AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

Using COSMOS to Probe theHigh-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

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

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 ~ 109 Mo

at z~6 (Fan et al. 02, 03, 05)Quasar LF changes with redshift:

– simple luminosity evolution(PLE) is ruled out

– instead, seem to havedensity evolution at highend of the LF

(Fan et al 2003)

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

However:LF density evolution is not the same for all

luminositiesLF 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

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

(from Hasinger et al. 2005)

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Anton Koekemoer

Below LX ~ 1044 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)

-15

-13

-11

-9

-7

-5

-3

41.5 42.5 43.5 44.5 45.5 46.5 47.5

Log Lx (erg/s)

z = 0.015 - 0.2

z = 0.2 - 0.4

z = 0.4 - 0.8

z = 0.8 - 1.6

z = 1.6 - 3.2

z = 3.2 - 4.8 -15

-13

-11

-9

-7

-5

-3

0.1 0.6 2.4

redshift

d(p

hi)

/d(l

og

L)

(Mp

c-3)

Lx = 42.0

Lx = 43.0

Lx = 44.0

Lx = 45.0

Lx = 46.0

Lx = 47.0

Lx = 48.0

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

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?

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

How can COSMOS help?unique combination of wide area and depth,

opt/Xray2 sq deg large enough to probe rare high end of

AGN LF at LX > 1045 - 46 erg s-1

X-ray coverage deep enough to probe fainter end of AGN LF (LX ~ 1044 erg s-1) up to z ~ 6 - 7

At least ~ 1000 AGN from XMM (654 to date; Brusa et al)

Extensive optical spectroscopic coveragedeep multi-band optical/NIR coverageSpitzer IRAC observations will trace host stellar mass

forz > 1-2; MIPS will help constrain thermal dust emision

AAS 207, Washington DC, 10 January 2006

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Anton Koekemoer

XMM Observations: Initial dataset covers 12 pointings (Brusa et al)Area covered ~1.3 sq degTotal of 715 X-ray sources detected; ~20 extendedLimiting 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 degaim for ~1500 X-ray sources

AAS 207, Washington DC, 10 January 2006

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Anton KoekemoerSearching 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 resolutioncorresponds 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 AGNReally need combined optical/NIR/Spitzer to help

disentangle these possibilities, for any given source

AAS 207, Washington DC, 10 January 2006

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Anton KoekemoerEXOs 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 FX/FOpt 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 FX/FOpt (Stevens et al. 2003, Yan et al. 2003)

EXO’s:Optically faint sources with anomalously high FX/FOpt >100Typically 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)

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Anton Koekemoer

Using EXOs to count High-z AGN in COSMOS:Use XLF to estimate expected number of optically

unidentified sources as a function of redshiftexpect some X-ray AGN to be optically undetected

starting at z > 2Compare 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 binassume Type 1/2 ratio found in GOODS by Treister et alUse the difference to calculate cumulative number

N(>6)Compare with N(>6) from XLF

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Anton Koekemoer

predict optically unidentified sources in each bin using Hasinger et al. LDDE description

apply to COSMOS X-rayselection, including theoptical detection limits

Number of optically unID’d sources N(z) based onI(AB)=26 limit, for current(12-pointing) XMM catalog

LDDE predicts ~70 EXO’sCompare with ~40 sources

(Brusa et al)

02468

101214161820

0 - 1 1 - 2 2 - 3 3 - 4 4 - 5 5 - 6 > 6

redshift

N

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Anton KoekemoerSummary

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~5-6Marginally inconsistent with extension of LDDE to z~6suggests 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