The spatial clustering of Xray selected AGN at z1

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The spatial clustering of X-ray selected AGN at
z1

• 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.

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A few questions (for AGN at all redshifts and
luminosities)
On small scales (lt 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 (gt1 Mpc) What
is the location of AGN within the cosmic web? In
which dark matter halos do they reside? What is
their typical environment? Do obscured and
unobscured AGN inhabit similar environments?
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Local SDSS narrow-line AGN
Projected cross-correlation function
Li 07
Put figure from li for agn and starforming
galaxies..
AGN
Star forming galaxies
Star formation seems triggered by galaxy
interactions, still no evidence for the majority
of AGN
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Optical QSOs at zgt0
Shen 07 (SDSS)
2QZ
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
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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 z1 (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 z1 AGN
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Attempts to measure angular X-ray clustering
Plionis 07
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
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X-ray fields with measured 3D clustering

• Field Area/deg2 Slimcgs 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 regimes Need large areas to
cope with cosmic variance
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XMM-COSMOS

CDF-S/N
0.1 deg2
CLASXS
2 deg2
0.4 deg2
Hasinger 07
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Distribution of XMM-COSMOS AGN on the sky
z-spec
1822 X-ray sources 621 secure id and
z-spec Spectroscopic follow-up
with IMACS_at_Magellan and VIMOS_at_VLT (also SDSS)
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Luminosity vs redshift distribution
z-spec only
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I-band magnitude vs redshift
For IABlt23 completeness is 60 and the
redshift distribution of z-spec is similar to
that of the global XMM sample ?
z-spec z-phot
REFERENCE SAMPLE 538 X-ray selected objects
with IABlt23 and 0.2ltzlt3.0
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Redshift distribution of the reference
sampleprominent spike at z0.36
40 AGN with z0.34-0.38
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Statistical description of LSSthe 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)
pmax40 Mpc/h, random control sample contains
gt20000 objects same ra,dec of real sources,
redshifts resampled from the observed smoothed
distribution
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The projected correlation function
Most significant clustering measurement for
X-ray selected AGN to date (20s Poisson
errors 10s Bootstrap errors)
All AGN r0 8.4 0.4 ? 1.9 0.1 No
spike r0 6.3 0.6 ? 1.9 0.1 0.4ltzlt1.6
r0 5.7 0.7 ? 1.8 0.1
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Clustering dependence on optical type / X-ray
absorption / redshift
High photon statistics
reference sample
BLAGN non-BLAGN
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Clustering dependence on optical type r0 7.2
0.9 r0 7.2 0.8 ? 2.0 0.2 ?
1.7 0.2 X-ray absorption r0 10.4 0.5 r0
6.5 0.9 r0 4.9 1.7 ? 1.9 0.1 ?
1.8 0.2 ? 2.4 0.7 redshift r0 6.9
1.0 r0 7.7 0.4 r0 5.1 0.7 ? 2.0
0.2 ? 1.8 0.1 ? 1.9 0.2
No spike
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The connection with host DM halos and galaxies

• Halo catalogs from
• the Millennium simulation
• (Springel et al. 2005)
• XMM-COSMOS AGN hosted
• by halos with Mgt3 1012 Msun/h
• Their correlation length is similar
• to that of LIRGs and absorption
• line galaxies at the same redshift
• (Coil 04, Gilli 07) ?
• moderately luminous z1 AGN
• hosted by massive galaxies
• with stellar mass gt 3 1010 Msun
• (see also Nandra 07, Silverman 08)

z1 (0.4-1.6)
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Clustering as a function of redshift
XMM-COSMOS AGN cluster similarly to optically
selected QSOs at the same redshifts
CDFS
Millennium halos
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AGN lifetime (tQ) from clustering
Two basic assumptions 1)QSOs reside in halos
above a given halo mass threshold Mmin 2) there
is one BH per halo

• For XMM-COSMOS AGN (Lx1044 erg/s z1) tQ 3-6
  108 yr
• The estimated lifetime is longer by a factor of a
  few than that
• of optically selected QSOs at the same redshift
  this mainly reflects
• the higher space density of X-ray selected
  objects.

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A simple scenario for clustering evolution
conserving scenario (Nusser Davis 94, Fry
96 Moscardini 98) objects with a given bias
simply evolve without merging along the density
field b2(z)?AGN/?DM b(z) 1
b(0)-1/D(z) The relics of the accreting
SMBH observed in XMM-COSMOS will be hosted by
local bright (LL) ellipticals by z0
z1 sample
Local ellipticals
z1 sample
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Next 1 deg2 Chandra-COSMOS
Elvis 08 Puccetti 08 Civano 08 Fiore 08
890 X-ray objects fainter than XMM limit
Probe clustering at lower luminosities Also
with E-CDFS (350 z-spec already in hand)
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Summary

• XMM-COSMOS provides
• 1) the most significant clustering measurement
  for X-ray selected AGN to date
• 2) 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
  z0.36 which produces
• enhanced clustering signal at zlt1
• Clustering of XMM-COSMOS AGN at z1 suggests they
  are hosted by massive
• galaxies, either passive or very actively
  starforming (LIRGs)
• Halo host masses are Mgt3 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