the spatial clustering of x-ray selected agn r. gilli istituto nazionale di astrofisica (inaf)...
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![Page 1: The spatial clustering of X-ray selected AGN R. Gilli Istituto Nazionale di Astrofisica (INAF) Osservatorio Astronomico di Bologna On behalf of the CDFS](https://reader036.vdocuments.net/reader036/viewer/2022062313/56649d555503460f94a31ead/html5/thumbnails/1.jpg)
The spatial clustering of X-ray selected AGN
R. Gilli Istituto Nazionale di Astrofisica (INAF) Osservatorio Astronomico di Bologna
On behalf of the CDFS and COSMOS teams
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AGN clustering…
•AGN can trace the Large Scale Structure of the Universe to cosmologically significant redshifts (z>1-2)
•AGN physics from clustering: e.g. host halo mass and lifetimes
Also used to estimate the host galaxy type
…in the X-ray band
•X-rays efficiently sample obscured AGNs (which outnumberunobscured ones by a factor of at least 3-4; see XRB synthesisand the results from the deep surveys) •High surface density, above 1000-2000 sources/deg2, even in moderately deep surveys high clustering significance with relatively small number of objects
e.g. Croom 05, Porciani 05 Martini & Weinberg 01
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AGN clustering as a function of..
1) redshift: measured for optical QSOs
r0 increases with redshift halo mass ~ constant ~ 3 1012 Msun
(e.g 2dF – Croom et al. 04,05 ; Porciani et al. 05,06)
2) luminosity: still to be measured3) obscuration: still to be measured
From optical and X-ray studies (Yang 05) there is no clearevidence for any dependence of r0 on L. Similarly, there is noevidence yet for any dependence of r0 on obscuration (X-raysamples still small)
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X-ray fields with measured 3D clustering
Field Area/deg2 Slim[cgs] N/deg2 N(zspec) zmed logLmed Ref.
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 ’’
CLASXS 0.4 5 10-16 1500 230 1.2 43.9 Yang 05
COSMOS 2 7 10-16 1000 380 1.0 44.1 in prep.
NEP 81 2 10-14 10 220 0.4 44.7 Mullis 03
Surveys with different sensitivities sample different z and Lx regimes: one needs to always specify at which average z and Lx clustering is computed
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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
ξ(r) increases at small separations, then one needs either deep fields in which the source density is very high or large volumes – or, preferably, both
Projected correlation function w(rp):
Allows to get rid of distortions in redshift space(i.e. peculiar velocities, redshift errors)
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Expected 3D clustering significance in X-ray surveys
SNR=(DD-RR)/RR0.5
Where DD and RR are thenumbers of data-data andrandom-random pairs within agiven separation (e.g. 10 Mpc)
SNR ≈ V-0.5 N
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3D correlation function in the Chandra Msec fields
CDFS r0=10.3±1.71.33±0.14
CDFN r0=5.5±0.6
1.50±0.12
unabsorbed AGN
absorbed AGN
CDFS vs CDFN AGN CDFN: abs vs unabs AGN
Large variance between the twoChandra Msec fields
No statistically significant differencebetween clustering of obscured andunobscured AGN within a single CDF
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Comparing redshift distributions
CDFS
30% of sources in the 2 most prominent spikes
13%
6%
CDFN
CLASXS COSMOS5-8%
Due to redshift spikes, cannot divide in z–bins in the CDF-S/NNeed large area to avoid cosmic variance
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XMM-COSMOS
CDF-S/N
CLASXS
0.1 deg2
0.4 deg2 2 deg2
First XMM-COSMOS results: Hasinger 06, Cappelluti 06, Brusa 06, Mainieri 06, Miyaji 06, Finoguenov 06
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Preliminary measurements in COSMOS
unobscuredobscured
Based on Hardness Ratios
All sources
r0 = 7.3 ± 0.5γ = 1.8 ± 0.1
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Clustering of ~ obscured vs unobscured AGN
No statistical evidence for any difference. Based on hardness-ratios: need to be done using NH measurements from spectral fits
unobscuredobscured
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AGN Correlation length vs redshift(and luminosity)
Late,early type r0 from Coil et al. 03
late
early
Halo catalogs fromKauffman et al. 99
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Summary• Spatial clustering of X-ray selected AGN has been measured so far
in only 5 fields. Large cosmic variance is observed between the two pencil beam Chandra Msec fields. Need large areas to get an “unbiased” estimate of AGN clustering and need large
area x Nsources product (i.e. large and sensitive surveys) to measure clustering signal at high significance.
• Within each field no significant difference is found between the clustering properties of obscured and unobscured AGN (but check
using X-ray spectra rather than HR).
• X-ray selected AGN appear hosted by halos with mass larger than 1-2 x 1012 Msun
• At z~1 the AGN correlation length is in between that of early and late type galaxies at the same redshift (but large scatter: COSMOS ~ early).