Anton Koekemoer Space Telescope Science Institute Anton Koekemoer

Anton Koekemoer (Space Telescope Science Institute) Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 Probing AGN Populations at Redshifts 6 - 7+ with Large X-ray Surveys 1 + CDFS/GOODS-AGN (Alexander, Brandt, Bergeron, Conselice, Chary, Cristiani, Daddi, Dickinson, Elbaz, Grogin, Mainieri, Treister, Urry, . . . ) +COSMOS-AGN (Brusa, Carilli, Comastri, Elvis, Fiore, Gilli, Hasinger, Salvato, Sasaki, Scoville, Schinnerer, Taniguchi, Trump, Zamorani, . . . )

Black holes in the context of reionization: May trace hierarchical dark matter halos l Provide harder ionizing continuum than stars l May regulate galaxy growth / SFR via feedback l M-s relation suggests intimate connection between BH/galaxy formation and growth Current knowledge: At z ~ 6 - 6. 5, already have supermassive BHs up to M ~ 3 x 109 Mo (Fan et al 2001+; Willott et al. 2003) l High-luminosity end of AGN LF evolves strongly from z~6 to z~2; PLE is ruled out (Fan et al. 2001+; Richards et al. 2006) l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 2

Instead of PLE, AGN appear to follow “downsizing” -luminosity-dependent density evolution “LDDE” -- for X -ray LF (Ueda et al. 2003, Hasinger et al. 2005) and also for QSO LF (Richards et al. 2006): – luminous AGN peak earlier (z~2 -3) – fainter AGN peak more recently (z~1) (XLF; Hasinger et al. 2005) Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 3 (QSO LF, Richards et al. 2006)

Questions: How do the most massive BHs form within < 1 Gyr? l How does BH growth influence the M-s relation? l What is the ionizing budget of AGN integrated over the LF beyond z ~ 6, and its contribution to reionization? l (How) does obscured/unobsc. AGN ratio evolve at z > 6? Our knowledge has been limited by the following: only the top of the AGN LF has been studied at z ~ 6 l no AGN currently confirmed at z > 7 l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 4 Approach: Set out to quantify the faint end of AGN LF at z ~ 6 l Search for more luminous AGN at z > 6 - 7 l

Require Wide+Deep X-ray / Optical / IR Surveys: Depth probes faint/moderate-lum AGN to high z l Area probes high-lum AGN at high z l (Hard) X-rays penetrate obscuring torus, IR probes restframe optical emission from AGN + host galaxy New part of parameter space: 5 Combined optical + X-ray depth allows wider exploration of FX/FOpt: log FX (erg s-1 cm-2) Anton Koekemoer (STSc. I) l N AG Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l FOpt (mag)

CDFS/GOODS-S+N survey: powerful combination of wide area and depth, opt/Xray: CDFS + CDFN have 1 & 2 Msec Chandra depth respectively l X-ray depth sufficient for AGN LF faint end (L X~1043 -44 erg s 1) up to z ≥ 6 - 7 l area sufficient (0. 1 sq deg) to provide number statistics on AGN LF at these redshifts l More than 800 AGN from Chandra in GOODS-N & S (> 600 covered by HST/ACS and Spitzer) l Extensive optical spectroscopic coverage l deep multi-band optical/NIR coverage Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l l Spitzer/IRAC 3. 6 – 8 mm observations trace host stellar mass for z > 1 -2 Spitzer/MIPS 24 mm data helps constrain thermal dust emission

X-ray data: l CDFS (Giacconi, Hasinger et al. 2001+): – 940 ksec divided over 11 intervals, one orientation CDFN (Brandt et al. 2001+): – 2 Msec, on original Hubble Deep Field (HDFN) CDFS Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 7 CDFN

Selection criteria: t= op 1 10 0. Expect mostly obscured sources, but unobscured AGN are not excluded Highest FX/FOpt: 8 u uu uu found in several studies so far (Koekemoer et al 2002; Tozzi et al 2002; Brusa et al. 2004; Koekemoer et al 2004, 2006) l EXO’s - Extreme X-ray / Optical sources l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 /F FX t= l op – Drop-outs in z 850 lp (>27) – Anomalous Fx/Fopt (>100) – Red z 850 lp - K (>4) /F Based on SED change with z: FX l CDFS (Brandt et al, Koekemoer et al, 2001 - 2005) – – Only revealed by extending optical depth below ~27 Optically faint sources with anomalously high FX/FOpt >100 Typically have extremely red z-K > 4 -6 Appear to have no comparable analogs in the local universe

Candidate high-z AGN: X-ray properties: Well-detected by Chandra (~10 -16 -10 -15 erg s-1 cm-2) l FX/FOpt is a lower limit, and is > ~100 x above the average for AGN l Similar number in CDFN l Generally have soft and hard X-ray emission (excludes z<2 obscured AGN) Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 9 Redder z-K colour: most AGN with FX/FOpt ~ 0. 1 - 10 have fairly tight z-K ~1 -2, with some slight scatter: – z-K ~ -1 to 2 for quasars/Seyferts – z-K ~ 2 to 4 for ERO’s l However, the EXO high-z candidates generally have z-K >4 l

Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 EXO high-z candidates from GOODS HST/ACS 10 VLT+NOAO SPITZER/IRAC MIPS

Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 EXO Close-up (contours = Chandra 0. 5 -8 ke. V) 11

SEDs: NIR+Spitzer Colours: Optical-NIR: red l NIR-IRAC: red l within IRAC: – generally red – some flat/blue Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 12 HST/ACS BViz limits • 28

High-z Candidate SED Constraints Two fundamental observational constraints: NIR/IRAC colours - generally red for EXO’s: – typically K - IRAC 1 (or IRAC 2) ~ 2 mag(AB) – some of the sources have K - IRAC ~ 3 mag l IRAC colours: – Some have red IRAC 1 -IRAC 3 (or IRAC 2 -IRAC 4) – Others have flat or blue IRAC colours Goal of SED fitting: l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 13 Explore a full grid of parameters to differentiate high-z from lower-z (eg z~2 -3 “red and dead” DRGs, etc): – use Charlot & Bruzual (2003), also Maraston (2005 -2006) – combine SSP + CSP – reddening laws (Calzetti, LMC, SMC, galactic) l Several sources may have 2 redshift peaks (z~2 -3, or a high -z alternative); consider both possibilities in that case

SED Fitting Parameterization: l l l h - stellar mass formed as SSP / CSP t - reddening (Fall & Charlot; Calzetti; SMC; LMC) Fits driven by two observational features: red opt/NIR - IRAC colours l colours within IRAC l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l redshift Mass 14 General results: a number of the z 850 lp>27 sources are indeed fit by z~2 -3 old populations with little or no dust l younger models requiring more dust l host galaxies typically underluminous (c. f. AGN locally) l

some examples (from GOODS): some EXOs are fit by z~2 -3 evolved or dusty SEDs l others have higher-z fits l host galaxies typically underluminous (c. f. AGN locally) l Mainieri et al 2005 (JHK), Koekemoer et al 2006 (Spitzer) Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 15

Old populations with little/no reddening: l l l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 16 z ~ 2. 5 - 5 t~0 -1 h~0 M ~ 109 - 1010 Mo

Younger populations requiring more reddening: l l l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 17 z~2 -4 t~5 h~0 M ~ 109. 3 - 109. 7 Mo

Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 Candidate z>7 AGN: 18

Constraining high-z AGN LF: Use Ueda / Hasinger / Gilli hard X-ray XLF to estimate expected number of optically unidentified sources as a function of redshift l Most of the optically unidentified AGN are evolved interlopers at intermediate z > 2 l Compare with observed number of undetected sources: – use existing X-ray detection limits – apply optical detection cut-off (z(AB) ~ 27. 5 for ACS) Integrate over X-ray luminosities at each redshift bin l Use the difference to calculate cumulative number N(>6) l Compare with N(>6) from XLF l Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 19

Constraints on z~7 AGN LF: at z~7, sensitive to Lx ~ 1044 erg s-1 cm-2 l Expected ~3 sources, found 1 candidate so far l other sources are ruled out as lower-z interlopers l Convert this to a limit on the LDDE XLF: z~7 Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 20 Thus, possible slight change in low end of AGN LF at z>7 l Supports continued “downsizing”, ie fewer low-lum AGN, thus fewer minor accretion events compared with major mergers or high-luminosity AGN fuelling l

Next: Expand the EXO sample - COSMOS Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 21 600 orbits of HST/ACS, i-band, 27 th mag

COSMOS HST/ACS: 2 million galaxies, ~1300 AGN (XMM: Hasinger et al, Brusa et al 2006) + radio (Schinnerer et al) ~1. 4° Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 22

Conclusions: Overall number of AGN found in GOODS agrees with that expected based on LDDE l Intermediate-z interlopers successfully accounted for l Found at least 1 plausible candidate z > 7 AGN in GOODS; compared with 3 expected from extending LDDE to z ~ 7 l Thus LDDE appears to extend up to at least z ~ 7 (although possible additional decr in faint end of AGN LF) l Suggests that AGN growth/accretion mechanisms continue to track galaxy growth into reionization: Anton Koekemoer (STSc. I) Extragalactic X-Ray Surveys - Cambridge, MA, 6 Nov 2006 l 23 – AGN feedback regulating star formation up to early epochs – black holes tracing dark matter halos since at least z ~ 7 l Next steps: – larger/deeper multi-band area coverage is needed to improve the sample statistics – deep red optical + IR spectroscopy is also needed!