Mid-IR selection of Ultra-Luminous Far-IR Galaxies

Starburst and AGN tracers in z~2 ULIRGs continuum & CO mm emission, radio and PAH

Alain Omont (IAP, CNRS and Université Paris 6)

OUTLINE

Mid-IR luminous Ultra-Luminous Far-IR Galaxies

Submillimeter galaxies: high-z Ultra-Luminous Far-IR Galaxies

24µm bright z~2 ULIRGs: AGN vs PAHs/starburst

Mm continuum emission. Far-IR luminosity, star formation rate

Radio emission: starburst/AGN

CO mm emission. Molecular gas, structure and dynamics

Stellar mass

Sructure (HST, radio, CO): merger/outflow

Prospects (Herschel, ALMA, JWST)

Collaborators: C. Lonsdale, M. Polletta, N. Fiolet, A. Beelen, A. Baker, F. Owen, S. BertaL. Yan, L. Tacconi, D. Lutz, A. Sajina , G. Lagache, D. ShupeJ. Huang, J. Younger, G. Fazio, etc.

Reminder

SMGs: strongest starbursts in the UniverseEssential steps of star formation in massive galaxies at z >~ 2

Revealed by SCUBA surveys at 850µm (+ MAMBO at 1.2mm AzTEC, LABOCA, BOLOCAM)

Easy detection of dust FIR emission through « inverse K-correction », same flux at ~1mm from z ~ 0.5 to 10

At least ULIRGs 1012 Lo Numerous ~0.1-0.3 per arcmin2

Star Formation Rate SFR > 100 Mo/yr

Account for a significant fraction of submm background

Most exceptional HLIRGs 1013 Lo, 1000 Mo/yr nothing equivalent in the local Universe

Giant starbursts at the peak of star formation, z ~ 2-3 1-4, in massiveproto-elliptical galaxies

24µm bright z~2 ULIRGs: AGN vs PAHs/starburst

Optically faint, 24µm bright Spitzer sources high z sources

Large Spitzer surveys (SWIRE, FLS, etc.) with sensitivity S24µm~250-300µJy

(1mJy at z~2 L ~ 1012Lo)

Large programs with IRS/Spitzer spectrometer ~15-35µm ~5-12µm restHouck et al. 2005, Yan et al. 2005;2007,etc., Weedman et al. 2006, Farrah et al. 2008, Huang et al. 2008, etc.

- Most of 1mJy sources are AGN dominated: hot dust close to the BH, emitting at ~8µm

- Many have strong silicate 9.7µm absorption

-Some have strong PAH features at 6.2, 7.7, 8.6, 11.3µm, or are composite PAH/AGN

Such PAH emission is known to trace strong starbursts (PDR regions)

PAH dominated spectra Yan et al. 2007

Composite AGN-PAH spectra

Yan et al. 2007 Starburst vs AGN PAH spectrum

Composite AGN-starburst

Starbust

Stacked spectrum for10 z~1.9, Spitzer selected starburst ULIRGsHuang et al. 2008

Mid-IR properties of SMGs (for comparison)

Large range of 24µm fluxes

Average flux rather low: Pope et al. 2005 (HDFN) <S24µm> ~ 240µJy Ivison et al. 2007 (SHADES) <S24µm> ~ 340µJy

IRS spectraOnly for strongest sources: Pope et al. 2006 <S24µm> ~ 380 µJy Valiante et al. 2007 <S24µm> ~ 500 µJy

Strong PAH featuresHints of AGN

Selection of z~2 starbursts from Spitzer IRAC & 24µm photometry

IRAC bands allow discrimination between AGN and starburst (PAH) dominated sources

AGN (and many composites) have more or less power law IRAC SED

Starbursts display a ‘stellar bump’(1.6µm rest) in IRAC bands

Maximum at 5.8µm (4.5µm) bandmostly selects sources at z~1.8-2.0(1.5-1.7) Lonsdale et al. 2008, Fiolet et al. in prep.

Blue Huang08+Red Fiolet09+Green Lonsdale08+

Selection of Huang et al. 2008, from [3.6]-[4.5] vs [3.6]-[8.0], is practically equivalent to select z~2 starburst

How strong in FIR/submm are Spitzer z~2 starbursts?

Although one expects some correlation between bright sources in mid-IR(24µm at z~2), FIR and mm/submmfluxes, the detailed correlation is not obvious

Pure AGN (e.g. Type I QSOs) are known to have flat SEDs and rather weak mm fluxes

This is confirmed for obscured 24µm-bright Spitzer AGN by the1.2mm MAMBO study of Lutz et al. 2005

PAH dominated (starbursts) (andmany composite sources) havestrong/significant mm fluxes,as confirmed by our MAMBO1.2mm studies

MAMBO 1.2mm observations of Spitzer z~2 starbursts

PAH dominated (starbursts) (and many composite sources) havestrong/significant mm fluxes

Three samples

Lonsdale, Polletta, Omont et al. 2008 ApJ in press61 sources S24µm >~ 500 µJy <S24µm>=820µJy 5.8µm-peakers

16 3 detections < S1.2mm > = 1.49+/-0.18 mJy

Fiolet, Omont et al. 2009 in prep.32 sources S24µm >~ 400 µJy <S24µm>=540µJy 5.8µm-peakers

13 3 detections < S1.2mm > = 1.54+/-0.14 mJy

Younger, Omont et al. 2008, submitted to MNRAS12 sources S24µm >~ 500 µJy <S24µm>=800µJy [3.6]-[4.5] vs [3.6]-[8.0] 9 3 detections < S1.2mm > = 1.6 +/- 0.1 mJy

Homogeneous samples, no sources S1.2mm >5mJy, very few >4mJy, many 2 ‘detections’Practically all are ULIRGs/SMGs (S1.2mm = 1.5mJy S850µm ~ 4mJy)

Large ratio PAH/FIR (1.2M/24µm) emission

Ratio S(1.2mm)/S(24µm) much smaller than most SMGs whose typical SED is relatively cold, similar to Arp 220

SED rather similar to M 82 or NGC 6090But more luminous, withoutlocal equivalent (Desai 07)(or composite AGN IRAS19254)

« Optimized »sample

350µm detections

Unbiased sample

x Literature sources

Far-IR Luminosity and Star Formation Rate

Waiting for Herschel and ALMA, measuring flux densities between 40µm and 700µm is still difficult, so that the flux at SED maximum and LFIR are often uncertain

Spitzer has poor sensitivity at 70 and 160µm

Exceptionally deep 70-160µm data: Huang08+, Younger08+Tdust and LFIR well constrained by data at 70, 160 and 1200 µmTdust ~ 34 – 47 KLFIR ~ 2 – 10 x 1012 Lo

Or stack at 70-160µm of >~10 sources Lonsdale08+, Fiolet08+Similar results but more uncertain

Or/and measurement at 350µm (SHARC2/CSO) Kovacs+ in prep.The few observed sources yield similar values for Tdust and LFIR

Younger et al. 2008

Radio Properties

StarburstsLFIR (and SFR) are known to be strongly correlated with radio (synchrotron) emission in starbursts

LFIR/L1.4GHz about constant over several orders of magnitude:from HII regions to ULIRGs

Spectral index of starbursts a ~ - 0.7

AGNAGN are known to be even stronger radio emitters

Radio loud, S1.4GHz >~ 300µJy at z~2Significant radio emission from the AGN even below this limit

Various spectral index and spatial extension:Jets; flat spectrum; compact steep spectrum sources

Deep radio surveys in many Spitzer fields

Very deep radio data at 1400 and 610 MHz in a 0.25-0.5 deg2 field‘Lockman-Owen’ Field Fiolet et al. in prep.

MAMBO 1.2mm study of 32 5.8µm-peakers. High detection rate

Combination of radio + 1.2mm well discriminate AGN and starbursts

Most of our 24µm sources havea radio 30µJy detection

Ratio 1.2mm/20cm in usual limits(e.g. Chapman et al. 2005)

except 20-35% mm-faint 5 to 13 AGN?

A number are radio extended >~ 10kpc AGN or extended starbursts?

LFIR inferred from radio/FIR relationLFIR ~ 2-6 1012Lo, SFR ~ 300 –1000 Mo/yrRather consistent with Tdust ~ 40K fromYounger et al.

CO Study of 24µm bright z~2 Spitzer ULIRGs

ReminderDissecting SMGs through mm CO lines at IRAM-PdBI

Dissecting SMGs through mm CO lines at IRAM-PdBI

• (Very) Large program at the IRAM Plateau de Bure millimeter interferometer (PdBI) (Genzel, Ivison, Neri, Tacconi, Smail, Chapman, Blain, Cox, Omont, Bertoldi, Greve et al.)

• -30 SMGs with z~2-3 spectroscopic redshifts from radio positions (Chapman, et al.)

• Detection and velocity profiles of CO(3-2) and (4-3) lines for 22 SMGs (Neri et al. 2003, Greve et al. 2005, Tacconi et al. 2006, Smail et al. in prep.).

• Subarcsecond resolution imaging in progress (Tacconi et al. 2006, 2008, and in prep.)

• Parallel programs for HST imaging and high resolution radio imaging with MERLIN

• Key goals - Physical properties and evolution of the SMG population - How SMGs fit in general picture of galaxy evolution and formation

The Plateau de Bure Interferometer

In 2007 PdBI has increased sensitivity by >~2 and baseline by ~2Further gain by 2009: larger bandwidth 4GHz and more bands (2mm+0.85mm).

High angular resolution CO mapping at PdBI

Example of mapping CO in an SMG at PdBICase of an unresolved ~1kpc rotating disk

(2008)

Examples of mapping CO in SMGs at PdBISpatial and Kinematic Evidence for Mergers

Double or multiple knots, with complex, disturbed gas motions

Tacconi et al. 2008

• High CO detection rate, close to 100% with current PdBI sensitivity

• Large fraction are resolved with subarcsecond resolution (2/3 are resolved in the radio with 0.3’’ MERLIN beam)

• Mm lines of the molecular ISM, are unique to trace dynamical masses. (Also large stellar masses > 1011Mo)

• SMGs are short-duration (~100 Myr) maximum starburst events in the evolution of a major gas-rich merger of massive galaxies.

• Different combinations of ordered disk rotation and merger driven random motions and inflows

• The high surface densities in SMGs are similar to compact quiescent galaxies in the same redshift range and much higher than in local spheroids.

Current conclusions of PdBI CO survey of SMGs

CO Study of 24µm bright z~2 Spitzer ULIRGs 1/2

with upgraded PdBI(in 2007 PdBI has increased sensitivity by >~2 and baseline by ~2)

Needs accurate redshift for current PdBI limited bandwidth1 GHz for full sensitivity ( 3000 km/s)( 4 GHz in 2009)

PAH determination of z not currently accurate enough ( 2009)

Optical/NIR redshift measurement is difficult at z~1.8-2.0especially for starbursts (‘redshift desert’)

Only a dozen of IRS sources have accurate z (Sajina07+, Yan05+)

We observed 10 with PdBI and detected CO in 9

CO Study of 24µm bright z~2 Spitzer ULIRGs 2/2

We observed 10 sources of Yan+07 with PdBI and detected CO in 9Tacconi et al. in prep., Fiolet et al. in prep.

PAH dominated sources

strong CO signals; intensity and width comparable to SMGs; MH2

Most of these sources are 5.8µm-peakers or similar sources

MIPS16144 – Integrated CO 3-2 Emission

‘PAH’ source, Mambo flux=2.930.56, z=2.1340 MHz spectral smoothing, rms=0.32 mJy/beamC-configuration

strong PAHs

strong MAMBO 1.2m flux (2.9mJy)

strong CO

L. Tacconi in prep.

CO Study of 24µm bright z~2 Spitzer ULIRGs 2/2

We observed 10 sources of Yan+07 with PdBI and detected CO in 9Tacconi et al. in prep., Fiolet et al. in prep.

PAH dominated sources strong CO signals; intensity and width comparable to SMGs; MH2

AGN dominated and composite sources

weaker (narrower) CO lines but most are detected

CO is detectable with current PdBI sensitivity in practically all z~2 ULIRGs

High resolution maps in one sources in Winter 2009? Multi-line CO observations in 2mm (1.3mm) bands?? Search in large sample with PAH redshift with 4 GHz bandwidth??

MIPS15949 – Integrated CO 3-2 Emission

AGN (+PAH) source, Mambo flux=1.240.51, z=2.1140 MHz spectral smoothing, rms=0.28 mJy/beamC-configurationCO43=148 CO65=222

PdBI Spring08 ROC4

MIPS8327 – Integrated CO 3-2 Emission

Absorbed source, Mambo flux=1.030.55, z=2.4440 Mhz spectral smoothing, rms=0.24 mJy/beamC-configurationCO54=167.52

PdBI Spring08 ROC4

MIPS8342 – Integrated CO 2-1 Emission

AGN (+‘PAH’) source, Mambo flux=0.980.55, z=1.5640 MHz spectral smoothing, rms=0.19 mJy/beamNote: this source was done in D-configurationCO32=

PdBI Spring08 ROC4

Srong 10µm silicate absorption

Narrow CO line, radio loud

Fiolet et al. in prep.

Weak 1.2mm MAMBO

Broad CO line

Spatial Extension

Crucial: a significant extension could explain stronger PAHs (merger, outflow?)While most SMGs and AGN are rather compact (+strong silicate absorption)But difficult, subarcsec

Best: CO (+1.2mm continuum) maps at PdBI of strong sourcesALMA for weak sources

HST ACS (Huang+08), NICMOS (Dasyra,Yan+08) : many sources extendedbut difficult interpretation

Radio: many large extensions (Owen; Fiolet in prep.)but could be AGN jets or merger starbursts

Stellar Masses

Stellar mass well traced by NIR emission (1.6µm bump) of red giantsIRAC bands at z~2

But risk of contamination by young massive TP-AGBs

Large mass (>~1011Mo) (Berta+07 Lonsdale+08, Fiolet+08, Huang-Younger 08)

Maybe slightly larger than SMGs?

Conclusions. Comparaison with classical SMGs

PAH luminous z~2 sources are strong starbursts and belong to the SMG family special subclass, probably extended starburst (from late major mergers)

Compared to the bulk of the SMGs, they have:

• Comparable mm/submm fluxes and CO intensities

• Significantly larger 24µm/1.2mm flux ratio

• Probably slightly larger Tdust (mean ~40K instead ~34K)

Herschel Too small collecting area vs ALMA (/500!) for high-z molecules

But will detect 104’s of SMGs in wide surveys with full SEDs, LFIR and SFR

For follow up at PdBI and ALMA

Will need multi- data to beat confusion

SPIRE GTO high-z ‘HERMES’: 900h mapping most Spitzer survey fields

GO key project ATLAS: ~500h, ~500 deg2 shallow observations : nearby and rare (lensed) objects

GO key project 300h on ~50 lensing clusters

Prospects

Herschel bands and SMG SEDs

JWSTMIRI/JWST will have orders of magnitude improvements in sensitivity, spatial and/or spectral resolution compared with Spitzer

synergy with ALMA

Prospects

ALMA

ALMA will provide exquisite CO images, and multi-line intensitiesfor such galaxies and more distant ones