The LALA Survey

The LALA Survey

Rhoads et al. 2000

Subaru and Supreme

Taniguchi et al. 2004

Blind spectroscopy searches•Martin et al. 2006: ultra-sensitive spectroscopic survey of Ly emitters at z~5.7

•Multi-slit windows technique complements other emission-line surveys.

•Narrow-band imaging surveys cover large areas of sky but only detect much brighter objects. Long-slit spectra taken along cluster caustics yield intrinsically fainter lensed Ly emitters but probe small volumes of space.

•To a line flux limit of a few times 10^-18 erg/s/cm^2, we found 150 emission-line sources with no detectable continuum.

•These candidates are being re-observed with broad spectral coverage to determine the line identity. To date, the interloper to Ly ratio is about 8:1.

•The sky positions of the Ly candidates generally do not coincide with those of foreground objects in ultra-deep r band or i' images -- consistent with the presence of a strong Lyman break.

Blind spectroscopy searches

Lysurvey to constraints reionization

Malhotra et al. 2006

The observed number density of Ly sources at z~6.5 implies a minimum volume of the intergalactic medium that must be ionized, in order to allow the Ly photons to escape attenuation.

Volume estimated by assigning to each Ly emitter the minimum ionized bubble that would allow half its Ly photons to escape.

This implies a lower limit to the ionized gas volume fraction of 20%-50% at z=6.5.

This limit is completely independent of what ionizing photon sources produced the bubbles.

Deeper Ly surveys are possible with present technology and can strengthen these limits by detecting a higher density of Ly galaxies.

Ly Surveys: Implications for Galaxy FormationDawson et al. 2004

Keck low resolution optical spectra of 17 Ly galaxies and one Lyman break galaxy at z~4.5 discovered in the Large Area Lyman Alpha survey (LALA).

Sample of ~350 candidate Ly galaxies at z~4.5 in a search volume of 1.5×106 comoving Mpc3.

Targeted 25 candidates for spectroscopy; the 18 confirmations suggest a selection reliability of 72%.

The large rest equivalent widths (median W ~80 Å) but narrow physical widths (Deltav<500 km

s-1) of the Ly emission lines, and the lack of accompanying high-ionization emission lines, suggest that these galaxies are young systems powered by star formation rather than by AGN.

Theoretical models of galaxy formation suggest that a small fraction of Ly galaxies at z~4.5 may still be nascent, metal-free objects. Indeed, we find with 90% confidence that three to five of the confirmed sources show W >240 Å, exceeding the maximum predicted for normal stellar

populations. Nonetheless, we find no evidence for HeII 1640 emission in either individual or composite spectra, indicating that although these galaxies are young, they are not truly primitive, Population III objects.

Ly Surveys: z~7

Galaxies at z~9?

Willis & Courbin 2005

Lya Surveys: Searching for First Light

Near-IR search for galaxies At z=9.17Mannucci et al. 2006

Lya Surveys: Searching for First Light

Mannucci et al.

Emission Line SurveysLecture 4

Mauro GiavaliscoMauro Giavalisco

Space Telescope Science InstituteSpace Telescope Science Institute

University of Massachusetts, AmherstUniversity of Massachusetts, Amherst11

11From January 2007From January 2007

Ly searches to complement continuum ones

Steidel et al. 1999

Finding high-redshift galaxies:color selection

B435 V606 z850

Unattenuated Spectrum Spectrum

Attenuated by IGM

B435 V606 i775 z850

z~4

1. Color selection is very efficient in finding galaxies with specific spectral types in a pre-assigned redshift range

2. Wide variety of methods available, targeting a range of redshifts, galaxies’ SEDs:• Lyman and Balmer break

(Steidel, Adelberger, MG)• DRG (Franx, Labbe et al.)• BzK (Daddi et al.)• Photo-z (Mobasher et al)

Here, the case of “Lyman-break galaxies” GOODS yielded the deepest and

largest quality samples of LBGs at z~4 to ~6 (7?)

Color selection at z>3B-band dropouts: 3.5<z<4.5

Vanzella et al. 2006

Color selection at z>3 V-band dropouts: 4.5<z<5.5

Color selection at z>3i-band dropouts: 5.5<z<6.5

Color selection at z>3z-band dropouts: 6.5<z<7.5

The Redshift Distribution

#183

#27

LBGs at z>3 are targets of the ongoing GOODS spectroscopic time with the ESO VLT and Keck

Vanzella et al. 2005, 2006 in prep.Stern et al. 2006 in prep.Giavalisco et al. 2004; 2006, in prep.


Steidel et al. 1999


Steidel et al. 1999

Other important works by:Hu et al. 2001Ouchi et al. 2004Taniguchi et al. 2004

At faint end of LF, Ly emitters might dominate the LFSFD underestimated by as much as 2x


Results from the GOODSsurvey (Giavalisco et al. 2004)


What is causing the difference in the spectra?

Abs.Em.

“Absorbers” tend to be redder than emitter.

However, there are blue “absorbers”, too.

No strong correlation of spectral “types” with the ellipticity of the galaxies.

Are these disks?

Possibly an effect of geometry of gas and dust, metallicity and age (see Shapley et al. 2004).

Color selection at z~2: BzK galaxies

BzK selection well suited for 24m MIPS studies:• Selected range 1.4 < z < 2.5 places strong mid-IR features in 24m band• Color selection includes objects with red UV continuum, e.g., from extinction• K-band selection suitable for relatively massive galaxies

(Daddi et al. 2005)

BzK selection: 1.4<z<2.5

The LALA Survey

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