The spatial clustering of X-ray selected AGN at z~1

R. Gilli

Istituto Nazionale di Astrofisica (INAF) Osservatorio Astronomico di Bologna

and the XMM-COSMOS team

G. Zamorani, M. Brusa, N. Cappelluti, F. Civano, A. Comastri, F. Fiore, G. Hasinger,

V. Mainieri, T. Miyaji, J. Silverman et al.

On small scales (< 1 Mpc):What are the mechanisms triggering nuclear activity?Mergers (Hopkins +06), fly by (Cavaliere & Vittorini 00) or self regulating processes unrelated to galaxy interactions (Granato +04)? Any relation with star formation?

On large scales (>1 Mpc):What is the location of AGN within the cosmic web? In whichdark matter halos do they reside? What is their typical environment? Do obscured and unobscured AGN inhabit similarenvironments?

A few questions (for AGN at all redshifts and luminosities)

Put figure from li for agn and starforming galaxies..

Local SDSS narrow-line AGN

Star formation seems triggered by galaxy interactions, still no evidence for the majority of AGN

Li +07Projected cross-correlation function

AGNStar forming galaxies

Shen +07 (SDSS)

Optical QSOs at z>0

2QZ QSOs halo mass ~ constant ~ 3 1012 Msun

Even from the largest optical samples (2QZ, Porciani +06) there is still no clear evidence for any dependence of r0 on luminosity

2QZ

Goals

* Provide the best measurements to date of the correlation function of X-ray selected AGN

* Provide for the first time a reliable measurement of the correlation function of obscured AGN up to z~1 (so far only SDSS results for local, narrow line, optically selected AGN)

* Investigate the evolution with redshift and/or luminosity, AGN type

* Compare with galaxy clustering, estimate host galaxies

* Estimate masses of DM halos hosting X-ray nuclear activity

* Estimate lifetimes of X-ray selected AGN

* Estimate descendants of z~1 AGN

Large scatter (Vikhlinin +95, Basilakos +04, Gandhi +06, Puccetti +06, Miyaji +07, Basilakos +07). Dependence on flux/luminosity (eg Plionis +07)? Debated.Generation of random control samples problematic: uncertainties in the sensitivity maps.Also AGN redshift distribution is broad radial dimension usually much larger than the transverse dimension

Attempts to measure angular X-ray clustering

Plionis +07

X-ray fields with measured 3D clustering

Field Area/deg2 Slim[cgs] N/deg2 N(zspec) zmed logLmed Ref.

NEP 81 2 10-14 10 220 0.4 44.7 Mullis 03

BOOTES 9 5 10-15 350

COSMOS 2 7 10-16 900 620 1.0 43.8 in prep.

CLASXS 0.4 5 10-16 1500 230 1.1 43.8 Yang 05

CDFS 0.1 5 10-17 6000 130 0.8 43.0 Gilli 05

CDFN 0.13 2 10-17 8000 240 0.9 43.2 ’’

Surveys with different sensitivities sample different z and Lx regimesNeed large areas to cope with cosmic variance

XMM-COSMOS

CDF-S/N

CLASXS

0.1 deg2

0.4 deg2 2 deg2

Hasinger +07

Distribution of XMM-COSMOS AGN on the sky

1822 X-ray sources621 secure id and z-spec

Spectroscopic follow-up withIMACS@Magellanand VIMOS@VLT(also SDSS)

z-spec

Luminosity vs redshift distribution

z-spec only

I-band magnitude vs redshift

REFERENCE SAMPLE:538 X-ray selected objects with IAB<23 and 0.2<z<3.0

z-specz-phot

For IAB<23 completenessis ~60% and the redshiftdistribution of z-spec is similar to that of the global XMM sample

Redshift distribution of the reference sample:prominent spike at z~0.36

~40 AGNwith z=0.34-0.38

z~1 sample

Statistical description of LSS:the 2-point correlation function

Spatial Correlation Function:excess probability over random of finding a source in dV1 and

another in dV2 separated by a distance r

Projected correlation function w(rp):

Allows to get rid of distortions in redshift space(i.e. peculiar velocities, redshift errors)

πmax=40 Mpc/h, random control sample contains >20000 objects: same ra,dec of real sources, redshifts resampled from the observed smoothed distribution

The projected correlation function

All AGN r0 = 8.4 ± 0.4 γ = 1.9 ± 0.1

No spike r0 = 6.3 ± 0.6 γ = 1.9 ± 0.1

0.4<z<1.6 r0 = 5.7 ± 0.7 γ = 1.8 ± 0.1

Most significant clusteringmeasurement for X-rayselected AGN to date(~20σ Poisson errors~10σ Bootstrap errors)

Clustering dependence on optical type / X-ray absorption / redshift

BLAGNnon-BLAGN

High photon statistics reference sample

Clustering dependence on:

optical typer0 = 7.2 ± 0.9 r0 = 7.2 ± 0.8 γ = 2.0 ± 0.2 γ = 1.7 ± 0.2

X-ray absorptionr0 = 10.4 ± 0.5 r0 = 6.5 ± 0.9 r0 = 4.9 ± 1.7γ = 1.9 ± 0.1 γ = 1.8 ± 0.2 γ = 2.4 ±

0.7

redshiftr0 = 6.9 ± 1.0 r0 = 7.7 ± 0.4 r0 = 5.1 ±

0.7γ = 2.0 ± 0.2 γ = 1.8 ± 0.1 γ = 1.9 ±

0.2

No spike

The connection with host DM halos and galaxies

Halo catalogs from the Millennium simulation(Springel et al. 2005)

XMM-COSMOS AGN hostedby halos with M>3 1012 Msun/h

Their correlation length is similarto that of LIRGs and absorptionline galaxies at the same redshift(Coil +04, Gilli +07) moderately luminous z~1 AGNhosted by massive galaxieswith stellar mass > 3 1010 Msun

(see also Nandra +07, Silverman +08)

z~1 (0.4-1.6)

Clustering as a function of redshift

XMM-COSMOS AGN cluster similarly to optically selected QSOs at the same redshifts

Millennium halos

CDFS

AGN lifetime (tQ) from clustering

For XMM-COSMOS AGN (Lx~1044 erg/s; z~1): tQ ~ 3-6 108 yrThe estimated lifetime is longer by a factor of a few than thatof optically selected QSOs at the same redshift: this mainly reflectsthe higher space density of X-ray selected objects.

Two basic assumptions:1)QSOs reside in halos above a given halo mass threshold Mmin

2) there is one BH per halo

known from CDM models and N-body simulations

known from clustering

AGN space density, known from LF

Hosting halo density

Halo lifetime; eg assumed to be Hubble time at z

A simple scenario for clustering evolution

conserving scenario(Nusser & Davis 94, Fry 96Moscardini +98): objects with a given bias simply evolve withoutmerging along the density field

b2(z)=ξAGN/ξDM

b(z)= 1 + [b(0)-1]/D(z)

The relics of the accreting SMBHobserved in XMM-COSMOS willbe hosted by local bright(L~L*) ellipticals by z=0

z~1 sample

z~1 sample

Local ellipticals

Next: 1 deg2 Chandra-COSMOS

890 X-ray objectsfainter than XMM limit

Probe clustering at lower luminosities

Also with E-CDFS(~350 z-spec alreadyin hand)

Elvis +08Puccetti +08Civano +08Fiore +08

SummaryXMM-COSMOS provides 1) the most significant clustering measurement for X-ray selected AGN to date2) the first significant measurement of clustering of obscured AGN beyond the local

Universe

No significant differences between clustering of obscured and unobscured AGN

Presence of a significant redshift structure at z~0.36 which producesenhanced clustering signal at z<1

Clustering of XMM-COSMOS AGN at z~1 suggests they are hosted by massive galaxies, either passive or very actively starforming (LIRGs)

Halo host masses are M>3 1012 Msun, comparable to those obtained for optically selected QSOs at the same redshift

Estimated lifetimes are longer by almost an order of magnitude than those estimated for optical QSOs this reflects the higher space density of X-ray selected objects

The relics of the accreting SMBH observed in XMM-COSMOS will be hosted bylocal bright (L~L*) ellipticals by z=0