(Genzel et al, ApJ 1998; Lutz et al, ApJ...

ULIRGsULIRGs: Results from ISO : Results from ISO ((GenzelGenzel et al, et al, ApJApJ 1998;1998;

Lutz et al, Lutz et al, ApJApJ 1998)1998)

Thomas OberstThomas OberstFebruary 22, 2006February 22, 2006

A671A671

Composite image of high-luminosity colliding starburst galaxies (=ULIRGS) in the early Universe (z not given, probably ~1); Red = 7µm ISO, blue = 2µm 2.2m Hawaii Telescope. 3’ x 3’ field of view in Lockman Hole in Ursa Major. ESA website

February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by ISOT. Oberst, A671: ULIRGs by ISO 22

Infrared Space Observatory (ISO)Infrared Space Observatory (ISO)60 cm primary 60 cm primary Ritchey-Chrétien telescope built by ESA Bio:Bio:–– Launched into highly elliptical Earth orbit Nov. 1995; 2300L lLaunched into highly elliptical Earth orbit Nov. 1995; 2300L l--HeHe–– Highly successful & diverse campaignHighly successful & diverse campaign

Cassiopeia A Supernova (Cassiopeia A Supernova (LagageLagage A&A ‘96)A&A ‘96)Planet formation from dying stars (Waters Nature ‘98)Planet formation from dying stars (Waters Nature ‘98)First detection of a First detection of a protostellarprotostellar core, L1689B (Redman RAS ‘02)core, L1689B (Redman RAS ‘02)Detection of intergalactic dust (Detection of intergalactic dust (StickelStickel IAU Symposium ‘03)IAU Symposium ‘03)Comet HaleComet Hale--BoppBopp ((GrGrüünn A&A ‘03)A&A ‘03)ULIRGsULIRGs ((GenzelGenzel ApJApJ ‘98)‘98)MIRMIR--FIR spectra for large number of sourcesFIR spectra for large number of sources

–– switched off & burned in atmosphere May 1998switched off & burned in atmosphere May 1998Wavelength range 2.5 Wavelength range 2.5 –– 240 240 µµmm


ISO InstrumentsISO Instruments–– LongLong--Wavelength Spectrometer (LWS): FP & gratingWavelength Spectrometer (LWS): FP & grating–– ShortShort--Wavelength SpectrometerWavelength Spectrometer (SWS): (SWS): FP &FP & grating grating –– Imaging Imaging PhotopolarimeterPhotopolarimeter (ISOPHOT): two gratings(ISOPHOT): two gratings–– Camera (ISOCAM)Camera (ISOCAM)

2.47 - 4.87 & 5.84 - 11.62 µm; R ~ 100

2.38 – 45.2 µm; R ~ 1000 - 2000

(of interest for Genzel ’98)


ISO vs. IRASISO vs. IRASISO has …– Wider wavelength coverage (~ 2.5 – 240 µm continuous vs. four

bands covering ~ 7 – 140 µm)– better spatial resolution (1.5” – 90” vs. 4’ – 6’)– Greater sensitivity (up to x1000)– more sophisticated instrumentation, esp. for spectroscopy – longer lifetime (~30 vs. ~10 months)

ISO IRAS


GenzelGenzel et. al. et. al. ApJApJ 19981998

Not the first ISO paper on ULIRGSNot the first ISO paper on ULIRGS– Arp 220, NGC 6240 and NGC 3256: Lutz et. al. A&A 1996Lutz et. al. A&A 1996–– ArpArp 220: Sturm et. al. A&A 1996220: Sturm et. al. A&A 1996

But was the first “comprehensive” ISO ULIRG paperBut was the first “comprehensive” ISO ULIRG paper–– ISO Spectroscopy on 15 ISO Spectroscopy on 15 ultraluminousultraluminous IRAS galaxies (LIRAS galaxies (L88--10001000µµmm ≥≥

10101212 LL ))–– Compared with ISO and literature data on 30 starburst and AGN Compared with ISO and literature data on 30 starburst and AGN

template galaxiestemplate galaxies–– Placed earlier ISO ULIRG papers on more secure statistical Placed earlier ISO ULIRG papers on more secure statistical

footingfooting–– Lengthy background and theory discussions (27 page article!)Lengthy background and theory discussions (27 page article!)

Later papers went ever further: Lutz et. al. Later papers went ever further: Lutz et. al. ApJApJ ’98 looks at 60 ISO ’98 looks at 60 ISO ULIRGS (4½ page article) ULIRGS (4½ page article)


SWS SpectraSWS Spectra Y-axis = Flux density (Jy); X-axis = velocity (+/- 1000 km/s); error bars = 1s (Fig. 1, Genzel ‘98)


SWS Spectra (2)SWS Spectra (2) Y-axis = Flux density (Jy); X-axis = velocity (+/- 1000 km/s); error bars = 1s (Fig. 1, Genzel ‘98)


ISOPHOT SpectraISOPHOT Spectra (Fig. 2, Genzel ‘98)


Data ValuesData Values (Table 1, Genzel ‘98)

Strength of 7.7µm PAH feature: ratio of peak of 7.7 µm flux to 7.7 µm continuum as obtained with a linear interpolation between 5.9 and 11.0 µm on ISOPHOT

Br α (4.05µm) and Br β (2.63µm) H recombination lines from SWS


Spectral Line Probes Spectral Line Probes (UV(UV--irradiated ionized gas)irradiated ionized gas)

NeNe++, S, S++++, O, O++++++, and Ne, and Ne4+4+ (21(21--97eV) all arise in HII 97eV) all arise in HII regions regions photoionizedphotoionized by stars or an AGN (or fast ionizing by stars or an AGN (or fast ionizing shocks)shocks)SiSi++ (8.2 (8.2 eVeV) arises either in HII regions or PDR regions ) arises either in HII regions or PDR regions between HII regions and molecular cloudsbetween HII regions and molecular cloudsS[III] 18.7 / 33.5 S[III] 18.7 / 33.5 µµm m →→ electron densityelectron density–– For observed galaxies, For observed galaxies, nnee ~ 10~ 1022 –– 10102.52.5 cmcm--33

O[IV] 25.9 / O[IV] 25.9 / Ne[IINe[II] 12.8 ] 12.8 µµm & m & Ne[VNe[V] 14.3 / ] 14.3 / Ne[IINe[II] 12.8 ] 12.8 µµm m →→ hardness of ionizing UV field (effective T)hardness of ionizing UV field (effective T)–– O[IV] generally stronger (more significant) than O[IV] generally stronger (more significant) than Ne[VNe[V] ]

detectiondetection


Spectral probes (2)Spectral probes (2) SWS Line Ratios; IRAS 15250 & 19254 excluded due to poor Ne[V] and O[IV] detections (Fig. 3, Genzel ‘98)

~ x10-102difference ~ x10-102

difference


PAH probesPAH probes(UV(UV--irradiated hot dust)irradiated hot dust)

PAHsPAHs arise in arise in PDRsPDRs or in diffuse HI regionsor in diffuse HI regionsClassical study of 60 galaxies of different types Classical study of 60 galaxies of different types ⇒⇒ PAHsPAHsare prominent in starburst galaxies but faint or absent in are prominent in starburst galaxies but faint or absent in AGNsAGNs (Roche et. al. MNRAS 1991)(Roche et. al. MNRAS 1991)–– ⇒⇒ PAH strength may be useful for distinguishing PAH strength may be useful for distinguishing

between starburst and AGNbetween starburst and AGN–– Is insensitive to extinction as long as 7 Is insensitive to extinction as long as 7 µµm continuum m continuum

is affected same as emission featuresis affected same as emission featuresGenzelGenzel template galaxies are in excellent agreement template galaxies are in excellent agreement with Roche studywith Roche study


PAH Probes (2)PAH Probes (2)

“Composite” sources with AGN + star formation contribution

~ x10

(Fig. 4, Genzel ‘98)


AGN or Starburst? … AGN or Starburst? … UVUV--irradiated ionized gas vs. UVirradiated ionized gas vs. UV--irradiated hot dustirradiated hot dust

“Mixing Model”

(Fig. 5, Genzel ‘98)


GenzelGenzel ConclusionsConclusionsOn average:On average:–– 2020--30% of 30% of ULIRGsULIRGs are AGN dominatedare AGN dominated–– 7070--80% of 80% of ULIRGsULIRGs are starburst dominatedare starburst dominated

~ ½ of sources probably have simultaneously an AGN ~ ½ of sources probably have simultaneously an AGN and starburst activity in a 1and starburst activity in a 1--2 2 kpckpc diameter diameter circumnuclearcircumnuclear diskdisk


Lutz et. al. Lutz et. al. ApJApJ 1998: Average Spectrum1998: Average Spectrum

Average ISOPHOT spectrum of 60 ULIRGs, individually scaled such that net flux = 1 Jy; dotted lines on upper plots show additional AV=50 foreground extinction (Fig. 1, Lutz ‘98)

⇒ “ULIRGs are, on average, starburst-like”


Lutz ’98: Lutz ’98: PAHsPAHs vs. Spectral Linesvs. Spectral Lines

PAH strength vs. ratio of ISO 5.9µm continuum to IRAS 60µm continuum.

• Dilution = less PAH compared to 60µm continuum due to increasing hot dust

•Destruction = of PAHs

(Fig. 3, Lutz ‘98)

Dotted = dilutionDashed = mixing model ⇒ 80% of ULIRGs

predominantly powered by star formation


Lutz ’98: Lutz ’98: PAHsPAHs vs. Luminosityvs. Luminosity

(Fig. 2, Lutz ‘98)⇒ Fraction of ULIRGspowered by AGN increases with luminosity


Lutz ’98: MergersLutz ’98: Mergers

Plot of ISO PAH strength vs. nuclear separation in ULIRGsas discerned by pre-ISO NIR imaging observations

(Fig. 4, Lutz ‘98)

Starbursts found to nearest separations ⇒ no correlation between merger status and AGN strength


Lutz ConclusionsLutz Conclusions80% of 80% of ULIRGsULIRGs are predominantly powered by star are predominantly powered by star formationformationHowever the fraction of However the fraction of ULIRGsULIRGs powered by AGN powered by AGN increases with luminosityincreases with luminosity–– 15% when 15% when LLbolbol < 2 x 10< 2 x 101212 LL–– >50% when >50% when LLbolbol > 2 x 10> 2 x 101212 LL

For For ULIRGsULIRGs for which IR images are available to for which IR images are available to determine their merger status, there are no conclusive determine their merger status, there are no conclusive results on whether advanced mergers are more AGNresults on whether advanced mergers are more AGN--like, as evolutionary models suggestlike, as evolutionary models suggest


ReferencesReferencesESA websiteESA websiteGenzelGenzel et. al., “What Powers et. al., “What Powers UltraluminousUltraluminous IRAS IRAS Galaxies?”, The Astrophysical Journal, 498:579Galaxies?”, The Astrophysical Journal, 498:579--605, 605, May 10, 1998.May 10, 1998.Lutz et. al., “The Nature and Evolution of Lutz et. al., “The Nature and Evolution of UltraluminousUltraluminousInfrared Galaxies: a MidInfrared Galaxies: a Mid--Infrared Spectroscopic Survey”, Infrared Spectroscopic Survey”, The Astrophysical Journal, 505:L103The Astrophysical Journal, 505:L103--L107, October 1, L107, October 1, 1998.1998.Personal correspondence with Steve HaileyPersonal correspondence with Steve Hailey--DunsheathDunsheathand and YanlingYanling Wu Wu

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