.

2.4 Catalogue reliability – follow-up observations

The reliability of the catalogue is increased by follow-up observa-tions and rejection of unconfirmed sources from the catalogue. Were-observed 17 apparent first-time detections in HIJASS with the

Green Bank Telescope (GBT; FWHM 9 arcmin) – nine of whichhave an associate optical counterpart that match in position andvelocity to the H I detection and eight candidate galaxies/H I cloudswithout a previously catalogued optical counterpart. The rms noiselevel is between 4 and 7 mJy for H I sources with an associate opticalcounterpart and approximately 3 mJy for the candidate galaxies/H I

clouds. Given that the lowest peak flux density of the candidategalaxies/H I clouds is 33 mJy, this will lead to signal-to-noise ra-tio detections >10. The velocity resolution of the GBT data is3.3 km s−1 after boxcar smoothing.

The GBT follow-up observations confirmed all nine H I sourceswith an associate optical counterpart. However, only one out ofthe eight candidate galaxies/H I clouds was confirmed, namelyHIJASS J1219+46. Therefore, seven initial DUCHAMP detections areexcluded from the presented catalogue in this paper. Inspecting theoriginal as well as the smoothed and reconstructed data cubes byeye reveal that the unconfirmed detections are noise peaks on topof large-scale baseline ripples. DUCHAMP provides an option ‘flagbaseline’ which removes the baseline from each spectrum prior tocompiling the detection list. However, we did not utilize this optionas not only does it remove all candidate galaxies/H I clouds fromthe detection list, some of the faint H I detections with an associateoptical counterpart were not included as well.

2.5 Catalogue completeness – synthetic source injection

To measure the catalogue completeness we insert numerous syn-thetic point sources into the eight HIJASS cubes, prior to run-ning DUCHAMP. The rate at which the synthetic sources are recov-ered reflects the completeness, as discussed explicitly in Zwaanet al. (2004) (also see Wong et al. 2006). The criteria for a recov-ered synthetic source are a DUCHAMP detection within 10 arcminand 200 km s−1 of the original position and velocity of the syn-thetic source (the average position and velocity accuracies for H I

sources with peak flux densities below 100 mJy are ∼1.2 arcminand ∼14 km s−1, respectively).

The synthetic point sources are given a Gaussian spectral shapeand have random positions, 50 per cent velocity widths and peakflux densities (Kilborn et al. 2009). The 50 per cent velocity widthsare w50 ≤ 500 km s−1 and the peak flux densities are Sp ≤ 100 mJy.The synthetic sources are placed away from the noisy edges of thedata cube and are not placed on top of other sources either syntheticor real (the positions of the real sources are according to an initialDUCHAMP output list).

A total of 2000 synthetic sources are inserted into each HIJASSdata cube to obtain the DUCHAMP completeness. For a representativeHIJASS cube the completeness is shown in Fig. 1. We use naturalneighbour interpolation to achieve the grey-scale representation ofthe completeness depending on Sp and w50 or Sp and integrated fluxSint (which is a combination of both Sp and w50).

To measure the catalogue completeness as a function of one pa-rameter only – Sp, w50 or Sint – we integrate along the other variableof the completeness as discussed in Zwaan et al. (2004). We in-tegrate above the DUCHAMP selection parameters which are w50 =26.4 km s−1 and Sp = 16 mJy. These values mark the DUCHAMP de-tection limit in the smoothed and reconstructed cube – below thesevalues the completeness drops to zero. Fig. 2 shows this differentialcompleteness (circles) as well as the cumulative (crosses) com-pleteness as defined by Zwaan et al. (2004). Fig. 2 also shows theerror function fit to the data to determine the 95 per cent confidencelevels which lie at Sp = 33 mJy and Sint = 2.63 Jy km s−1. The99 per cent completeness levels are achieved at Sp = 45 mJy and

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Figure 1. The DUCHAMP completeness in a representative HIJASS cube as a function of Sp and w50 (left) and as a function of Sp and Sint (right). The brightercolours correspond to high completeness levels and the contour lines show the 99, 75 and 50 per cent completeness levels.

Figure 2. The DUCHAMP completeness as a function of Sp, w50 and Sint. The differential completeness is marked with circles whereas the cumulativecompleteness is marked with crosses. The solid lines are the error function fits to the data.

Sint = 3.55 Jy km s−1. Therefore, the peak flux density limited cat-alogue (at 33 mJy) presented in Section 3 is 95 per cent complete.

2.6 Catalogue completeness – literature comparison

As an additional measure of completeness we compare our results(Section 3.2) to an overlapping deep blind H I survey in the CanesVenatici region using WSRT (area of 86 deg2, vsys ≤ 1330 km s−1

with an H I mass sensitivity of ∼106 M�; Kovac et al. 2009). Wefind that our presented catalogue contains all but one H I sources inthe velocity range 300–1330 km s−1, with Sp ≥ 33 mJy and Sint ≥2.63 Jy km s−1 (95 per cent completeness level) as listed in Kovacet al. (2009) – the exception is NGC 4460 (vLG = 542 km s−1)with Sp = 41 mJy and Sint = 4.30 Jy km s−1 (Kovac et al. 2009).We investigated the HIJASS data cube (by eye) and identify NGC4460 at the end of negative bandpass sidelobes emerging fromthe strong double source NGC 4490/NGC 4485. NGC 4460 hasreduced peak brightness (Sp 31 mJy beam−1) due to the negativebandpass sidelobes, which prevents this H I source to be listed inour catalogue. We conclude that negative bandpass sidelobes maycause a deficit in completeness for sources with 16 ≤ Sp ≤ 45 mJyand w50 ≤ 100 km s−1 (see Fig. 1), as their peak flux densities may

lie below the detection threshold. However, this is a small effect,given the little area affected by negative bandpass sidelobes.

3 TH E H I C ATA L O G U E

3.1 Parametrization

The sources found using DUCHAMP are parametrized with an inter-active script utilizing the MIRIAD software package (Sault, Teuben &Wright 1995). The parametrization is necessary as DUCHAMP givesinitial values – dealing with double detections and obtaining re-liable H I parameters require user input. Our method is similar toLang et al. (2003) and Koribalski et al. (2004) and this will be brieflydescribed in the following section.

A spatially integrated spectrum is generated from the originalHIJASS cube, using the DUCHAMP output parameters for each source(RA, Dec., velocity, velocity widths). The spectral extent of the H I

source (velocity range) can be adjusted as necessary. An integratedH I intensity map over this velocity range is generated using theMIRIAD task MOMENT. Given a specified fitting area (in relation tothe source size), IMFIT is used to determine the central position of theH I source by fitting a two-dimensional Gaussian to the integratedH I intensity map. The obtained central coordinates are used to

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generate a new spatially integrated spectrum weighted according tothe extent of the H I source (see below). In general, we fit and subtracta first-order baseline fit to the spectrum (higher order baseline fitsare labelled in the catalogue). The H I parameters such as peak andintegrated flux, the velocity widths, the clipped rms noise and thesystemic velocity are measured using MBSPECT. In the catalogue wequote the integrated flux measured with the robust moments, the 20and 50 per cent velocity widths calculated from the width maximizerand the systemic velocity as the centre of the 20 per cent velocitywidth (see Meyer et al. 2004 for definitions).

An H I source can be unresolved or extended with respect tothe gridded beam size. To identify point and extended sources,we compare the integrated flux measurements obtained from (i)spectra where every pixel is weighted according to the expectedbeam response (beam-weighted as for point sources) to (ii) spectrawhere the flux is directly summed (as for extended sources). Theconsidered area is given by a box surrounding the central position,e.g. of size 5 × 5 and 7 × 7 pixel2 that correspond to 20 × 20and 28 × 28 arcmin2, respectively. A potentially extended sourceis identified due to an increase in the integrated flux from a beam-weighted spectrum to a summed spectrum in a bigger box. Thisincrease can also occur due to confusion with a nearby H I sourcewhich might be included in the bigger box – such sources are flaggedas double sources (d) in the catalogue and are parametrized bygenerating a beam-weighted spectrum as for point sources. Trulyextended sources (e), which are indicated by an increase in theintegrated flux, are confirmed by investigating the residual map ofthe Gaussian fit. An extended source will show flux in the residualmap whereas a point source is well described by the Gaussian fit.

3.2 The H I catalogue

The DUCHAMP detection list in the smoothed and reconstructedHIJASS megacube contains 140 candidate galaxies with systemicvelocities between 300 and 1900 km s−1. After the parametrizationprocess, four galaxies have systemic velocities below 300 km s−1.In addition, we identified 11 H I sources with systemic velocitiesbetween 150 and 300 km s−1 that are included in the sample asthey are obviously real galaxies as opposed to Galactic emissionor high-velocity clouds. However, H I sources with systemic veloc-ities below 300 km s−1 are not included in Section 4. Furthermore,we identified several double, triple and quad detections that areseparated during the parametrization process leading to a total of173 H I sources that are parametrized from the original HIJASSmegacube. We exclude seven detections from the presented cat-alogue that are unconfirmed in GBT follow-up observations (seeSection 2.4). Therefore, a total of 166 H I sources are listed in ourcatalogue in Section 3.2.

The parametrized H I sources are cross-correlated with galaxieslisted in the NASA/IPAC Extragalactic Database (NED; as of 2012September) and the Sloan Digital Sky Survey Data Release 8 (SDSSDR8). We only consider galaxies with cross-identifications in NEDand galaxies with spectroscopic redshifts with confidence levelszconf > 0.95 in SDSS as possible counterparts. We associate an H I

source with a catalogued galaxy, if this galaxy is within the griddedbeam size (or within the extent of the H I intensity contours for largesources) and within the velocity range of the H I source. We find54 H I sources that have multiple candidate counterparts. These arepotentially confused H I sources and may be interacting systems.To determine the most likely optical counterpart (listed in the firstrow of the catalogue), the H I position uncertainty, the heliocentric

velocity, the optical galaxy size (in relation to the H I mass and size)and the morphology are considered.

We find only one out of the 166 catalogued H I sources thatdoes not have an associate optical counterpart listed in NED/SDSSor visible on Palomar Digitized Sky Survey (DSS) images. Thiscandidate galaxy/H I cloud – HIJASS J1219+46 – is discussed inSection 3.4.

Table 2 lists the H I sources and their optical counterparts as fol-lows: column (A1) gives the HIJASS name; columns (A2)–(A4) listthe central H I position [RA (J2000), Dec. (J2000)] and its uncer-tainty σ pos (all uncertainties are discussed in Section 3.3); column(A5) contains the systemic velocity (km s−1) with its uncertaintyσ v; column (A6) states ‘ID’ for H I detections that have an opticalidentification and ‘PUO’ for the previously uncatalogued gas-richobject; columns (A7)–(A10) list the details of the optical counter-parts, i.e. name, RA (J2000), Dec. (J2000) and heliocentric velocity(km s−1); columns (A11) and (A12) give the angular separation(arcmin) and velocity offset (km s−1) from the H I parameters. Themost likely optical counterpart is given in the first row and galaxiesthat lie within the gridded beam or within the extent of the H I inten-sity contours (for large sources) and might confuse the H I contentare quoted in the subsequent rows.

The measured H I properties of the HIJASS detections are givenin Table 3. The columns are as follows: column (B1) gives the HI-JASS name; columns (B2)–(B4) gives the measured and correctedpeak flux densities (Sp) with its uncertainty (in Jy); columns (B5)–(B7) list the measured and corrected integrated flux (Sint) with itsuncertainty (in Jy km s−1); columns (B8) and (B9) contain the ve-locity widths at 50 and 20 per cent of the peak flux density with theiruncertainties (in km s−1); column (B10) gives the clipped rms mea-sured in MBSPECT; column (B11) lists the distance to the galaxy (inMpc) as obtained from the Extragalactic Distance Database (EDD;Tully et al. 2009 – only distances obtained from colour–magnitudediagrams, tip of the red giant branch and other high-quality meth-ods are considered) or calculated from the Local Group velocity(see Koribalski et al. 2004 for HIPASS) – we adopt H0 =70 km s−1 Mpc−1; for galaxies within the cluster definition by Tullyet al. (1996) we adopt a distance of 17.1 Mpc; column (B11) givesthe logarithm of the H I mass and column (B12) contains flags for 78extended (e) and 54 confused (c) H I sources, 38 H I sources whichare part of DUCHAMP double detections (d), 10 H I sources withouta central position from a position fit (f) and therefore without ma-jor/minor axis measurements, 10 H I sources lying nearby negativebandpass sidelobes (b), 10 newly detected H I sources in the 21-cmemission line (n), 15 H I sources with systemic velocities below300 km S−1 (v), 34 sources where independent distance measure-ments are available (i) and numbers to indicate higher order baselinefits. The H I mass in column (B11) is calculated from the integratedflux [Sint and Sint(corr) for extended sources, respectively] accordingto MH I = 2.356 × 105 × D2 × S int (M�) with distances as givenin column (10). We note that Kovac et al. (2009) also determineadequate distances in the Local Group frame, neglecting peculiarvelocities (using Yahil, Tammann & Sandage 1977).

We show a velocity integrated H I map with symbols marking theprojected positions of all parametrized H I sources in this cataloguein Fig. 3. H I sources with an associated optical counterpart aremarked with open ellipses whereas the previously uncatalogued H I

source is marked with a filled ellipse (black). Furthermore, previ-ously catalogued sources that are newly detected in H I are markedwith crosses. The size of the ellipses indicate the measured ma-jor axis – ellipses surrounded by boxes mark H I detections forwhich no central position and no extent (major and minor axis) is

at Swinburne U




ownloaded from



Tabl

e2.

The

HIJ

ASS

dete

ctio

nsw

ithop

tical

coun

terp

arts

with

inth

egr

idde

dbe

amsi

ze.

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

)(a

rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

HIJ

ASS

J104

8+46

10:4

8:43

.33

46:4

3:10

.02.

774

1±

6ID

UG

C05

917

10:4

8:53

.73

46:4

3:14

.674

11.

80

HIJ

ASS

J105

4+49

10:5

4:57

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49:4

2:53

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913

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15ID

UG

C06

029

10:5

5:02

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49:4

3:33

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631.

016

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502.

69+4

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10:5

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49:4

3:40

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571.

110

HIJ

ASS

J110

2+52

11:0

2:48

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52:0

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094

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7ID

UG

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113

11:0

2:47

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6:48

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10.

12

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ASS

J110

8+53

11:0

8:08

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53:3

6:41

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112

26±

6ID

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182

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912

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801.

86+5

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2.7

11:0

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53:3

7:02

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761.

150

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819.

94+5

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11:0

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871.

713

9H

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109+

5011

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32.5

350

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050

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36.3

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110+

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511

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58.3

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41.6

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25.9

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111

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311

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ASS

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7ID

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399

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55.5

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126+

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41.0

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GC

3769

A11

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51.3

647

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52.8

734

1.5

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138+

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00.2

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55.5

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311

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335

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13.0

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138+

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44.7

533

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43.6

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011

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20.8

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c11

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139+

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811

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545

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31.8

841

0.2

7

at Swinburne U




ownloaded from



Tabl

e2

–co

ntin

ued

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

)(a

rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

––

––

––

J114

035.

57+4

6072

7.5

11:4

0:35

.58

46:0

7:27

.684

312

.35

HIJ

ASS

J114

1+46

11:4

1:11

.61

46:2

4:10

.91.

674

3±

5ID

CG

CG

242−

075

11:4

1:21

.97

46:2

3:35

.574

31.

90

HIJ

ASS

J114

1+36

11:4

1:20

.37

36:3

2:41

.51.

614

67±

7ID

NG

C38

1311

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18.6

636

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48.5

1465

0.4

2H

IJA

SSJ1

141+

3211

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26.2

332

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29.4

2.0

1820

±8

IDM

rk07

4611

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29.8

632

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59.5

1801

2.6

19–

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UG

1138

+327

11:4

1:07

.49

32:2

5:37

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968.

224

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S28

11:4

1:36

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32:1

6:51

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692.

851

HIJ

ASS

J114

2+51

11:4

2:22

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51:3

3:35

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398

6±

10ID

UG

C06

667

11:4

2:26

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51:3

5:52

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32.

413

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J114

226.

26+5

1355

2.6

11:4

2:26

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51:3

5:52

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342.

448

HIJ

ASS

J114

3+31

11:4

3:18

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617

93±

5ID

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880.

55

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C06

684N

OT

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111

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32.7

231

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1813

3.0

20H

IJA

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144+

4811

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23.7

148

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40.4

1.9

899

±5

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0671

311

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24.9

748

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06.8

899

0.5

0H

IJA

SSJ1

145+

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06.2

650

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02.4

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1630

±15

IDJ1

1450

6.26

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802.

411

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06.2

650

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02.4

1664

0.0

34H

IJA

SSJ1

146+

5011

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00.0

450

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16.2

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HIJ

ASS

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6+47

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7711

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149+

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211

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149+

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39.6

648

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113.

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ASS

J115

0+38

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38:5

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ASS

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1+38

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3011

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46.0

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SSJ1

151+

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48.0

548

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1.5

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GC

3928

11:5

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48:4

0:59

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55

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056.

11+4

8315

3.8

11:5

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48:3

1:53

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812

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HIJ

ASS

J115

2+52

11:5

2:05

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52:0

6:00

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210

15±

4ID

UG

C06

840

11:5

2:07

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52:0

6:28

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460.

531

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NG

C39

17A

11:5

1:13

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52:0

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710

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1511

3.45

+520

003.

111

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13.4

552

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03.1

908

10.0

107

HIJ

ASS

J115

2+44

11:5

2:47

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44:0

6:56

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480

8±

2ID

NG

C39

3811

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49.4

544

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14.6

809

0.5

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1524

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602.

011

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44.4

244

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02.0

842

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34H

IJA

SSJ1

152+

5011

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48.6

050

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18.7

1.7

994

±6

IDU

GC

0684

911

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39.1

650

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16.0

995

2.5

1H

IJA

SSJ1

152+

3711

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53.6

637

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19.9

1.5

934

±6

IDN

GC

3941

11:5

2:55

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36:5

9:10

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81.

26

HIJ

ASS

J115

3+47

11:5

3:37

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47:5

1:14

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879

0±

8ID

NG

C39

4911

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41.7

247

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31.4

800

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1534

0.69

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156.

411

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40.7

047

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56.5

855

0.8

65H

IJA

SSJ1

153+

5211

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44.9

652

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35.9

0.9

1048

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IDN

GC

3953

11:5

3:48

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52:1

9:36

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521.

24

at Swinburne U




ownloaded from



Tabl

e2

–co

ntin

ued

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

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rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

HIJ

ASS

J115

4+30

11:5

4:12

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30:0

7:20

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997

4±

9ID

eJ1

1540

4.42

+300

634.

611

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04.4

230

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34.6

981

1.8

7H

IJA

SSJ1

156+

5011

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24.9

650

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04.9

0.6

915

±3

IDU

GC

0691

711

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26.5

250

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43.2

911

0.7

4H

IJA

SSJ1

156+

4811

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36.5

848

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30.9

0.9

945

±7

IDN

GC

3985

11:5

6:42

.11

48:2

0:02

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81.

13

HIJ

ASS

J115

7+50

11:5

7:02

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50:4

8:51

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189

4±

4ID

UG

C06

922

11:5

6:52

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50:4

9:01

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71.

717

HIJ

ASS

J115

7+49

11:5

7:16

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49:1

6:24

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777

6±

3ID

UG

C06

930

11:5

7:17

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49:1

6:59

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70.

61

HIJ

ASS

J115

7+53

11:5

7:32

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53:2

0:51

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010

50±

4ID

ME

SSIE

R10

911

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35.9

853

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28.3

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GC

0692

311

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49.4

353

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37.3

1066

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GC

0694

011

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47.5

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811

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453

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43.8

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3093

7.5

11:5

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53:0

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012

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HIJ

ASS

J115

8+38

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38:0

4:18

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090

1±

4ID

UG

C06

955

11:5

8:29

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38:0

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44

HIJ

ASS

J115

8+50

11:5

8:31

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50:5

1:54

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794

1±

5ID

UG

C06

956

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2611

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25.1

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501.

211

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25.6

050

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01.2

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102

HIJ

ASS

J115

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43:5

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282

9±

5ID

NG

C40

1311

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31.3

843

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47.7

831

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158+

4711

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37.0

847

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47.4

1.4

904

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IDN

GC

4010

11:5

8:37

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47:1

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20.

92

HIJ

ASS

J115

8+42

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8:44

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42:4

3:06

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671

3±

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5011

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52.2

042

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20.9

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294

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31+4

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42:4

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212

7H

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158+

4511

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49.8

945

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37.1

0.7

1148

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IDU

GC

A25

911

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53.2

745

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04.1

1154

1.6

6H

IJA

SSJ1

158+

3011

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52.2

530

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15.5

2.3

769

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IDN

GC

4020

11:5

8:56

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30:2

4:42

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01.

19

HIJ

ASS

J115

9+52

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9:03

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52:4

1:45

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210

84±

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983

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382

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3±

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007

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770

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NG

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412

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770

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204+

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00.3

652

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51.9

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4068

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45

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4+31

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31:5

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575

9±

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NG

C40

6212

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03.8

331

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44.9

758

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1H

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SSJ1

205+

5012

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31.7

250

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56.1

0.6

753

±3

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GC

4088

12:0

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50:3

2:20

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71.

54

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NG

C40

8512

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22.7

150

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10.6

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2054

3.59

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318.

912

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43.5

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18.9

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79+5

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52.

310

8–

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2053

1.00

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143.

912

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31.0

050

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43.9

914

0.8

161

HIJ

ASS

J120

5+47

12:0

5:59

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47:2

7:42

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856

7±

6ID

NG

C40

9612

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01.1

347

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42.4

566

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2055

6.52

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625.

912

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56.5

247

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25.9

381

1.3

186

HIJ

ASS

J120

6+49

12:0

6:07

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49:3

4:30

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110

84±

9ID

NG

C41

0012

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08.4

549

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57.6

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8.59

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912

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08.5

949

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00.0

1097

0.5

13H

IJA

SSJ1

206+

4312

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25.2

743

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15.8

2.1

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4111

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43:0

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76.

92

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UG

C07

089

12:0

5:57

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43:0

8:36

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335

at Swinburne U




ownloaded from



Tabl

e2

–co

ntin

ued

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

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(J20

00.0

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rcm

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(km

s−1)

Cla

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ED

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b(J

2000

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(J20

00.0

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ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

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J120

559.

63+4

2540

9.1

12:0

5:59

.00

42:5

4:10

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710

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12:0

6:10

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42:5

7:20

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96.

526

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NG

C41

1712

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46.1

143

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34.9

934

15.4

129

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NG

C41

1812

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52.8

743

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39.8

643

16.4

162

HIJ

ASS

J120

7+39

12:0

7:41

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39:5

2:05

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386

5±

8ID

UG

CA

271

12:0

7:23

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39:4

8:46

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74.

812

HIJ

ASS

J120

8+36

12:0

8:39

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36:4

8:23

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710

70±

3ID

UG

C07

125

12:0

8:42

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36:4

8:09

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710.

71

HIJ

ASS

J120

9+30

12:0

9:11

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30:5

5:26

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425

2±

9ID

UG

C07

131

12:0

9:11

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30:5

4:24

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31.

01

HIJ

ASS

J120

9+29

12:0

9:15

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29:5

5:31

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560

6±

3ID

NG

C41

3612

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17.6

929

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39.4

609

0.4

3H

IJA

SSJ1

209+

5312

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25.7

353

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55.8

1.6

1163

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IDN

GC

4142

12:0

9:30

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53:0

6:17

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570.

86

HIJ

ASS

J120

9+43

A12

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29.3

443

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02.5

1.5

893

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IDN

GC

4138

12:0

9:29

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43:4

1:07

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81.

15

HIJ

ASS

J120

9+43

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39.7

143

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58.1

2.0

1057

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IDU

GC

0714

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49.1

543

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04.9

1065

2.0

8H

IJA

SSJ1

210+

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00.7

846

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22.5

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47

HIJ

ASS

J121

0+39

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03.9

739

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17.4

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C41

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12:1

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02.6

750

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17.1

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8212

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22.5

750

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10.3

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516

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09.1

636

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20.6

229

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07.5

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38

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J121

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HIJ

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246

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.90

47:0

5:30

.410

270.

34

HIJ

ASS

J121

6+52

12:1

6:05

.74

52:1

8:40

.40.

716

8±

3ID

UG

C07

298

12:1

6:30

.10

52:1

3:39

.017

36.

35

––

––

––

CG

CG

269−

049

12:1

5:46

.62

52:2

3:13

.915

95.

49

at Swinburne U




ownloaded from



Tabl

e2

–co

ntin

ued

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

)(a

rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

HIJ

ASS

J121

6+46

12:1

6:42

.36

46:0

3:53

.22.

070

7±

5ID

UG

C07

301

12:1

6:42

.08

46:0

4:43

.669

00.

817

HIJ

ASS

J121

6+28

12:1

6:44

.02

28:4

3:43

.41.

112

10±

4ID

UG

C07

300

12:1

6:43

.31

28:4

3:52

.112

100.

20

––

––

––

[YW

P201

0]J1

84.1

76+2

8.73

012

:16:

42.2

428

:43:

48.0

1218

0.4

8H

IJA

SSJ1

217+

4512

:17:

26.8

045

:36:

29.5

0.7

511

±3

IDN

GC

4242

12:1

7:30

.18

45:3

7:09

.550

60.

95

HIJ

ASS

J121

7+37

12:1

7:28

.41

37:4

8:08

.90.

224

3±

2ID

NG

C42

4412

:17:

29.6

637

:48:

25.6

244

0.4

1–

––

––

–H

S12

14+3

801

12:1

7:09

.68

37:4

4:53

.633

04.

987

HIJ

ASS

J121

7+22

12:1

7:34

.22

22:3

2:42

.31.

540

0±

6ID

UG

C07

321

12:1

7:34

.01

22:3

2:24

.540

80.

38

HIJ

ASS

J121

8+46

12:1

8:11

.04

46:5

5:01

.21.

833

3±

5ID

J121

811.

04+4

6550

1.2

12:1

8:11

.07

46:5

5:00

.747

20.

013

9H

IJA

SSJ1

218+

4712

:18:

53.6

847

:17:

19.6

0.3

446

±2

IDM

ESS

IER

106

12:1

8:57

.50

47:1

8:14

.344

81.

12

––

––

––

NG

C42

4812

:17:

49.8

547

:24:

33.1

484

13.0

38–

––

––

–U

GC

0735

612

:19:

09.3

947

:05:

27.5

272

12.2

174

––

––

––

J121

855.

34+4

7164

7.9

12:1

8:55

.34

47:1

6:47

.942

90.

617

––

––

––

J121

901.

36+4

7152

5.0

12:1

9:01

.36

47:1

5:25

.033

02.

311

6H

IJA

SSJ1

219+

4612

:19:

52.7

846

:35:

27.3

1.2

392

±3

PUO

––

––

––

HIJ

ASS

J122

0+45

12:2

0:16

.24

45:5

4:30

.22.

572

8±

9ID

UG

C07

391

12:2

0:16

.24

45:5

4:30

.261

20.

011

6H

IJA

SSJ1

220+

2912

:20:

19.2

729

:15:

18.5

2.6

611

±11

IDN

GC

4278

12:2

0:06

.82

29:1

6:50

.764

93.

138

––

––

––

J122

017.

40+2

9060

9.1

12:2

0:17

.40

29:0

6:09

.171

09.

299

––

––

––

NG

C42

8612

:20:

42.0

929

:20:

45.2

644

7.4

33H

IJA

SSJ1

220+

4712

:20:

34.8

547

:49:

04.8

2.4

729

±9

IDU

GC

0740

112

:20:

48.4

247

:49:

33.4

762

2.3

33H

IJA

SSJ1

220+

4612

:20:

36.6

746

:17:

14.0

0.5

518

±5

IDN

GC

4288

12:2

0:38

.11

46:1

7:30

.052

00.

42

HIJ

ASS

J122

0+38

12:2

0:56

.87

38:2

5:06

.91.

257

4±

4ID

KU

G12

18+3

8712

:20:

54.8

838

:25:

48.7

606

0.8

32H

IJA

SSJ1

221+

4512

:21:

14.2

945

:48:

02.6

0.3

460

±2

IDU

GC

0740

812

:21:

15.0

145

:48:

40.8

462

0.6

2–

––

––

–U

GC

0739

112

:20:

16.2

445

:54:

30.2

612

12.0

152

HIJ

ASS

J122

1+35

12:2

1:53

.81

35:0

4:20

.31.

773

0±

5ID

UG

C07

427

12:2

1:54

.86

35:0

3:00

.372

41.

46

HIJ

ASS

J122

2+32

12:2

2:04

.36

32:0

5:16

.31.

811

44±

7ID

UG

C07

428

12:2

2:02

.61

32:0

5:45

.411

370.

67

HIJ

ASS

J122

2+39

12:2

2:07

.09

39:4

5:43

.42.

010

73±

5ID

J122

206.

12+3

9445

2.4

12:2

2:06

.12

39:4

4:52

.411

020.

929

HIJ

ASS

J122

4+31

12:2

4:11

.84

31:3

0:47

.13.

412

52±

8ID

NG

C43

5912

:24:

11.1

731

:31:

19.0

1253

0.6

1H

IJA

SSJ1

224+

3912

:24:

33.1

839

:21:

47.2

2.7

1032

±13

IDN

GC

4369

12:2

4:36

.20

39:2

2:58

.810

451.

313

HIJ

ASS

J122

5+26

12:2

5:22

.45

26:4

3:48

.72.

831

8±

12ID

IC33

0812

:25:

18.2

126

:42:

54.4

316

1.3

2–

––

––

–J1

2252

0.71

+264

210.

212

:25:

20.7

126

:42:

10.2

342

1.7

24H

IJA

SSJ1

225+

2812

:25:

28.6

128

:29:

13.6

1.8

475

±8

IDO

321

0767

130d

12:2

5:29

.15

28:2

8:56

.848

30.

38

HIJ

ASS

J122

5+45

12:2

5:30

.67

45:3

9:36

.82.

371

4±

7ID

NG

C43

8912

:25:

35.1

045

:41:

04.8

718

1.7

4H

IJA

SSJ1

225+

2712

:25:

50.4

727

:33:

53.0

0.7

751

±3

IDN

GC

4393

12:2

5:51

.23

27:3

3:41

.675

50.

34

HIJ

ASS

J122

5+33

12:2

5:51

.37

33:3

3:00

.60.

231

7±

2ID

NG

C43

9512

:25:

48.8

633

:32:

48.9

319

0.6

2H

IJA

SSJ1

226+

3112

:26:

23.2

331

:13:

20.1

1.1

711

±7

IDN

GC

4414

12:2

6:27

.10

31:1

3:24

.771

60.

85

HIJ

ASS

J122

6+27

12:2

6:23

.34

27:4

4:43

.93.

337

3±

10ID

fIC

3341

12:2

6:23

.19

27:4

4:43

.937

20.

01

HIJ

ASS

J122

7+37

12:2

7:07

.60

37:0

8:13

.00.

321

5±

2ID

UG

C07

559

12:2

7:05

.15

37:0

8:33

.421

80.

63

HIJ

ASS

J122

7+43

12:2

7:37

.06

43:2

9:48

.10.

319

5±

2ID

UG

C07

577

12:2

7:40

.90

43:2

9:44

.019

50.

70

HIJ

ASS

J122

8+22

A12

:28:

02.8

322

:35:

15.8

1.7

592

±4

IDU

GC

0758

412

:28:

02.8

322

:35:

15.8

603

0.0

11H

IJA

SSJ1

228+

4412

:28:

06.3

344

:05:

56.9

0.1

205

±3

IDN

GC

4449

12:2

8:11

.10

44:0

5:37

.120

70.

92

at Swinburne U




ownloaded from



Tabl

e2

–co

ntin

ued

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

)(a

rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

HIJ

ASS

J122

8+37

12:2

8:21

.72

37:1

3:53

.70.

526

0±

4ID

UG

C07

599

12:2

8:28

.56

37:1

4:01

.127

81.

418

HIJ

ASS

J122

8+35

12:2

8:36

.15

35:4

3:36

.41.

231

1±

5ID

UG

C07

605

12:2

8:38

.74

35:4

3:02

.931

00.

81

HIJ

ASS

J122

8+43

12:2

8:41

.00

43:1

3:13

.90.

353

6±

2ID

UG

C07

608

12:2

8:44

.20

43:1

3:26

.953

80.

62

HIJ

ASS

J122

8+22

B12

:28:

41.9

222

:49:

00.3

0.6

642

±2

IDN

GC

4455

12:2

8:44

.11

22:4

9:13

.663

70.

65

HIJ

ASS

J122

8+42

12:2

8:52

.22

42:1

0:40

.52.

041

7±

9ID

MC

G+0

7-26

-011

12:2

8:52

.23

42:1

0:40

.540

80.

09

HIJ

ASS

J123

0+42

12:3

0:23

.57

42:5

4:05

.71.

538

1±

7ID

MC

G+0

7-26

-012

12:3

0:23

.57

42:5

4:05

.743

60.

055

––

––

––

J123

023.

60+4

2540

5.7

12:3

0:23

.60

42:5

4:05

.752

20.

014

1H

IJA

SSJ1

230+

4112

:30:

32.6

341

:38:

33.7

0.2

570

±4

IDN

GC

4490

12:3

0:36

.24

41:3

8:38

.056

50.

75

––

––

––

NG

C44

8512

:30:

31.1

341

:42:

04.2

493

3.5

77H

IJA

SSJ1

231+

2912

:31:

56.4

829

:42:

25.7

1.6

644

±4

IDU

GC

0767

312

:31:

58.5

729

:42:

34.6

642

0.5

2H

IJA

SSJ1

232+

3912

:32:

04.8

439

:48:

18.7

0.9

680

±4

IDU

GC

0767

812

:32:

00.1

739

:49:

57.6

666

1.9

14H

IJA

SSJ1

232+

4212

:32:

26.6

942

:41:

41.1

1.0

538

±4

IDU

GC

0769

012

:32:

26.8

942

:42:

14.8

537

0.6

1H

IJA

SSJ1

232+

3712

:32:

46.4

137

:37:

45.9

1.4

503

±6

IDU

GC

0769

912

:32:

48.0

237

:37:

18.4

496

0.6

7H

IJA

SSJ1

232+

3112

:32:

53.4

431

:32:

48.6

0.5

331

±2

IDU

GC

0769

812

:32:

54.3

931

:32:

28.0

331

0.4

0H

IJA

SSJ1

233+

3212

:33:

04.7

132

:06:

54.2

2.1

923

±9

IDN

GC

4509

12:3

3:06

.79

32:0

5:29

.793

71.

514

––

––

––

J123

306.

44+3

2052

7.4

12:3

3:06

.44

32:0

5:27

.591

21.

511

HIJ

ASS

J123

3+33

12:3

3:15

.73

33:2

0:19

.42.

383

0±

12ID

KU

G12

30+3

3612

:33:

24.8

933

:21:

04.5

838

2.1

8H

IJA

SSJ1

233+

24g

12:3

3:39

.50

23:5

9:07

.83.

313

16±

16ID

fO

378

0206

985d

12:3

3:41

.75

23:5

9:13

.613

250.

59

HIJ

ASS

J123

3+39

12:3

3:48

.83

39:3

8:43

.41.

265

8±

4ID

MC

G+0

7-26

-024

12:3

3:52

.74

39:3

7:33

.464

61.

412

HIJ

ASS

J123

3+30

12:3

3:55

.58

30:1

7:56

.42.

311

73±

11ID

NG

C45

2512

:33:

51.1

430

:16:

38.9

1172

1.6

1H

IJA

SSJ1

234+

3912

:34:

03.4

739

:00:

39.9

1.4

679

±4

IDU

GC

0771

912

:34:

00.5

439

:01:

09.0

678

0.7

1H

IJA

SSJ1

234+

3512

:34:

04.0

335

:31:

37.7

0.4

802

±2

IDN

GC

4534

12:3

4:05

.42

35:3

1:06

.080

20.

60

HIJ

ASS

J123

5+41

12:3

5:13

.31

41:0

3:07

.72.

060

8±

6ID

UG

C07

751

12:3

5:11

.77

41:0

3:39

.560

50.

63

HIJ

ASS

J123

5+27

12:3

5:57

.46

27:5

7:32

.30.

281

3±

2ID

NG

C45

5912

:35:

57.6

527

:57:

36.0

807

0.1

6–

––

––

–J1

2355

1.86

+275

557.

012

:35:

51.8

627

:55:

57.0

855

2.0

42H

IJA

SSJ1

236+

2512

:36:

16.7

725

:59:

43.3

0.3

1226

±3

IDN

GC

4565

12:3

6:20

.78

25:5

9:15

.612

301.

04

––

––

––

NG

C45

6212

:35:

34.8

025

:51:

00.0

1353

12.8

127

––

––

––

IC35

7112

:36:

20.1

026

:05:

03.2

1260

5.4

34H

IJA

SSJ1

236+

4012

:36:

19.6

540

:00:

01.1

1.5

522

±5

IDU

GC

0777

412

:36:

22.7

240

:00:

18.7

526

0.7

4H

IJA

SSJ1

238+

3212

:38:

37.2

832

:45:

53.4

0.4

309

±2

IDU

GC

A29

212

:38:

40.0

632

:46:

00.5

308

0.6

1H

IJA

SSJ1

239+

4412

:39:

44.5

244

:49:

11.1

1.3

554

±4

IDU

GC

0782

712

:39:

38.9

344

:49:

14.4

554

1.0

0H

IJA

SSJ1

240+

3212

:40:

10.0

032

:39:

30.0

1.2

759

±6

IDJ1

2401

0.08

+323

930.

412

:40:

10.0

432

:39:

31.6

776

0.0

17H

IJA

SSJ1

241+

4112

:41:

38.2

241

:11:

02.9

0.4

556

±3

IDN

GC

4618

12:4

1:32

.85

41:0

9:02

.854

42.

212

––

––

––

NG

C46

2512

:41:

52.7

241

:16:

26.3

598

6.0

42H

IJA

SSJ1

242+

3212

:42:

06.9

432

:31:

54.0

0.1

610

±2

IDN

GC

4631

12:4

2:08

.01

32:3

2:29

.460

60.

64

––

––

––

J124

146.

99+3

2512

4.8

12:4

1:47

.13

32:5

1:24

.969

620

.086

––

––

––

NG

C46

2712

:41:

59.6

832

:34:

24.8

542

2.9

68H

IJA

SSJ1

242+

3812

:42:

15.5

538

:30:

38.5

0.7

354

±3

IDIC

3687

12:4

2:15

.10

38:3

0:12

.035

40.

50

HIJ

ASS

J124

3+24

12:4

3:05

.87

24:2

7:03

.92.

818

23±

6ID

fK

UG

1240

+247

12:4

3:05

.87

24:2

7:03

.918

250.

02

HIJ

ASS

J124

3+32

12:4

3:51

.42

32:1

0:18

.40.

164

2±

3ID

NG

C46

56N

ED

0112

:43:

57.6

732

:10:

12.9

664

1.3

22

at Swinburne U




ownloaded from


A blind H I survey in the Ursa Major region 13Ta

ble

2–

cont

inue

d

RA

Dec

.σ

pos

v sys

±σ

vR

AD

ec.

Vel

ocity

Posi

tions

and

velo

city

offs

ets

HIJ

ASS

nam

e(J

2000

.0)

(J20

00.0

)(a

rcm

in)

(km

s−1)

Cla

ssN

ED

IDa,

b(J

2000

.0)

(J20

00.0

)(k

ms−1

)(a

rcm

in)

(km

s−1)

(A1)

(A2)

(A3)

(A4)

(A5)

(A6)

(A7)

(A8)

(A9)

(A10

)(A

11)

(A12

)

––

––

––

J124

348.

72+3

2081

3.8

12:4

3:48

.72

32:0

8:13

.870

52.

263

––

––

––

J124

4059

9+32

1234

0c12

:44:

05.9

832

:12:

32.3

617

3.8

25H

IJA

SSJ1

244+

3412

:44:

25.6

334

:23:

24.7

0.7

601

±2

IDU

GC

0791

612

:44:

25.1

434

:23:

11.5

607

0.2

6H

IJA

SSJ1

244+

2812

:44:

36.0

928

:28:

46.4

1.9

936

±6

IDU

GC

A29

412

:44:

38.1

528

:28:

21.0

947

0.6

11H

IJA

SSJ1

245+

2712

:45:

16.6

027

:07:

02.9

1.9

1077

±10

IDN

GC

4670

12:4

5:17

.07

27:0

7:31

.510

690.

58

––

––

––

J124

516.

87+2

7073

0.7

12:4

5:16

.87

27:0

7:30

.810

450.

532

HIJ

ASS

J124

6+36

12:4

6:58

.34

36:2

8:33

.10.

733

2±

3ID

UG

C07

949

12:4

6:59

.80

36:2

8:35

.033

10.

31

HIJ

ASS

J125

0+25

12:5

0:23

.64

25:3

0:27

.10.

212

05±

3ID

NG

C47

2512

:50:

26.5

825

:30:

02.9

1206

0.8

1H

IJA

SSJ1

250+

4112

:50:

54.6

541

:06:

50.3

0.8

304

±4

IDM

ESS

IER

094

12:5

0:53

.06

41:0

7:13

.730

80.

54

HIJ

ASS

J125

1+26

12:5

1:44

.44

26:0

6:37

.81.

512

41±

7ID

KU

G12

49+2

6312

:51:

44.4

526

:06:

37.8

1225

0.0

16H

IJA

SSJ1

251+

2512

:51:

47.9

125

:48:

27.3

0.3

1201

±5

IDN

GC

4747

12:5

1:45

.95

25:4

6:37

.511

901.

911

HIJ

ASS

J125

4+27

12:5

4:03

.66

27:0

9:27

.10.

337

3±

2ID

NG

C47

89A

12:5

4:05

.25

27:0

8:58

.737

40.

61

aT

hem

ostl

ikel

yco

unte

rpar

tof

aH

IJA

SSso

urce

isgi

ven

inth

efir

stro

w.P

oten

tially

conf

used

HIJ

ASS

sour

ces,

with

mul

tiple

gala

xies

with

inth

egr

idde

dbe

amor

the

HI

inte

nsity

cont

ours

(for

larg

eso

urce

s)an

dw

ithin

the

velo

city

rang

eof

the

HIde

tect

ion,

are

liste

din

the

subs

eque

ntro

ws.

bU

nles

sst

ated

diff

eren

tly,i

dent

ifica

tions

star

ting

with

‘J’

are

SDSS

gala

xies

and

thei

rfu

llna

mes

are

ofth

efo

rm:S

DSS

X,w

here

Xis

the

stat

edID

.c 2M

ASX

obje

cts

with

full

iden

tifica

tions

ofth

efo

rm:2

MA

SXY

,whe

reY

isth

est

ated

ID.

dM

APS

-NG

Pob

ject

with

full

iden

tifica

tion

ofth

efo

rm:M

APS

-NG

PZ

,whe

reZ

isth

est

ated

ID.

e Red

shif

tinf

orm

atio

nav

aila

ble

inSD

SSD

R8

(Aih

ara

etal

.201

1)–

notl

iste

din

NE

D.

f Red

shif

tinf

orm

atio

nav

aila

ble

inA

LFA

LFA

(Hay

nes

etal

.201

1)–

notl

iste

din

NE

D.

gH

IJA

SSna

me

cons

iste

ntw

ithL

ang

etal

.(20

03).

measurable (usually weak H I sources or double detections for whichwe retain the optical counterpart position). The projected positionof the Ursa Major cluster as defined by (Tully et al. 1996) is overlaidwith a large circle.

3.3 H I parameter uncertainties

In Table 2 and 3 we give several uncertainties of measured H I

parameters which are calculated as follows.The position uncertainty is derived from the gridded beam size

(FWHM) and the H I signal-to-noise ratio (Koribalski et al. 2004):

σpos = FWHM

Sp/rms.

This individual position uncertainty is considered when determiningthe most likely optical counterpart (see Table 2).

The peak flux uncertainty strongly depends on the rms noise forweak sources and to a lesser degree on the peak flux (see Barneset al. 2001). The formula we use is analogous to the one in HIPASS(Koribalski et al. 2004), which is as follows:

σ 2peak = rms2 + (0.05Sp)2.

The uncertainty in integrated flux is calculated as discussed in Ko-ribalski et al. (2004) whereby

σint = 4 ×(

Sp

rms

)−1

× (Sp × S int × R)0.5,

with R = 18.1 km s−1, which is the velocity resolution of the HIJASSdata.

The systemic velocity uncertainty is

σv = 3 ×(

Sp

σ peak

)−1

× [R × 0.5(w20 − w50)]0.5,

as discussed in Koribalski et al. (2004).The uncertainties in the 50 per cent and 20 per cent velocity

widths are

σ50 = 2 × σv,

σ20 = 3 × σv,

as discussed in Fouque et al. (1990).

3.4 Candidate galaxy/H I cloud

The presented catalogue of 166 H I sources in the Ursa Majorregion contains 162 H I detections, which are clearly associatedwith previously catalogued galaxies as listed in the NED (withcross-identifications) or the Sloan Digital Sky Survey (SDSS DR8– redshift confidence level zconf > 0.95). Another three HIJASSdetections – namely HIJASS J1226+27, HIJASS J1243+24 andHIJASS J1233+24 – can be matched up with H I sources listedin the ALFALFA 40 per cent catalogue (Haynes et al. 2011) andhave been assigned to IC 3341, KUG 1240+247 and MAPS-NGPO 378 0206985, respectively. Note that HIJASS J1233+24 wasfirst catalogued in Lang et al. (2003) using the same HIJASS dataset and is therefore listed in NED (without cross-identifications).Therefore, only one H I detection – HIJASS J1219+46 – does nothave a previously catalogued optical counterpart with known ve-locity listed in NED, SDSS or ALFALFA (HIJASS J1219+46 liesoutside the ALFALFA declination range).

To identify a potential optical counterpart of the candidategalaxy/H I cloud we investigate SDSS and DSS images. We compare

at Swinburne U




ownloaded from



Tabl

e3.

The

HIpr

oper

ties

ofal

lHIJ

ASS

dete

ctio

ns.

S pS p

(cor

r)σ

peak

S int

S int

(cor

r)σ

int

w50

±σ

50w

20±

σ20

rms

Dis

tanc

eH

IJA

SSna

me

(Jy)

(Jy)

(Jy)

(Jy

kms−

1)

(Jy

kms−

1)

(Jy

kms−

1)

(km

s−1)

(km

s−1)

(Jy)

(Mpc

)lo

gM

HI

Flag

sa

(B1)

(B2)

(B3)

(B4)

(B5)

(B6)

(B7)

(B8)

(B9)

(B10

)(B

11)

(B12

)(B

13)

HIJ

ASS

J104

8+46

0.05

9–

0.01

24.

22–

1.73

98±

1211

0±

180.

012

11.1

8.09

HIJ

ASS

J105

4+49

0.10

10.

091

0.02

110

.35

11.5

43.

8312

4±

3017

3±

450.

020

20.0

9.04

ecH

IJA

SSJ1

102+

520.

106

–0.

017

4.39

–1.

7546

±14

68±

210.

016

14.5

8.34

HIJ

ASS

J110

8+53

0.10

90.

098

0.01

78.

759.

762.

7294

±12

109

±18

0.01

618

.68.

90ec

3H

IJA

SSJ1

109+

500.

074

–0.

010

6.91

–1.

4812

5±

1415

5±

210.

009

13.9

8.50

nH

IJA

SSJ1

110+

460.

069

–0.

011

6.54

–1.

6612

0±

1213

5±

180.

010

20.7

8.82

HIJ

ASS

J111

3+53

0.26

9–

0.01

710

.76

–1.

0844

±4

61±

60.

010

14.4

8.72

cH

IJA

SSJ1

120+

530.

560

–0.

031

49.6

–2.

0810

1±

412

5±

60.

013

17.1

9.53

cdH

IJA

SSJ1

123+

500.

069

–0.

014

8.48

–2.

6417

7±

1419

3±

210.

014

17.1

8.77

HIJ

ASS

J112

3+52

0.21

8–

0.01

534

.23

–2.

1319

7±

621

9±

90.

010

18.4

9.44

dH

IJA

SSJ1

126+

530.

333

0.29

80.

027

35.9

540

.34.

3513

0±

614

2±

90.

022

10.4

9.01

eH

IJA

SSJ1

132+

530.

540

0.47

70.

032

151.

0917

0.97

6.77

467

±6

488

±9

0.02

117

.110

.07

ecH

IJA

SSJ1

132+

390.

103

–0.

014

8.11

–1.

9682

±14

115

±21

0.01

322

.58.

98H

IJA

SSJ1

133+

470.

532

0.47

60.

033

94.2

110

5.75

5.83

262

±6

282

±9

0.02

317

.19.

86ec

HIJ

ASS

J113

3+49

0.05

9–

0.00

92.

12–

0.92

40±

1052

±15

0.00

94.

26.

95vi

HIJ

ASS

J113

6+45

0.62

2–

0.03

348

.51

–1.

5083

±4

100

±6

0.01

03.

28.

07vi

HIJ

ASS

J113

6+36

0.17

40.

157

0.01

940

.68

45.4

14.

9226

7±

1028

9±

150.

017

22.5

9.73

ecH

IJA

SSJ1

137+

470.

354

0.31

70.

022

53.3

359

.83.

5121

3±

825

5±

120.

015

17.1

9.61

ecH

IJA

SSJ1

138+

350.

104

0.09

70.

014

10.3

811

.35

2.39

160

±16

197

±24

0.01

323

.29.

16e

HIJ

ASS

J113

8+33

0.07

80.

072

0.01

39.

8110

.82

2.50

199

±12

212

±18

0.01

226

.39.

25ec

HIJ

ASS

J113

8+43

0.04

7–

0.00

65.

26–

1.08

156

±16

206

±24

0.00

617

.18.

56cn

HIJ

ASS

J113

9+46

0.34

6–

0.02

228

.55

–2.

0189

±6

125

±9

0.01

317

.19.

29cd

HIJ

ASS

J114

0+45

0.65

50.

587

0.03

725

.728

.82.

6241

±4

59±

60.

022

17.1

9.30

ecH

IJA

SSJ1

141+

460.

057

–0.

008

4.45

–1.

0510

3±

1012

1±

150.

007

17.1

8.49

dnH

IJA

SSJ1

141+

360.

147

0.13

40.

017

32.2

435

.73

4.45

273

±14

312

±21

0.01

621

.09.

57e

HIJ

ASS

J114

1+32

0.09

30.

085

0.01

49.

6010

.62

2.47

129

±16

158

±24

0.01

325

.89.

22ec

nH

IJA

SSJ1

142+

510.

058

–0.

010

8.75

–2.

0918

4±

2022

5±

300.

010

17.1

8.78

cH

IJA

SSJ1

143+

310.

064

–0.

009

7.62

–1.

4914

8±

1016

5±

150.

008

25.4

9.06

cH

IJA

SSJ1

144+

480.

176

0.15

90.

024

13.0

914

.61

3.75

88±

1010

4±

150.

023

17.1

9.00

eH

IJA

SSJ1

145+

500.

042

–0.

011

2.48

–1.

4471

±30

109

±45

0.01

124

.38.

54fn

HIJ

ASS

J114

6+50

0.06

8–

0.01

35.

18–

1.93

86±

2212

9±

330.

013

17.1

8.55

HIJ

ASS

J114

6+47

0.09

9–

0.01

118

.65

–2.

3433

7±

1036

3±

150.

010

17.1

9.11

cH

IJA

SSJ1

147+

490.

070

–0.

013

2.74

–1.

2875

±14

93±

210.

012

17.1

8.28

bH

IJA

SSJ1

148+

480.

348

–0.

020

82.6

–2.

6226

2±

630

6±

90.

010

17.1

9.76

cdH

IJA

SSJ1

149+

390.

123

0.11

40.

020

12.0

513

.25

3.49

158

±14

175

±21

0.01

912

.58.

69e

HIJ

ASS

J114

9+48

0.13

7–

0.01

45.

39–

1.28

42±

858

±12

0.01

217

.18.

57d

HIJ

ASS

J114

9+51

0.05

2–

0.01

25.

75–

2.15

152

±22

178

±33

0.01

219

.18.

70cd

HIJ

ASS

J115

0+45

0.10

00.

093

0.01

511

.74

12.9

12.

8114

6±

1617

3±

240.

014

17.1

8.95

e

at Swinburne U




ownloaded from



Tabl

e3

–co

ntin

ued

S pS p

(cor

r)σ

peak

S int

S int

(cor

r)σ

int

w50

±σ

50w

20±

σ20

rms

Dis

tanc

eH

IJA

SSna

me

(Jy)

(Jy)

(Jy)

(Jy

kms−

1)

(Jy

kms−

1)

(Jy

kms−

1)

(km

s−1)

(km

s−1)

(Jy)

(Mpc

)lo

gM

HI

Flag

sa

(B1)

(B2)

(B3)

(B4)

(B5)

(B6)

(B7)

(B8)

(B9)

(B10

)(B

11)

(B12

)(B

13)

HIJ

ASS

J115

0+51

0.13

0–

0.01

323

.81

–2.

5327

8±

629

2±

90.

011

17.1

9.21

cdH

IJA

SSJ1

150+

380.

926

–0.

048

38.2

6–

1.31

42±

468

±6

0.01

22.

67.

80vi

HIJ

ASS

J115

1+38

0.23

50.

210

0.01

628

.21

31.6

62.

5115

1±

616

8±

90.

012

13.3

9.12

e3H

IJA

SSJ1

151+

480.

090

–0.

011

6.06

–1.

4063

±14

102

±21

0.01

016

.98.

61ci

HIJ

ASS

J115

2+52

0.11

6–

0.01

214

.28

–2.

0813

8±

815

8±

120.

011

17.1

8.99

cdH

IJA

SSJ1

152+

440.

904

0.80

80.

046

76.0

285

.37

4.02

93±

411

2±

60.

023

17.1

9.77

ecH

IJA

SSJ1

152+

500.

076

–0.

011

5.61

–1.

4688

±12

108

±18

0.01

017

.18.

59H

IJA

SSJ1

152+

370.

078

–0.

010

15.2

9–

2.14

262

±12

286

±18

0.00

912

.28.

73i

HIJ

ASS

J115

3+47

0.20

70.

187

0.02

841

.31

46.0

16.

9425

1±

1628

2±

240.

026

17.1

9.50

ecH

IJA

SSJ1

153+

520.

165

–0.

014

38.2

–2.

8540

3±

842

7±

120.

011

17.1

9.42

dH

IJA

SSJ1

154+

300.

063

–0.

010

3.58

–1.

1551

±18

91±

270.

009

13.6

8.20

nH

IJA

SSJ1

156+

500.

164

–0.

011

22.8

3–

1.61

184

±6

206

±9

0.00

817

.19.

20d5

HIJ

ASS

J115

6+48

0.14

0–

0.01

213

.21

–1.

6592

±14

169

±21

0.01

017

.18.

96H

IJA

SSJ1

157+

500.

107

–0.

010

8.93

–1.

4011

8±

813

9±

120.

009

17.1

8.79

dH

IJA

SSJ1

157+

490.

359

0.32

30.

023

37.5

341

.95

3.30

121

±6

138

±9

0.01

717

.19.

46e

HIJ

ASS

J115

7+53

0.30

60.

271

0.02

580

.95

91.3

96.

5645

7±

848

4±

120.

021

17.1

9.80

ecH

IJA

SSJ1

158+

380.

297

0.26

60.

025

35.3

339

.61

4.36

148

±8

166

±12

0.02

113

.29.

21e

HIJ

ASS

J115

8+50

0.20

7–

0.01

511

.46

–1.

3958

±10

120

±15

0.01

117

.18.

90cd

HIJ

ASS

J115

8+43

0.18

90.

174

0.01

834

.32

37.8

64.

0238

7±

1041

1±

150.

016

17.1

9.42

eH

IJA

SSJ1

158+

470.

161

0.14

60.

018

34.1

938

.03

4.39

253

±10

275

±15

0.01

617

.19.

42e

HIJ

ASS

J115

8+42

0.10

30.

097

0.01

322

.224

.21

3.23

366

±12

389

±18

0.01

217

.19.

22ec

HIJ

ASS

J115

8+45

0.14

2–

0.01

16.

43–

0.92

46±

662

±9

0.00

817

.18.

65H

IJA

SSJ1

158+

300.

099

0.09

10.

017

12.3

513

.63

3.33

152

±16

172

±24

0.01

610

.88.

57e

HIJ

ASS

J115

9+52

0.24

20.

218

0.02

330

.03

33.5

24.

2217

5±

819

1±

120.

020

17.1

9.36

ecH

IJA

SSJ1

201+

330.

070

–0.

011

2.86

–1.

0951

±16

82±

240.

010

11.2

7.93

HIJ

ASS

J120

3+44

0.18

50.

168

0.02

434

.28

38.0

85.

6423

7±

1627

8±

240.

022

17.1

9.42

ecH

IJA

SSJ1

204+

520.

623

–0.

033

32.3

1–

1.23

55±

481

±6

0.01

04.

48.

16vi

HIJ

ASS

J120

4+31

0.11

00.

103

0.02

120

.58

22.5

5.03

295

±20

327

±30

0.02

010

.88.

79e

HIJ

ASS

J120

5+50

0.52

90.

463

0.03

213

7.08

156.

126.

8733

0±

635

4±

90.

022

17.1

10.0

3ec

HIJ

ASS

J120

5+47

0.42

00.

378

0.03

072

.080

.54

5.71

250

±12

327

±18

0.02

39.

19.

19ec

HIJ

ASS

J120

6+49

0.21

90.

199

0.02

037

.93

42.1

74.

2128

2±

1837

6±

270.

017

17.1

9.46

ecH

IJA

SSJ1

206+

430.

284

0.23

10.

039

47.5

959

.63

10.1

223

0±

2428

7±

360.

037

15.0

9.50

eci

HIJ

ASS

J120

7+39

0.09

20.

080

0.02

02.

492.

862.

0448

±16

62±

240.

020

12.8

8.05

eH

IJA

SSJ1

208+

360.

442

0.39

10.

029

50.1

656

.75

4.31

149

±6

166

±9

0.02

115

.69.

51e

HIJ

ASS

J120

9+30

0.06

5–

0.01

26.

58–

2.05

115

±18

142

±27

0.01

23.

57.

28v

HIJ

ASS

J120

9+29

0.59

60.

529

0.03

451

.36

57.9

53.

9288

±6

110

±9

0.02

28.

58.

99e

HIJ

ASS

J120

9+53

0.08

1–

0.01

111

.46

–2.

0217

3±

1018

8±

150.

010

17.1

8.90

HIJ

ASS

J120

9+43

A0.

093

–0.

012

20.0

8–

2.75

277

±18

336

±27

0.01

113

.88.

95i

HIJ

ASS

J120

9+43

B0.

065

–0.

011

3.79

–1.

3067

±12

82±

180.

010

17.1

8.42

nH

IJA

SSJ1

210+

460.

429

0.38

40.

031

57.2

964

.28

5.28

160

±6

181

±9

0.02

46.

98.

85ev

i

at Swinburne U




ownloaded from



Tabl

e3

–co

ntin

ued

S pS p

(cor

r)σ

peak

S int

S int

(cor

r)σ

int

w50

±σ

50w

20±

σ20

rms

Dis

tanc

eH

IJA

SSna

me

(Jy)

(Jy)

(Jy)

(Jy

kms−

1)

(Jy

kms−

1)

(Jy

kms−

1)

(km

s−1)

(km

s−1)

(Jy)

(Mpc

)lo

gM

HI

Flag

sa

(B1)

(B2)

(B3)

(B4)

(B5)

(B6)

(B7)

(B8)

(B9)

(B10

)(B

11)

(B12

)(B

13)

HIJ

ASS

J121

0+39

A0.

361

–0.

021

57.0

4–

2.35

218

±4

235

±6

0.01

115

.09.

48cd

HIJ

ASS

J121

0+39

B0.

559

–0.

030

51.9

7–

1.97

121

±4

141

±6

0.01

214

.79.

42cd

HIJ

ASS

J121

1+50

0.48

90.

436

0.03

312

2.01

137.

237.

5539

8±

642

2±

90.

025

17.1

9.98

ecH

IJA

SSJ1

212+

360.

226

–0.

014

6.96

–0.

7634

±4

50±

60.

008

3.0

7.16

viH

IJA

SSJ1

212+

290.

391

0.35

10.

031

43.4

848

.65

5.01

159

±8

179

±12

0.02

515

.89.

46e

HIJ

ASS

J121

2+37

0.09

5–

0.01

46.

89–

1.88

79±

1410

6±

210.

013

15.4

8.58

HIJ

ASS

J121

3+52

0.05

6–

0.01

04.

03–

1.44

86±

1410

5±

210.

010

17.1

8.44

HIJ

ASS

J121

3+43

0.37

60.

337

0.03

057

.46

64.3

85.

8823

5±

625

2±

90.

025

17.1

9.65

eH

IJA

SSJ1

213+

240.

080

–0.

009

3.97

–0.

9656

±8

71±

120.

008

13.0

8.20

HIJ

ASS

J121

3+36

0.42

4–

0.02

420

.02

–1.

2951

±6

76±

90.

011

2.8

7.57

dbvi

HIJ

ASS

J121

5+35

0.16

00.

143

0.01

812

.113

.57

2.65

75±

1411

1±

210.

016

13.7

8.78

ecH

IJA

SSJ1

215+

330.

162

0.14

60.

024

30.2

133

.76

5.95

232

±22

291

±33

0.02

315

.19.

26ec

iH

IJA

SSJ1

215+

510.

106

–0.

011

11.1

4–

1.74

114

±10

147

±15

0.01

07.

98.

21H

IJA

SSJ1

215+

430.

078

–0.

008

5.82

–1.

0389

±10

115

±15

0.00

78.

78.

01H

IJA

SSJ1

215+

363.

438

–0.

172

206.

03–

1.45

64±

490

±6

0.01

12.

98.

60cd

bvi

HIJ

ASS

J121

5+48

0.07

1–

0.01

37.

64–

2.29

140

±16

165

±24

0.01

317

.18.

72c

HIJ

ASS

J121

5+47

0.12

3–

0.01

434

.83

–3.

7239

0±

1242

1±

180.

013

17.1

9.38

5H

IJA

SSJ1

216+

520.

293

0.25

00.

019

8.68

10.1

31.

5234

±6

55±

90.

014

4.2

7.62

ecvi

HIJ

ASS

J121

6+46

0.05

3–

0.00

85.

98–

1.45

143

±10

155

±15

0.00

817

.18.

61H

IJA

SSJ1

216+

280.

189

0.17

10.

016

11.7

13.0

12.

0869

±8

94±

120.

014

17.1

8.95

eH

IJA

SSJ1

217+

450.

426

0.38

30.

029

42.2

747

.27

4.16

114

±6

135

±9

0.02

28.

28.

88e

HIJ

ASS

J121

7+37

2.63

92.

263

0.11

737

7.52

437.

736.

6320

1±

422

1±

60.

028

4.3

9.28

ecbv

iH

IJA

SSJ1

217+

220.

246

0.22

30.

028

35.4

39.4

25.

8822

1±

1225

2±

180.

026

5.1

8.39

eH

IJA

SSJ1

218+

460.

079

–0.

012

6.26

–1.

6716

4±

1017

7±

150.

011

5.8

7.69

fdnb

HIJ

ASS

J121

8+47

1.46

31.

233

0.06

845

7.69

540.

169.

9741

7±

444

0±

60.

028

7.6

9.87

ecdi

HIJ

ASS

J121

9+46

0.07

6–

0.00

82.

36–

0.66

34±

647

±9

0.00

76.

67.

38dn

HIJ

ASS

J122

0+45

0.04

8–

0.00

93.

21–

1.25

79±

1811

0±

270.

009

17.1

8.34

fH

IJA

SSJ1

220+

290.

046

–0.

009

10.4

7–

2.31

392

±22

432

±33

0.00

916

.18.

81ci

HIJ

ASS

J122

0+47

0.07

1–

0.01

33.

13–

1.47

49±

1880

±27

0.01

317

.18.

333

HIJ

ASS

J122

0+46

0.22

9–

0.01

536

.51

–1.

9317

3±

1024

3±

150.

009

8.4

8.78

dH

IJA

SSJ1

220+

380.

125

–0.

013

3.51

–0.

9931

±8

53±

120.

011

8.7

7.79

HIJ

ASS

J122

1+45

0.24

8–

0.01

48.

51–

0.60

32±

453

±6

0.00

67.

58.

05dc

HIJ

ASS

J122

1+35

0.07

7–

0.01

13.

29–

1.11

46±

1060

±15

0.01

010

.77.

95H

IJA

SSJ1

222+

320.

146

0.13

30.

019

8.67

9.63

2.61

61±

1489

±21

0.01

816

.48.

79e

HIJ

ASS

J122

2+39

0.06

6–

0.01

12.

90–

1.13

52±

1064

±15

0.01

015

.98.

24n

HIJ

ASS

J122

4+31

0.14

00.

127

0.03

420

.06

22.3

27.

4419

5±

1620

7±

240.

033

17.9

9.23

eH

IJA

SSJ1

224+

390.

059

–0.

012

5.72

–2.

0110

7±

2615

8±

390.

012

15.3

8.50

HIJ

ASS

J122

5+26

0.11

60.

107

0.02

414

.36

15.8

24.

7613

7±

2417

2±

360.

023

5.1

7.98

eci

HIJ

ASS

J122

5+28

0.15

10.

136

0.02

06.

847.

662.

4344

±16

81±

240.

019

6.6

7.90

eH

IJA

SSJ1

225+

450.

052

–0.

009

7.14

–1.

7916

8±

1418

9±

210.

009

17.1

8.69

at Swinburne U




ownloaded from



Tabl

e3

–co

ntin

ued

S pS p

(cor

r)σ

peak

S int

S int

(cor

r)σ

int

w50

±σ

50w

20±

σ20

rms

Dis

tanc

eH

IJA

SSna

me

(Jy)

(Jy)

(Jy)

(Jy

kms−

1)

(Jy

kms−

1)

(Jy

kms−

1)

(km

s−1)

(km

s−1)

(Jy)

(Mpc

)lo

gM

HI

Flag

sa

(B1)

(B2)

(B3)

(B4)

(B5)

(B6)

(B7)

(B8)

(B9)

(B10

)(B

11)

(B12

)(B

13)

HIJ

ASS

J122

5+27

0.43

40.

389

0.02

944

.84

50.2

74.

2612

2±

614

5±

90.

022

10.5

9.12

eH

IJA

SSJ1

225+

333.

067

2.68

10.

139

315.

0335

9.38

7.29

118

±4

138

±6

0.03

74.

79.

28ei

HIJ

ASS

J122

6+31

0.31

00.

278

0.02

874

.183

.04

7.06

354

±14

421

±21

0.02

417

.79.

79ei

HIJ

ASS

J122

6+27

0.04

0–

0.01

02.

40–

1.32

73±

2092

±30

0.01

05.

27.

18f

HIJ

ASS

J122

7+37

0.40

7–

0.02

324

.78

–1.

3364

±4

87±

60.

010

5.0

8.16

dvi

HIJ

ASS

J122

7+43

0.54

6–

0.03

013

.88

–1.

1228

±4

42±

60.

013

2.6

7.34

dbvi

HIJ

ASS

J122

8+22

A0.

069

–0.

010

3.14

–1.

0349

±8

59±

120.

009

8.0

7.67

dfH

IJA

SSJ1

228+

442.

752

–0.

138

250.

36–

2.43

91±

614

2±

90.

015

4.3

9.03

dvi

HIJ

ASS

J122

8+37

0.18

0–

0.01

112

.03

–0.

9769

±8

110

±12

0.00

74.

77.

80dv

iH

IJA

SSJ1

228+

350.

191

0.17

30.

018

5.20

5.79

1.58

29±

1055

±15

0.01

64.

77.

49e5

iH

IJA

SSJ1

228+

430.

498

–0.

027

26.0

4–

1.35

59±

476

±6

0.01

18.

58.

65b

HIJ

ASS

J122

8+22

B0.

243

–0.

016

30.1

8–

2.09

136

±4

153

±6

0.01

18.

78.

73d

HIJ

ASS

J122

8+42

0.06

4–

0.01

02.

04–

0.96

40±

1881

±27

0.01

06.

77.

34fd

HIJ

ASS

J123

0+42

0.09

7–

0.01

211

.09

–2.

0015

1±

1419

2±

210.

011

6.3

8.01

fc5

HIJ

ASS

J123

0+41

2.32

42.

019

0.10

836

1.91

414.

959.

2717

5±

824

1±

120.

038

8.9

9.89

ecd

HIJ

ASS

J123

1+29

0.14

60.

131

0.01

78.

779.

812.

3667

±8

80±

120.

016

9.2

8.29

eH

IJA

SSJ1

232+

390.

140

–0.

012

4.35

–0.

9533

±8

56±

120.

010

10.4

8.04

dbH

IJA

SSJ1

232+

420.

249

0.22

60.

021

16.7

718

.65

2.78

80±

810

1±

120.

018

8.5

8.50

ebH

IJA

SSJ1

232+

370.

233

0.21

10.

024

29.4

32.7

64.

6718

1±

1221

2±

180.

022

7.7

8.66

eH

IJA

SSJ1

232+

310.

610

0.54

30.

034

37.5

42.2

23.

0061

±4

78±

60.

020

4.9

8.37

eiH

IJA

SSJ1

233+

320.

089

0.08

00.

014

5.81

6.49

1.99

73±

1810

9±

270.

013

13.3

8.44

ec5

HIJ

ASS

J123

3+33

0.08

30.

074

0.01

42.

422.

731.

3430

±24

76±

360.

013

12.1

7.97

eH

IJA

SSJ1

233+

240.

068

0.06

00.

015

2.05

2.34

1.59

32±

3280

±48

0.01

518

.48.

27e

HIJ

ASS

J123

3+39

0.10

8–

0.01

13.

26–

0.93

33±

850

±12

0.01

010

.07.

89d

HIJ

ASS

J123

3+30

0.08

10.

075

0.01

48.

689.

552.

5014

9±

2219

5±

330.

013

16.8

8.80

eH

IJA

SSJ1

234+

390.

105

–0.

012

7.85

–1.

6276

±8

92±

120.

011

10.3

8.29

HIJ

ASS

J123

4+35

0.69

20.

617

0.03

666

.77

75.0

73.

3812

2±

413

9±

60.

018

11.8

9.39

eH

IJA

SSJ1

235+

410.

065

–0.

011

1.78

–0.

8931

±12

47±

180.

010

9.4

7.57

HIJ

ASS

J123

5+27

1.56

61.

380

0.07

327

3.75

310.

45.

8724

2±

425

7±

60.

023

11.5

9.99

ecH

IJA

SSJ1

236+

251.

292

1.12

70.

062

272.

7231

1.65

7.36

497

±6

523

±9

0.02

612

.010

.02

eci

HIJ

ASS

J123

6+40

0.17

20.

155

0.02

024

.25

27.1

4.05

190

±10

206

±15

0.01

88.

18.

63e

HIJ

ASS

J123

8+32

0.48

50.

435

0.02

613

.79

15.4

51.

5229

±4

44±

60.

015

3.8

7.73

eiH

IJA

SSJ1

239+

440.

193

0.17

50.

020

7.32

8.14

2.09

38±

855

±12

0.01

88.

98.

18e

HIJ

ASS

J124

0+32

0.07

9–

0.00

85.

58–

1.00

75±

1211

3±

180.

007

11.1

8.21

dfH

IJA

SSJ1

241+

411.

050

0.91

10.

052

110.

6112

6.98

5.22

136

±6

179

±9

0.02

68.

79.

36ec

HIJ

ASS

J124

2+32

1.84

8–

0.09

444

9.62

–3.

9829

8±

432

4±

60.

015

7.3

9.75

cdi

HIJ

ASS

J124

2+38

0.52

20.

469

0.03

623

.65

26.4

83.

4547

±6

62±

90.

027

4.6

8.11

eiH

IJA

SSJ1

243+

240.

047

–0.

010

4.62

–1.

6911

5±

1212

4±

180.

010

25.8

8.86

fH

IJA

SSJ1

243+

322.

050

–0.

103

255.

85–

2.28

134

±6

184

±9

0.01

29.

49.

73cd

HIJ

ASS

J124

4+34

0.24

60.

223

0.01

613

.13

14.6

21.

6558

±4

72±

60.

012

9.0

8.44

eb

at Swinburne U




ownloaded from



Tabl

e3

–co

ntin

ued

S pS p

(cor

r)σ

peak

S int

S int

(cor

r)σ

int

w50

±σ

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the images centred on the central position of HIJASS J1219+46 tothe ones of the lowest H I mass and previously catalogued galax-ies in the sample (see Fig. 4). One might expect that the candidatedwarf galaxy has a similar optical counterpart as the known galaxieswithin the same mass bin – however, as it has not been previouslycatalogued one might also expect it to have lower surface brightnessand thus be less easily visible. All of the lowest H I mass galaxiesshow faint patches of nebulosity in the multicolour SDSS images(Fig. 4). Furthermore, we show HIJASS sources that are newly de-tected in the 21-cm emission line in Fig. 5. These SDSS images arecentred on the H I position and therefore show typical offsets fromthe optical counterparts. For clarification we invert the colours ofthe multicolour SDSS images in Fig. 5 (as opposed to Fig. 4). We donot find a similar galaxy in the images for HIJASS J1219+46 withinthe search radius (the position uncertainty is 1.2 arcmin as given inTable 2). There are multiple galaxies listed in SDSS with no redshiftmeasurements, which match in position to the candidate galaxy/H I

cloud. To determine the optical counterpart(s) and/or confirm theH I cloud accurate position is required from follow-up observations.It is also quite possible that deeper optical imaging is required todetermine any optical counterparts.

In Fig. 6 we show a 1.◦4 × 1.◦4 DSS B-band image of the candi-date galaxy/H I cloud and its surroundings with overlaid H I intensitycontours integrated over the velocity range from 360 to 430 km s−1.HIJASS J1219+46 is a confused source in the DUCHAMP output withHIJASS J1220+46/NGC 4288. The angular separation to NGC4288 is 0.◦3, which corresponds to a distance of ∼40 kpc assumingthat the region lies at a distance of 7.6 Mpc. To the north of HIJASSJ1219+46 lies HIJASS J1218+46 (SDSSJ121811.04+465501.2)and HIJASS J1218+47/M106 (including NGC 4248, UGC 07356and two SDSS galaxies). The angular separation to M106 is0.◦7, which corresponds to ∼93 kpc. Although HIJASS J1219+46lies nearby negative bandpass sidelobes emerging from HIJASSJ1218+47/M106 the GBT follow-up observations confirm the H I

properties measured in HIJASS as given in Table 4 (the GBT andHIJASS spectra are shown in Fig. 5 – the negative bandpass side-lobes are apparent at 220–360 km s−1 in the HIJASS spectrum). Thenature of HIJASS J1219+46 could be tidally stripped gas or a dwarfcompanion.

Wilcots, Lehman & Miller (1996) observed NGC 4288 using theVery Large Array D-configuration ( hereafter VLA D-array; channelwidth of 5.2 km s−1 and a rms noise of 1.0 mJy beam−1) finding agas cloud to the south of NGC 4288 (also see Kovac et al. 2009).Furthermore, the gas cloud shows a tidally disrupted H I stream thatextends well beyond the optical disc of NGC 4288 (Wilcots et al.1996) towards HIJASS J1219+46. However, HIJASS J1219+46lies just outside the area covered by Wilcots et al. (1996) and Kovacet al. (2009).

3.5 Comparison of measured H I parameters with valuesin the literature and follow-up observations

We find 165 H I sources with one or more associate optical coun-terparts as listed in NED and SDSS in the HIJASS data. For H I

detections with one, clear associate counterpart, i.e. H I sourcesthat are not confused (c), not double detections (d) and not in thevicinity of negative bandpass (b) sidelobes (as labelled in this cat-alogue in Section 3.2), we show the position and velocity offsetsfrom our measured H I parameters to previously obtained H I param-eters in Fig. 7. We compare our results to recent literature values:(i) Verheijen & Sancisi (2001) extensively studied 43 spiral galax-ies in the Ursa Major cluster using WSRT, (ii) Springob, Haynes &

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Figure 3. Velocity-integrated H I distribution of the Ursa Major region as obtained from the HIJASS data (grey-scale). The large circle (with radius 7.◦5) drawnin the northern part shows the projected position of the Ursa Major cluster as defined by Tully et al. (1996). Overlaid are symbols to indicate the projectedpositions and sizes of H I detections as presented in this catalogue – open circles indicate H I sources with an associate optical counterpart whereas the filledcircle marks the candidate galaxy/H I cloud, HIJASS J1219+46. This source and the H I detections marked with crosses are newly detected in the 21-cmemission line. Circles surrounded by boxes indicate H I detections for which no central position and no extent (major and minor axis) is measurable.

Giovanelli (2005) have compiled a homogenous sample of H I prop-erties of more than 9000 galaxies from single-dish observations, (iii)Kovac et al. (2009) have conducted a blind H I survey in the CanesVenatici region using the WSRT and (iv) the ongoing ALFALFAsurvey using the Arecibo covers a strip in the southern part of theregion (+24◦ ≤ δ ≤ +28◦) (Haynes et al. 2011). The congruentsample of clear H I sources in this study and the literature includes78 galaxies. The central positions and velocities presented in this

paper are generally consistent with the literature values within theerrors (see Fig. 7).

In Fig. 8 we compare the integrated fluxes measured in HIJASS torecent literature values as well as the GBT follow-up observationslisted in Table 4. We show a comparison of the percentage differenceof integrated fluxes measured in HIJASS to the ones in the literatureand with the GBT (top) as well as the comparison of the absolute fluxvalues for the sample (bottom). The percentage difference is

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Figure 4. Multicolour SDSS images of the lowest H I mass and previously catalogued galaxies with systemic velocities between 300 and 1900 km s−1 togetherwith the HIJASS spectra. The H I masses increase from the left to the right and from the top to the bottom – note that we do not show HIJASS J1218+46 withan H I mass between the ones of HIJASS J1228+22A and HIJASS J1238+32 as it is shown in Fig. 5. The HIJASS name along with the most likely opticalcounterpart (in brackets) is given above each SDSS image and spectrum (including the flags as discussed in Section 3.2). The SDSS images (3.3 × 3.3 arcmin2)are centred on the optical positions of the most likely counterparts. The H I spectra have the optical velocities (cz in km s−1) along the abscissas and the fluxdensities (in Jy) along the ordinates. The H I line emission analysis is conducted within the velocity range as indicated by the dotted vertical lines. The baselinefits to the spectra are conducted within the displayed velocity range excluding the velocity ranges of H I line emission analysis and of other H I sources (e.g.NGC 4393 at ∼650–850 km s−1 in the spectra of HIJASS J1226+27). Note that we show the H I spectra prior to baseline subtraction. Hence, the marked H I

peak flux as well as the 50 and 20 per cent velocity widths slightly vary from the values given in the catalogue as they are measured after baseline subtraction.

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Figure 5. The first-time detections in the 21-cm emission, including the candidate galaxy/H I cloud, HIJASS J1219. We show the inverted multicolour SDSSimages (∼7 × 7 arcmin2) together with the HIJASS and GBT spectra ordered with increasing H I mass (similar to Fig. 4). Left: the SDSS images are centred onthe H I positions. Where available, the optical counterparts that match in position and velocity are marked with boxes. There is no obvious optical counterpartapparent in the SDSS image of HIJASS J1219+46. Right: for comparison, we show the GBT spectrum on top of the HIJASS spectrum (after baselinesubtraction). The spectra have the optical velocities (cz in km s−1) along the abscissas and the flux densities (in Jy) along the ordinates. The velocity rangeof the H I line emissions as well as the negative troughs in the HIJASS spectra of HIJASS J1219+46 (220–360 km s−1 dotted/grey) and HIJASS J1218+46(430–700 km s−1 dotted/grey) are excluded from the baseline fits. HIJASS J1141+32 is further discussed in Section 4.3. Note that we show the spectra ofHIJASS J1219+46 and HIJASS J1138+43 three-point Hanning smoothed.

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Figure 6. Candidate galaxy/H I cloud found in the HIJASS data – HIJASSJ1219+46 (indicated by a cross and labelled in the figure). We show aDSS blue image (1.◦4 × 1.◦4) with overlaid H I intensity contours at 1, 1.5,2, 2.5, 3, 6, 12, 24 and 48 Jy beam−1 km s−1 integrated over the velocityrange from 360 to 430 km s−1. The gridded beam is displayed in the top-leftcorner (FWHM 13.1 arcmin). Galaxies residing in this region are markedwith boxes and some are labelled in the figure.

calculated as follows:

Percentage difference = Sint(HIJASS) − Sint(H I archive, GBT)

Sint(H I archive, GBT)× 100.

Some integrated fluxes differ by more than 20 per cent, in partic-ular in comparison to Kovac et al. (2009). This may be explained asthey use an interferometric data set (obtained with WSRT) whichis not sensitive to diffuse H I emission compared to a single-dishobservation.

There are some data points that lie outside the displayed rangein Fig. 8 (top): HIJASS J1254+27/NGC 4789A with Diff =

219 per cent in comparison with Springob et al. (2005). We finda wide range of literature values for this dwarf irregular galaxy.NGC 4789A has a large H I to optical radius ratio (Hoffman et al.1996), therefore some telescopes may resolve out significant flux.There are two outliers in comparison with the GBT follow-up obser-vations – HIJASS J1218+46/SDSSJ121811.04+465501.2 (Diff =152 per cent) and HIJASS J1145+50/SDSSJ114506.26+501802.4(Diff = 202 per cent). See Fig. 5 for the comparison of the GBTand HIJASS spectra. HIJASS J1218+46 is a double detection withHIJASS J1218+47 including M106, UGC 07356, NGC 4248 andtwo SDSS galaxies (also see Fig. 6). Given that the angular separa-tion between SDSSJ121811.04+465501.2 and M106 is 24.5 arcminand the angular separation between SDSSJ121811.04+465501.2and UGC 07356 is 14.4 arcmin, these galaxies may contribute asignificant amount of flux to the HIJASS detection (FWHM 13.1 ar-cmin) in comparison to the GBT observation (FWHM 9 arcmin).Regarding SDSSJ114506.26+501802.4, the mean signal-to-noiseratio in the HIJASS data is only 1.5 – therefore the rms noise con-tributes significantly to the measured integrated H I flux in compar-ison to the GBT data. In general, this literature comparison showsthat H I properties of galaxies measured with different telescopesand obtained with different parametrization procedures lead to con-sistent results within the errors. However, for H I detections near thedetection limit, the noise can cause fluctuations in the H I measure-ments.

4 D I SCUSSI ON AND RESULTS

4.1 Velocity distribution

The velocity distribution of galaxies residing in the Ursa Majorregion is shown in Fig. 9. The top panel shows the velocity dis-tribution of galaxies as listed in SDSS (white) with spectroscopicredshifts with confidence levels zconf > 0.95 and additional galaxieslisted in NED (grey) with cross-identifications. To avoid duplicateswe cross-correlate the galaxies listed in NED and SDSS within 1 ar-cmin and 50 km s−1 of the central position and velocity. The bottompanel shows the velocity distribution of the H I-selected galaxiesas catalogued in this paper with systemic velocities between 300and 1900 km s−1. The H I detections are colour-coded according toH I sources with associate optical counterparts (in grey) and thepreviously uncatalogued candidate galaxy/H I cloud (in black).

One can see the large-scale structure of the region – the over-density appearing at ∼950 km s−1 in the optical and (less clearly)in the H I-selected sample indicates the presence of the Ursa Majorcluster. There are 212 galaxies listed in SDSS and NED within the

Table 4. The H I properties of newly detected H I sources as measured with the GBT.

vsys ± σ v Sp σ peak Sint σ int w50 ± σ 50 w20 ± σ 20 rmsHIJASS name (km s−1) (Jy) (Jy) (Jy km s−1) (Jy km s−1) (km s−1) (km s−1) (Jy)

(A1) (A5) (B2) (B4) (B5) (B7) (B8) (B9) (B10)

HIJASS J1109+50 905 ± 2 0.049 0.006 4.63 0.36 132 ± 4 146 ± 6 0.005HIJASS J1138+43 1190 ± 2 0.030 0.004 3.22 0.28 155 ± 4 171 ± 6 0.004HIJASS J1141+46 755 ± 3 0.045 0.006 3.24 0.33 75 ± 6 105 ± 9 0.005HIJASS J1141+32 1852 ± 4 0.070 0.008 8.29 0.55 123 ± 8 198 ± 12 0.007HIJASS J1145+50 1663 ± 8 0.015 0.005 0.82 0.27 68 ± 16 105 ± 24 0.005HIJASS J1154+30 972 ± 2 0.045 0.007 2.01 0.31 60 ± 4 72 ± 6 0.006

HIJASS J1209+43B 1061 ± 3 0.049 0.007 2.81 0.38 69 ± 6 90 ± 9 0.007HIJASS J1218+46 398 ± 2 0.047 0.006 2.48 0.30 62 ± 4 75 ± 6 0.006HIJASS J1219+46 390 ± 1 0.061 0.004 2.29 0.14 36 ± 2 56 ± 3 0.003HIJASS J1222+39 1071 ± 2 0.069 0.006 3.71 0.28 59 ± 4 81 ± 6 0.005

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Figure 7. The differences between H I parameters as listed in this paperand previously obtained H I parameters (the used literature is noted in thekey) for H I sources with only one associate optical counterpart within thegridded beam size and the velocity range of the H I source. Top: the positionoffsets; bottom: the systemic velocity offsets – the comparison to Kovacet al. (2009) uses Local Group velocities as discussed in Yahil et al. (1977).

Ursa Major cluster definition by Tully et al. (1996). In this paper wepresent 51 H I detections within the cluster definition by Tully et al.(1996) that contain 96 previously catalogued galaxies. The highnumber of confused detections in our data is due to a high densityof galaxies in the cluster. We will discuss cluster/group member-ship, substructures and HIJASS non-detections in a forthcomingpaper but the number of high-probability cluster members is likelyto increase significantly from the 79 cluster members identified inTully et al. (1996).

There are many groups nearby the cluster, which overlap andmake the cluster difficult to define. In particular foreground galaxygroups with velocities v < 700 km s−1 lead to an asymmetric galaxydistribution in the optical and H I-selected sample. The number ofgalaxies with velocities v > 1300 km s−1 is lower than the number

Figure 8. Comparison of integrated fluxes measured in HIJASS with valuesin the literature and measured with the GBT (follow-up observations): top– deviation of values measured in HIJASS compared to the ones in theliterature and obtained with the GBT; bottom – the integrated flux valuesfrom the literature and the GBT plotted against the ones measured in HIJASS.The used literature is noted in the key. The light coloured markers representpoint sources; the dark ones are for extended sources as listed in the catalogue(Table 3). The solid lines mark the unity relationship and the dashed lines (toppanel) limit the 20 per cent difference in the integrated flux measurements.

Figure 9. Velocity distribution of galaxies residing in the Ursa Major re-gion: top – galaxies as listed in SDSS (white) and additional galaxies listedin NED (grey); bottom – H I-selected galaxies as catalogued in this paperwith an associate optical counterpart coloured in grey whereas the nearbycandidate galaxy/H I cloud is shown in black.

of galaxies residing in the foreground. This may be a selection effector could indicate the filamentary structure: the Ursa Major cluster(at 17.1 Mpc) is connected with the Virgo cluster (at ∼16 Mpc;Mei et al. 2007) via the galaxies and galaxy groups lying at the lowvelocity end.

Fig. 9 also shows one nearby candidate galaxy/H I cloud. We findno candidate galaxies/H I clouds in the Ursa Major cluster, where

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Figure 10. The H I mass histogram of the catalogued sources in this pa-per with systemic velocities between 300 and 1900 km s−1. Grey shadingscorrespond to H I sources with an associate optical counterpart whereas thecandidate galaxy/H I cloud is shown in black.

one might expect to find some e.g. due to previously uncataloguedgas-rich dwarf irregular galaxies or the presence of stripped H I gas.Given that our H I mass limit at the distance of the Ursa Majorcluster is 2.5× 108 M� (assuming a velocity width of 100 km s−1)we cannot rule out candidate galaxies/H I clouds below the H I masslimit.

4.2 H I mass distribution

Fig. 10 shows the H I mass distribution of 151 H I sources as listedin this catalogue (excluded are 15 galaxies with central velocitiesbelow 300 km s−1). H I sources that have been previously detectedand are listed in NED/SDSS are shown in grey whereas the candidategalaxy/H I cloud is presented in black. The latter inhabits the lowH I mass end and is likely to be a dwarf galaxy, i.e. of the samegalaxy population as the previously catalogued galaxies within thesame mass bin. Taylor & Webster (2005) note that ‘dark’ (opticallyinvisible) H I galaxies are unlikely to be detected in our studiedmass range between 107 and 1010.5 M� as the H I gas is normallyassociated with star formation or is destroyed. Meurer et al. (2006)also find that dormant (non-star-forming) galaxies with H I massesabove 3 × 107 M� are very rare. However, high-resolution follow-up observations are required to determine the nature of HIJASSJ1219+46. We discussed the candidate galaxy/H I cloud in moredetail in Section 3.4. We note that we did not find a numerouslow-mass population of gas-rich dwarf galaxies to solve the dwarfdeficiency problem as discussed in Trentham et al. (2001).

We can place an upper limit on the H I mass for the galaxies listedin NED/SDSS within the Ursa Major region, which we did not detectin HIJASS. The survey sensitivity is 2.5 × 108 M� (assuming avelocity width of 100 km s−1 and a distance of 17.1 Mpc). A lowerH I mass limit is valid for galaxies lying in the foreground groupsand filamentary structure (with v < 700 km s−1 and distances D< 17.1 Mpc), whereas for background galaxies (v > 1200 km s−1)with distances D > 17.1 Mpc a slightly higher H I mass limit isappropriate (as MH I = 8.38 × 105 × D2).

4.3 Candidates for galaxy–galaxy interactions

In this paper, there are 54 H I detections (33 per cent) which havetwo or more optical counterparts as listed in NED/SDSS within thegridded beam size and within the velocity range of the H I detection(see H I detections labelled with ‘c’ in the catalogue in Section 3.2).We cannot clearly associate the H I content with only one opticalcounterpart. However, these H I detections with multiple opticalcounterparts are intriguing objects as galaxy–galaxy interactionsmight take place due to the small separation between the galaxies(e.g. 10 arcmin corresponds to 50 kpc at a distance of 17.1 Mpc).

For example, HIJASS J1141+32 encompasses four previ-ously known dwarf galaxies within 1700 and 1900 km s−1

(see Fig. 11): Mrk 0746, KUG 1138+327, WAS 28 andSDSSJ114135.98+321654.0 (which has no cross-identification inNED and is therefore not listed in our catalogue) – there are no pre-vious detections in the 21-cm emission line for any of these galaxies.High-resolution follow-up observations are required to study the H I

distribution, kinematics and possible interaction of these galaxies.HIJASS J1220+29 encompasses three previously catalogued

galaxies (see Fig. 11) at 610–710 km s−1, namely NGC 4278 (ellip-tical), SDSSJ122005.73+291650.0 (spiral) and NGC 4286 (spiral)(ordered with increasing angular separation from the central H I po-sition). Morganti et al. (2006) have conducted a WSRT observationof NGC 4278, NGC 4286 and SDSSJ122005.73+291650.0 – theobservations reveal two tail-like structures west and south-west ofNGC 4278.

Out of the 54 confused HIJASS detections, 33 galaxies appearto have dwarf companions. This leaves us with 21 high-probabilitycandidates for galaxy–galaxy interactions of which 11 HIJASS de-tections (52 per cent) are within the Ursa Major cluster as definedby Tully et al. (1996). It is remarkable that the Ursa Major clus-ter as defined by Tully et al. (1996) only comprises approximately12 per cent of the surveyed volume discussed in this paper but con-tains about half of all high-probability candidates for galaxy–galaxyinteractions. This is also the case (48 per cent) if we include twonearby DUCHAMP double detections, i.e. we do not only considergalaxies within the gridded beam (as the physical size of the beamis smaller for nearby regions) but also merged H I detections as can-didates for high-probability galaxy–galaxy interactions. Verheijen& Sancisi (2001) have observed 10 of the high-probability candi-dates for galaxy–galaxy interactions in the Ursa Major cluster. Thesample includes the most massive galaxy (Messier109), the largest(NGC 3718) and some of the brightest systems (NGC 4026, NGC4111 and NGC 4088).

According to Verheijen & Sancisi (2001) the interacting systemsare as follows. (i) NGC 3769 is strongly interacting with its dwarfcompanion NGC 3769A. (ii) NGC 3893 is an interacting pair withNGC 3896. (iii) Some tidal debris can be seen in the interactingpair IC 0750 and IC 0749. (iv) The largest galaxy in the cluster –NGC 3718 – shows distorted morphology and may be interactingwith NGC 3729. (v) NGC 4088 is one of the brightest systems inthe Ursa Major cluster with ongoing vigorous star formation. Thesystem is strongly disturbed and in close vicinity of NGC 4085. (vi)The NGC 4111 and (vii) NGC 4026 groups are also known to beinteracting and discussed in more detail in Section 4.4.

Three of the high-probability candidates – namely NGC 3917,Messier109 and NGC 4157 – do not show any signs of interactionswith their dwarf companions (Verheijen & Sancisi 2001).

Verheijen & Sancisi (2001) find further interacting galaxypairs: NGC 3949 may be interacting with a small companion(SDSSJ115340.69+475156.4) and UGC 06818 may be tidally

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Figure 11. Two candidate regions for galaxy–galaxy interactions are shown with DSS2 B-band images (1◦ × 1◦) and overlaid integrated flux levels (contours)starting at ±1.5 Jy beam−1 km s−1. Negative contour levels are indicated with dashed lines. The gridded beam size is indicated in the bottom-left corner ofeach image. Left: HIJASS J1141+32 – there are four dwarf galaxies at approximately 1700–1900 km s−1 as indicated by boxes and labelled in the figure. Theincrement of the contour levels is 2 Jy beam−1 km s−1. Right: HIJASS J1220+29 – the NGC 4278 group at approximately 400–850 km s−1. The contour linesinclude three previously catalogued galaxies as listed in NED (marked with boxes and labelled in the figure) and increase with 1 Jy beam−1 km s−1. We alsoshow three galaxies (at similar velocities as the NGC 4278 group) that are not detected in HIJASS (triangles).

interacting with a faint companion – these systems are not includedin our sample of high-probability candidates for galaxy–galaxy in-teractions as they include interactions with dwarf companions. Notethat we quote UGC 06818 as a clear single detection in our cata-logue – there are no galaxies listed in close vicinity of UGC 06818in NED/SDSS with know redshifts. Verheijen & Sancisi (2001) alsofind NGC 3998 with disturbed H I content, which lies just outsidethe HIJASS data cubes at Dec. δ 55◦27′13′′.

4.4 HIJASS detections with extended H I envelopes

We find two H I detections with extended H I envelopes that do nothave previously catalogued galaxies within the H I extension.

Within the Ursa Major cluster lies the H I extension/plume in theNGC 4026 group (see Fig. 12), which has already been studiedby Appleton (1983; Jodrell Bank), van Driel et al. (1988; WSRT)and Verheijen & Zwaan (2001; VLA D-array). Six galaxies arelisted in NED with heliocentric velocities 700 ≤ v ≤ 1100 km s−1,four of which are included in the H I envelope (boxes) and two ofwhich are in vicinity of the H I extensions (triangles; non-detectionin HIJASS). The WSRT observations reveal an H I filament atα 11h58m57s and δ 50◦46′42′′ with a systemic velocity of∼960 km s−1 (van Driel et al. 1988). The H I filament measures ap-proximately 38 kpc in size (which corresponds to ∼7.5 arcmin atthe distance of 17.1 Mpc) and contains 2.1 × 108 M�. Further-more, van Driel et al. (1988) determine the H I mass of NGC 4026as ≤0.71 × 108 M�, that of UGC 06956 as 5.1 × 108 M�, that ofUGC 06922 as 4.9 × 108 M� and that of UGC 06917 as 1.28 ×109 M�. We detect NGC 4026, UGC 06956 and the H I filamentcombined in HIJASS J1158+50 and we measure an H I mass of7.94 × 108 M� – this matches the total H I mass measured by vanDriel et al. (1988) within 1 per cent. Regarding UGC 06922 andUGC 06917, we measure an H I mass of 6.17 × 108 and 1.58 × 109

M�, respectively. One may expect to measure a larger H I flux usinga single-dish telescope compared to van Driel et al. (1988) using

WSRT. However, the H I content of UGC 06922 is likely confusedas UGC 06956 lies in close vicinity.

High-resolution observations of this system conducted with theVLA D-array (Verheijen & Zwaan 2001) reveal an H I filament of∼97 kpc in size (which corresponds to ∼18 arcmin and indicatedby a cross in Fig. 12). The origin of the H I filament is likely to betidally stripped gas of NGC 4026. Verheijen & Zwaan (2001) notethat all three bright lenticular galaxies in the Ursa Major clusterincluding NGC 4026 have disturbed H I.

Another intriguing H I extension in the Ursa Major cluster isseen in the NGC 4111 system, which has already been studied byVerheijen & Zwaan (2001; VLA D-array). There are six previouslycatalogued galaxies as listed in NED within 20 arcmin angular sep-aration and within 150 km s−1 of the central H I velocity (see Fig.12). NGC 4111 is also one of the three brightest lenticular galaxiesin the Ursa Major cluster with disturbed H I (Verheijen & Zwaan2001). The H I extends approximately 122 kpc (which correspondsto ∼28 arcmin at the distance of 15.0 Mpc; Tully et al. 2009 and in-dicated by a cross in Fig. 12) south of the projected central positionof NGC 4111 (Verheijen & Zwaan 2001). Furthermore, the dis-turbed H I connects NGC 4111 with its close neighbouring galaxiesNGC 4117 and NGC 4118.

The third of the brightest lenticular galaxy in the Ursa Majorcluster with disturbed H I content according to Verheijen & Zwaan(2001) – NGC 3998 – lies just outside the HIJASS data cubes atDec. δ 55◦27′13′′.

We do not find any H I detections with extended H I envelopesoutside the Ursa Major cluster as defined by Tully et al. (1996).

4.5 Comparison to large area blind H I surveys

Blind H I surveys have the potential for detecting previously un-catalogued galaxies and H I clouds. The two largest blind H I sur-veys to date are HIPASS (Staveley-Smith et al. 1996; Barnes et al.2001; Koribalski et al. 2004; Meyer et al. 2004) and ALFALFA

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Figure 12. Two Ursa Major subregions with extended H I content. We show DSS2 B-band images (1.◦3 × 1.◦3) with overlaid H I intensity contours at ±1.5,3, 6 and 12 Jy beam−1 km s−1. Negative contour levels are indicated with dashed lines. The beam (13.1 arcmin) is indicated in the bottom-left corner of eachimage. Left: the NGC 4026 group at approximately 800–1050 km s−1. The contour lines include four catalogued galaxies as indicated by boxes and labelled inthe figure. The galaxies marked with triangles, UGC 06992 and SDSSJ115950.83+502955.0, are below the H I sensitivity of this catalogue. The H I filamentis indicated by a cross – the extent of the H I filament is similar to the cross size. Right: the NGC 4111 group at approximately 650–950 km s−1. The contourlines include six previously catalogued galaxies as listed in NED (marked with boxes and labelled in the figure). The disturbed H I content of NGC 4111 andits extent is indicated by a cross. We also show two galaxies (at similar velocities than the NGC 4111 group) that are not detected in HIJASS (triangles). Wenote that UGC 07146 (in the top-left corner) is detected for the first time in the 21-cm emission line (with a systemic velocity of 1057 km s−1 and thereforeoutside the displayed velocity range).

(Giovanelli et al. 2005; Haynes et al. 2011). While the HIPASScatalogues contain numerous sources without optical or infraredcounterpart (e.g. in regions of high Galactic extinction), there is noevidence for any optically dark galaxies (Ryan-Weber et al. 2002;Koribalski et al. 2004). One of the most massive starless H I cloudsis HIPASS J0731−69 (MH I ∼ 109 M�; Ryder et al. 2001). It islocated near the asymmetric spiral galaxy NGC 2442 in the NGC2434 group. A possible scenario for its origin is discussed in Bekkiet al. (2005). Australia Telescope Compact Array (ATCA) observa-tions by Ryder & Koribalski (2004) reveal several H I clumps thatare probably embedded in a common envelope of diffuse H I. Agroup of H I clouds found around 400 km s−1, including HIPASSJ1712−64 (Kilborn et al. 2000), HIPASS J1718−59 and HIPASSJ1616−55 (Koribalski et al. 2004), are likely tidal debris relatedto the Magellanic Clouds and the Leading Arm. In areas of highstellar density and dust obscuration, it can be difficult to detect op-tical or infrared counterparts to H I-detected galaxies. Apart fromthe Galactic plane, other sources — like the Magellanic Clouds –may hide the stellar component of galaxies. An example is HIPASSJ0546−68 (vsys = 1306 km s−1) behind the Large Magellanic Cloud(Ryan-Weber et al. 2002).

The ALFALFA 40 per cent survey has detected nearly 16 000H I sources in the velocity range from −470 to ∼18 000 km s−1

(Haynes et al. 2011); among these are 1013 sources with-out assigned optical counterparts. Of the latter, 814 are at ve-locities from −470 to ∼340 km s−1, i.e. likely to be High-Velocity Clouds (HVCs). The remaining are H I cloud candi-dates, with ∼75 per cent located near galaxies of similar red-shifts (e.g. Leo Ring; Stierwalt et al. 2009). About 50 candidates(0.3 per cent) for isolated H I clouds remain; these require follow-up optical and interferometric H I observations to identify theirnature.

In our survey of the Ursa Major region we were able to confirmjust one H I source without a definite optical counterpart (HIJASSJ1219+46; vsys ∼ 392 km s−1). It is located near the peculiar galaxyNGC 4288 (HIJASS J1220+46; vsys ∼ 520 km s−1; also see Wilcotset al. 1996; Kovac et al. 2009) in the Canes Venatici region. This H I

source is discussed in more detail in Section 3.4. The nature of thisH I source could be a dwarf companion or tidally stripped gas. H I

imaging and deep optical follow-up will be required to determinethe true nature.

5 SU M M A RY

The first blind H I survey of the Ursa Major region was conductedin 2001–02 as part of HIJASS. The nearby Ursa Major region iswithin a velocity range from 300 to 1900 km s−1 and covers anarea of ∼480 deg2. Using the automated source finder DUCHAMP

we identify 166 H I sources in the data based on their peak fluxdensity. The measured H I properties of the sources are presented ina comprehensive catalogue. We address the catalogue completenessand reliability – we find that the catalogue is 95 per cent completeabove our peak flux density cut (33 mJy). The H I mass limit of thecatalogue is 2.5 × 108 M� (assuming a velocity width of 100 km s−1

and a distance of 17.1 Mpc).The catalogue includes 165 H I sources for which optical counter-

parts are identified using NED and SDSS. We find multiple counter-parts within the gridded beam for 33 per cent of the H I detections,which are candidates for galaxy–galaxy interactions. There are 21high-probability interacting systems – about half of these are withinthe Ursa Major cluster and have been studied by Verheijen & Sancisi(2001). It is remarkable that the Ursa Major cluster as defined byTully et al. (1996) only comprises approximately 12 per cent of thesurveyed volume discussed in this paper but contains about half of

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all high-probability candidates for galaxy–galaxy interactions. Wediscuss four examples of interacting systems, two of which showintriguing extended H I content. The latter have been already beenstudied with higher resolution and revealed H I filaments and H I

distortions of the bright lenticular galaxies.The HIJASS data contain 10 H I sources that are newly detected

in the 21-cm emission line. One of these does not have a visible as-sociate optical counterpart and is likely to be a candidate galaxy/H I

cloud. This previously uncatalogued H I source requires follow-upobservations to investigate its nature.

AC K N OW L E D G M E N T S

We thank the HIJASS team for providing the data. HIJASSwas funded by the UK PPARC (Grant No. PPA/G/S/1998/00620to Cardiff). We also acknowledge the UK PPARC (Grant No.GR/K28237 to Jodrell Bank) that funded the multibeam receiv-ing system at Jodrell Bank. We thank David Barnes and MarkCalabretta for their help with the fake source injection into the rawdata. We thank Felix James ‘Jay’ Lockman for his help with theGBT follow-up observations from setting up, execution to the datareduction. We thank Emma Ryan-Weber, Glenn Kacprzak and theanonymous referee for useful comments. This research has madeuse of the NASA/IPAC Extragalactic Database, which is operated bythe Jet Propulsion Laboratory, California Institute of Technology,under contract with the National Aeronautics and Space Admin-istration. Digitized Sky Survey material is acknowledged, whichwas produced at the Space Telescope Science Institute under USGovernment grant NAG W-2166. This research has also made useof the Sloan Digital Sky Survey (SDSS). Funding for the SDSSand SDSS-II was provided by the Alfred P. Sloan Foundation, theParticipating Institutions, the National Science Foundation, the USDepartment of Energy, the National Aeronautics and Space Admin-istration, the Japanese Monbukagakusho, the Max Planck Society,and the Higher Education Funding Council for England. The SDSSwas managed by the Astrophysical Research Consortium for theParticipating Institutions.

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