Star Formation in High Redshift Submillimeter Galaxies and QSO Hosts

1. Star Formation in High Redshift Submillimeter Galaxies and QSO Hosts Dieter Lutz MPE 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

2. Starburst/AGN co-evolution… Hughes et al. 1998 GOODS-S Hopkins et al. 2006

3. 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.

4. 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)

5. Sample • 13 bright objects from blank field or lens assisted SCUBA 850m 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. 2000 • Smail et al. 2002 • Ivison et al. 2002 • Cowie, Barger & Kneib 2002 • Dannerbauer et al. 2002 Frayer et al. 2000

6. IRS spectra z~2.8 Lutz et al. 2005 ApJL 625, L83 Valiante et al. 2007 ApJ 660,1060

7. Chapman et al. 2005 IRS redshifts of SMGs • Can be obtained at S24m <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

8. 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. SMGs: Starburst and AGN Average SMG spectrum at z~2.7 (Valiante et al. 2007) See also Menendez-Delmestre et al. 2007 (slightly different selection of SMGs)

9. ULIRG-like SEDs - consistent with compact (few kpc) sizes Bouche et al. 2007 arXiv:0706.2656 Tacconi et al. 2006 ApJ 8 SMGs median d(CO)<4kpc

10. Evidence for star formation in high z QSOs? Omont et al. 2003 Walter et al. 2003, Maiolino et al. 2005

11. Elvis et al. 1994 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 could provide enough cold but AGN-heated dust Ho 2005: [OII] 3727 study - Little star formation, inhibited by QSO? Local studies: What is the origin of QSO rest frame FIR emission?

12. Average local PG QSO spectra: PAH emissions is widespread Schweitzer et al. 2006

13. Star formation tracers and QSO far-infrared emission correlate PAH/FIR and [NeII]/FIR Ratios in QSOs = Ratios in starbursting ULIRGs Star formation!

14. Reconstructing the intrinsic AGN SED 3μm bump Silicates 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

15. 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

16. PAH detection in the z=2.56 Cloverleaf lensed QSO Lutz et al. 2007, ApJ 661, L25 LAGN ~ 7 1013LSun LSB ~ 5 1012LSun→ SFR ~1000 MSun/yr Gas exhaustion time 3 107yr Kneib et al. 1998

17. Star formation: PAH emission is consistent with rest frame FIR

18. Star formation: PAH emission is consistent with rest frame FIR

19. Cloverleaf Extrapolation to other luminous high-z QSOs • 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) Schweitzer et al. PG 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

20. 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.