1. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 1 Using COSMOS to Probe the High-Redshift AGN Population Anton Koekemoer (Space Telescope Science Institute) + COSMOS XMM / AGN Team: M. Brusa, A. Comastri, N. Cappelluti, F. Civano, M. Elvis, A. Finoguenov, F. Fiore, R. Gilli, G. Hasinger, C. Impey, V. Mainieri, M. Salvato, C. M. Urry, C. Vignali, G. Zamorani

2. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 2 Supermassive BH’s - questions: How & when do they form? How do they grow & evolve? What is their impact on galaxy growth (eg feedback) What sets SBH mass  host bulge mass ? Context: Already have SBH ~ 10 9 M o at z~6 (Fan et al. 02, 03, 05) Quasar LF changes with redshift: –simple luminosity evolution (PLE) is ruled out –instead, seem to have density evolution at high end of the LF (Fan et al 2003)

3. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 3 However: LF density evolution is not the same for all luminosities LF shape changes with redshift: Lum.-depdendent density evolution (Hasinger et al 2005) Higher-lum objects: –grow early in universe –peak at z ~ 2 –decline by 100x from z ~ 2 to present Lower-lum objects: –growth peaks much later, z ~ 1 –decline only by <10x from z ~ 1 to present

4. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 4 (from Hasinger et al. 2005)

5. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 5 Below L X ~ 10 44 erg s -1, density evolution is drastically different from higher-lum sources, peaking at lower z higher-lum sources show essentially pure density evolution suggests possible difference in accretion / galaxy evolution as a function of luminosity (Hasinger et al. 2005)

6. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 6 Physical picture to date: rapid evolution of high-lum AGN appears to trace merging history of spheroid formation (e.g, Franceschini et al 1999) much later peak and slower decline of lower-lum AGN more closely resembles star formation history which peaks later at z ~ 1 thus potentially two different modes of accretion and black hole growth with radically different accretion efficiency (eg Merloni et al. 2004) - corresponds essentially to galaxy mergers vs interactions Next steps: need to extend picture for z < 2 - 4 to higher-z & low-lum: –do these modes of BH growth / accretion apply at < 1 Gyr? –what is the role of AGN feedback in early universe in determining the eventual bulge / BH mass relation?

7. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 7 How can COSMOS help? unique combination of wide area and depth, opt/Xray 2 sq deg large enough to probe rare high end of AGN LF at L X > 10 45 - 46 erg s -1 X-ray coverage deep enough to probe fainter end of AGN LF (L X ~ 10 44 erg s -1 ) up to z ~ 6 - 7 At least ~ 1000 AGN from XMM (654 to date; Brusa et al) Extensive optical spectroscopic coverage deep multi-band optical/NIR coverage Spitzer IRAC observations will trace host stellar mass for z > 1-2; MIPS will help constrain thermal dust emision

8. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 8 XMM Observations: Initial dataset covers 12 pointings (Brusa et al) Area covered ~1.3 sq deg Total of 715 X-ray sources detected; ~20 extended Limiting fluxes: –F(0.5-2 keV) ~ 1 x 10 -15 erg cm -2 s -1 –F(2-10 keV) ~ 5 x 10 -15 erg cm -2 s -1 Final survey: total of 23 fields, covering 2 sq deg aim for ~1500 X-ray sources

9. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 9 Searching for High-z AGN First, ensure most X-ray sources have ID, z: ~80% identified (Brusa et al.) spectroscopy as complete as possible (Impey, Trump et al.) Next, examine ambiguous IDs: mostly expected from limited XMM spatial resolution corresponds to multiple optical IDs inside formal positional error circles Finally, produce sample of EXOs: some of these are red/evolved obscured AGN at z ~ 2 - 5 remaining fraction are candidates for z > 6 AGN Really need combined optical/NIR/Spitzer to help disentangle these possibilities, for any given source

10. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 10 EXOs to date: Previous studies of optically faint X-ray sources: Initial Deep Chandra/XMM fields revealed that ~20-30% of X-ray sources are “optically faint”, R > 24 (Koekemoer et al. 2002, Tozzi et al. 2002) Most optically faint sources are also X-ray faint, ie have fairly normal F X /F Opt typical of obscured AGN at z ~ 1-3 (Brusa et al. 2003, Mainieri et al. 2004) Some optically faint sources are ERO’s (z ~ 1-1.5) - but also have normal F X /F Opt (Stevens et al. 2003, Yan et al. 2003) EXO’s: Optically faint sources with anomalously high F X /F Opt >100 Typically have much redder z-K colour than even the ERO’s (Koekemoer et al. 2004) SED models: single-burst / continuou SFR + dust reddening (see also Mainieri et al 2005)

11. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 11 Using EXOs to count High-z AGN in COSMOS: Use XLF to estimate expected number of optically unidentified sources as a function of redshift expect some X-ray AGN to be optically undetected starting at z > 2 Compare with observed number of undetected sources: –use existing X-ray detection limits –apply optical detection cut-off (I(AB) ~ 26 for Subaru, I(AB) ~ 27 for ACS) Integrate over X-ray luminosities at each redshift bin assume Type 1/2 ratio found in GOODS by Treister et al Use the difference to calculate cumulative number N(>6) Compare with N(>6) from XLF

12. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 12 predict optically unidentified sources in each bin using Hasinger et al. LDDE description apply to COSMOS X-ray selection, including the optical detection limits Number of optically unID’d sources N(z) based on I(AB)=26 limit, for current (12-pointing) XMM catalog LDDE predicts ~70 EXO’s Compare with ~40 sources (Brusa et al)

13. Anton Koekemoer AAS 207, Washington DC, 10 January 2006 13 Summary Preliminary results: Based on luminosity-dependent density evolution, expect a total of ~10% optically unidentified sources to AB~26 in the current XMM catalog, with ~2% expected at z~6 current total of unidentified sources (Brusa et al) is ~5% Once lower-z EXOs are accounted for, this suggests ~ 2x less AGN than expected at z~5-6 Marginally inconsistent with extension of LDDE to z~6 suggests AGN accretion / growth mechanisms at z~6 may be starting to differ from those seen at z < 2 - 4, eg more dominated by extreme accretion events Future: Spectroscopy (Impey, Trump); Spitzer imaging (Sanders) SED modelling to better constrain redshifts