Star Formation in High Redshift Submillimeter Galaxies and QSO Hosts

Dieter LutzMPE

Elisabetta Valiante, Eckhard Sturm, Reinhard Genzel, Linda Tacconi, Mario Schweitzer, Andrew Baker, Hagai Netzer, Roberto Maiolino, Paola Andreani, Sylvain Veilleux

Gas Accretion and Star Formation in Galaxies, September 14, 2007

Starburst/AGN co-evolution…

Hopkins et al. 2006GOODS-S

Hughes et al. 1998

This talk:

Use rest frame mid-infrared spectroscopy to quantify current star formation and AGN activity in high z populations

Spitzer QUEST Veilleux et al.

SMGs - a key phase of massive galaxy evolution

Smail et al. 2002 Genzel et al. 2003, Greve et al. 2005 Swinbank et al. 2006

Spitzer-IRS: Redshifts Energy Sources Constraints on source structure (from SED)

Sample

• 13 bright objects from blank field or lens assisted SCUBA 850m and MAMBO 1.2mm surveys – no radio pre-selection• GO1 selection, not including Spitzer fluxes

• Accurate positions from radio or mm interferometry

• Wide range of optical/near-infrared counterpart brightnesses• 6/13 with known optical redshifts

• Up to 2 hours per IRS low resolution order, to reach sub-mJy sensitivity

Bertoldi et al. 2000Smail et al. 2002Ivison et al. 2002Cowie, Barger & Kneib 2002Dannerbauer et al. 2002

Frayer et al. 2000

IRS spectra

Lutz et al. 2005 ApJL 625, L83Valiante et al. 2007 ApJ 660,1060

z~2.8

IRS redshifts of SMGs

Can be obtained at S24m <1mJy!

• 6 optical redshifts confirmed, within z~0.02

• 3 new PAH redshifts: 2.38, 2.73, 2.79

• 4 sources remain without redshift – z>3.6?

Median z~2.8 - support for an SMG median redshift modestly higher than the Chapman 05 value of 2.2 from optical spectroscopy

Chapman et al. 2005

SMGs: Starburst and AGN

Average SMG spectrum at z~2.7(Valiante et al. 2007)

Strong PAH emission: Luminosity star-formation dominated

Additional AGN continuum:AGN typically 10-20% of luminosity, X-ray must be noticeably obscured

…consistent with and extending to Compton-thick objects the X-ray based work of Alexander et al.

See also Menendez-Delmestre et al. 2007 (slightly different selection of SMGs)

ULIRG-like SEDs - consistent with compact (few kpc) sizes

Bouche et al. 2007 arXiv:0706.2656

Tacconi et al. 2006 ApJ8 SMGs median d(CO)<4kpc

Evidence for star formation in high z QSOs?

Omont et al. 2003

Walter et al. 2003,Maiolino et al. 2005

Elvis et al. 1994

Local studies: What is the origin of QSO rest frame FIR emission?

Rowan-Robinson (1995): Radiative transfer model of pure AGN SED Strong far-infrared (if observed) must be star formation

Optical post-starburst signatures: e.g. Canalizo & Stockton 01, Kauffmann et al. 03

Sanders et al. 1989: warped disk couldprovide enough cold but AGN-heated dust

Ho 2005: [OII] 3727 study- Little star formation, inhibited by QSO?

Average local PG QSO spectra: PAH emissions is widespread

Schweitzer et al. 2006

Star formation tracers and QSO far-infrared emission correlate

PAH/FIR and [NeII]/FIR Ratios in QSOs = Ratios in starbursting ULIRGs

Star formation!

Reconstructing the intrinsic AGN SED

Netzer et al. 2007 ApJ 666, 806 0.15~LFir/LBol = LSB/LBol

→ Currently: Bulge growth rate ~ 20*BH growth rate *(η/0.1)Lifetime/Duty cycle of bright QSO short, or shifted

3μm bump Silicates

Using PAHs to quantify star formation in ‘Quasar epoch’ QSOs

Spitzer-IRS studies:• 12 QSOs 1.8<z<2.8 with robust submm/mm detections (e.g. Omont et

al. 03, Priddey et al. 03, Barvainis & Ivison 02)– mm-bright end of the z~2.5 QSO population, but not extreme IR excess

objects

– Long integrations to individually measure PAH emission

Cycle 3, Lutz et al. 2007 ApJ 661, L25 and in preparation

• 25 QSOs 2<z<3.5 without mm preselection– Short integrations insufficient for individual PAH study, but meaningful

stack

Cycle 2, Maiolino et al. 2007 A&A 468, 979

PAH detection in the z=2.56 Cloverleaf lensed QSO

Lutz et al. 2007, ApJ 661, L25

Kneib et al. 1998

LAGN ~ 7 1013LSun

LSB ~ 5 1012LSun → SFR ~1000 MSun/yrGas exhaustion time 3 107yr

Star formation: PAH emission is consistent with rest frame FIR

Star formation: PAH emission is consistent with rest frame FIR

Extrapolation to other luminous high-z QSOs

Maiolino et al. 2007 A&A 468, 979

PAH limit for average of 25 luminous 2<z<3.5 QSOs NOT preselected in the mm→ SFR < 700 Msun/yr

Schweitzer et al.PG QSOs

Cloverleaf

• PAH detection strongly supports ~1000Msun/yr star formation rates in mm-detected high-z QSOs• These have similar ratio of PAH (and FIR) to the AGN luminosity as local PG QSOs

• Bulk of z~2.5 QSO population has somewhat lower ratios of mm to AGN luminosity, typical SFRs will not exceed a few hundred Msun/yr• Local relation between star formation and AGN luminosity must flatten at high L/high z)

Summary

• IRS spectroscopy of a small sample of SMGs suggests them to be z~2.8, dominated by luminous compact starbursts but with frequent coexisting minor AGN (sometimes Compton-thick).

• IRS spectroscopy detects strong star formation in the hosts of local PG QSOs, and massive ~1000Msun/yr star forming events in submm-bright high z QSOs. Stars are sufficient for producing their rest frame FIR emission. The typical z~2.5 luminous QSOs has less intense star formation, and a lower ratio of star formation to AGN luminosity.