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EXOs: Candidate AGN at z ≥ 6 and intermediate-z evolved populations

EXOs: Candidate AGN at z ≥ 6 and intermediate-z evolved populations. Anton Koekemoer (Space Telescope Science Institute) + GOODS (Alexander, Bauer, Brandt, Chary, Conselice, Cristiani, Daddi, Dickinson, Elbaz, Grogin, Mainieri, Tozzi,..)

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EXOs: Candidate AGN at z ≥ 6 and intermediate-z evolved populations

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  1. Galaxies and Structures through Cosmic Times, Venice • EXOs: Candidate AGN at z ≥ 6 • and intermediate-z evolved populations Anton Koekemoer (Space Telescope Science Institute) + GOODS (Alexander, Bauer, Brandt, Chary, Conselice, Cristiani, Daddi, Dickinson, Elbaz, Grogin, Mainieri, Tozzi,..) + COSMOS-XMM (Brusa, Comastri, Elvis, Finoguenov, Fiore, Gilli, Hasinger, Impey, Mainieri, Salvato, ..)

  2. Galaxies and Structures through Cosmic Times, Venice AGN log FX (erg s-1cm-2) FOpt (mag) • Large X-ray/optical/IR surveys are opening up new regions of parameter space: • Depth probes faint end of AGN LF to high z • Area probes high end of AGN LF at high z • Combined optical + X-ray depth allows wider exploration of FX/FOpt and new populations • Relevant surveys: • GOODS/CDFN+S (15’) • E-CDFS (30’) • XMM-LH (30’) • EGS (10’x 60’) • COSMOS (1.4o x 1.4o) • ..

  3. Galaxies and Structures through Cosmic Times, Venice FX/Fopt = 0.1 FX/Fopt = 10 u u u u u u u • FX/FOpt parameter space: • AGN typically ~1-2 dex • SB are lower Fx/Fopt • Highest FX/FOpt: • “EXO’s” - Extreme X-ray /Optical sources: • Fx/Fopt > ~100 • Only revealed byextending optical depthbelow i or z ~ 24 - 25 • Appear to have no comparable analogs in the local universe • Why do we only start seeing them at faint magnitudes? • What produces the high FX/FOpt - these sources likely consist of two sub-populations: • Balmer break: z ~ 2 - 3 evolved or dusty hosts (DRGs, EROs) • Lyman break: candidate z > 6-7 agn

  4. Galaxies and Structures through Cosmic Times, Venice • Fx/Fopt vs Colour: • Sources with low FX/FOptare generally blue: low-zstar-forming galaxies • Some blue sources alsohave FX/FOpt typical ofunobscured AGN- quasars • Moderately red galaxies(z - K > 2) all have higherFX/FOpt, obscured AGN • Reddest z - K sources: • for z - K > 4, FX/FOpt increases to ~ 10 - 100x the value for even typical obscured AGN • Not a selection effect: • high FX/FOpt should not necessarily imply bright IR flux • Thus red opt/IR colour is intrinsic characteristic of EXOs

  5. Galaxies and Structures through Cosmic Times, Venice • Previous studies of optically faint X-ray sources: • Initial Deep Chandra/XMM fields revealed that ~20-30% ofX-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 FX/FOpt typical of obscured AGN at z ~ 1-3 (Brusa et al. 2003, Mainieri et al. 2004, Fiore et al 2005) • Some optically faint sources are ERO’s (z ~ 1-1.5) - but also have normal FX/FOpt(Stevens et al. 2003, Yan et al. 2003, Rigby et al. 2005) • EXO’s: • Optically faint sources with anomalously high FX/FOpt >100 • No apparent local analogs at brighter magnitudes • Typically have redder z-K than ERO’s (Koekemoer et al. 2004, 2006)

  6. Galaxies and Structures through Cosmic Times, Venice • Nature of EXOs: • Need further IR constraints on SED to determine which sub-population a given EXO belongs to based on its red opt/IR: • Balmer break (z ~ 2 - 3 evolved or dusty populations) • Lyman break (z >6 AGN) • NOTE: expect EXOs to contain both z~2-3 and z>6 sources • Spitzer data: • currently based purely on GOODS CDFS + HDFN (Dickinson) • all EXOs are detected in IRAC data: • red K - IRAC colour • across IRAC, have a mixture of SEDs (red, flat or blue) • MIPS detections/non-detections are consistent with IRAC properties: • flat/red IRAC -> MIPS detections, usually brighter than IRAC • blue IRAC colours -> generally undetected in MIPS

  7. Galaxies and Structures through Cosmic Times, Venice HST/ACSSPITZER/IRAC MIPS HST/ACSVLT/ISAACSPITZER/IRAC

  8. Galaxies and Structures through Cosmic Times, Venice

  9. Galaxies and Structures through Cosmic Times, Venice • SED fitting: • Parameters SSP + constant SFR, reddening, IMF, dust • Models: • initally used CB2003 • will also now include Maraston • Results: • Most EXOs arewell fit by: • z ~ 2 - 3 • evolved • ~1010-11 Mo • Some requirereddening AV ~1 • A few EXOs arenot well fit byz ~ 2 - 3 models

  10. Galaxies and Structures through Cosmic Times, Venice • Using EXOs to trace high-z AGN evolution: • AGN regulate galaxy growth / SFR via feedback • may trace hierarchical dark matter halos • possibly different types of accretion mechanisms: • luminous AGN may trace major mergers • lower-luminosity AGN may trace more minor interactions and accretion events (e.g.Merloni et al. 2004) • Hasinger etal. luminosity-dependent density evolution LDDE: • High-lum AGN grow earlier in universe, peak at z ~ 2 • Lower-lum AGN peak much later, z~1, decline by 10x to z=0 • Questions: • how does the faint end of the AGN LF evolve beyond z ~6? • does obscured/unobscured AGN ratio increase beyond z ~6? • does more rapid evolution of high-lum AGN trace merging history of spheroid formation?(e.g, Franceschini et al 1999)

  11. Galaxies and Structures through Cosmic Times, Venice • Using EXOs to count high-z AGN in GOODS: • Use XLF to estimate expected number of optically unidentified sources as a function of redshift • Most of the optically unidentified AGN are evolved interlopers at intermediate z > 2 • 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 • 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. Galaxies and Structures through Cosmic Times, Venice • Predict optically unidentified sources in each redshift bin using Hasinger et al. LDDE description, extrapolating upto z ~ 7 • Apply to GOODS X-rayselection, including theoptical detection limits, tocalculate EXOs expected. • Number of optically unID’d sources N(z) based onz(AB)=27.5 limit, for currentChandra catalogs: • LDDE predicts 9 - 16 EXOs in GOODS (out of 607 X-ray sources): • 8-13 should be at z ~ 2 - 5 • 1-3 should be at z ~ 6 - 7 • Actually detect 13 EXOs: • SED modelling confirmsthat 10 are at z ~ 2 - 4 • 3 are indeterminate

  13. Galaxies and Structures through Cosmic Times, Venice • Conclusions: • Number of EXO’s found in GOODS agrees well with that expected based on LDDE (13 vs 9-16, respectively) • Number of intermediate-z interlopers among EXOs also agrees with expected from LDDE (10/13 vs 8-13/9-16) • Remaining number of 3 EXOs in GOODS with possible high redshifts (ie > 6) is consistent with the 1-3 EXOs expected at z > 6 based on extending LDDE to z ~ 6 – 7 • Therefore LDDE appears to extend up to at least z ~ 6 - 7 • This suggests that AGN growth/accretion mechanisms continue to track galaxy growth into reionization: • AGN feedback regulating star formation up to early epochs • black holes tracing dark matter halos since at least z ~ 7 • Future: • extend to COSMOS to improve LF constraints (whenever Spitzer catalogs are available for SED fitting..)

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