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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
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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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 33
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)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 44
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 55
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)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 66
SWS SpectraSWS Spectra Y-axis = Flux density (Jy); X-axis =
velocity (+/- 1000 km/s); error bars = 1s (Fig. 1, Genzel ‘98)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 77
SWS Spectra (2)SWS Spectra (2) Y-axis = Flux density (Jy);
X-axis = velocity (+/- 1000 km/s); error bars = 1s (Fig. 1, Genzel
‘98)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 88
ISOPHOT SpectraISOPHOT Spectra (Fig. 2, Genzel ‘98)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 99
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1010
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1111
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1212
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1313
PAH Probes (2)PAH Probes (2)
“Composite” sources with AGN + star formation contribution
~ x10
(Fig. 4, Genzel ‘98)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1414
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)
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1515
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1616
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”
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1717
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1818
Lutz ’98: Lutz ’98: PAHsPAHs vs. Luminosityvs. Luminosity
(Fig. 2, Lutz ‘98)⇒ Fraction of ULIRGspowered by AGN increases
with luminosity
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 1919
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 2020
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
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February 22, 2006February 22, 2006 T. Oberst, A671: ULIRGs by
ISOT. Oberst, A671: ULIRGs by ISO 2121
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