Clustering of QSOs and X-ray AGN at z=1

Alison CoilAlison CoilHubble FellowHubble Fellow

University of ArizonaUniversity of Arizona

October 2007October 2007

Collaborators: Jeff Newman, Joe Hennawi, Marc Davis, Paul Nandra, Antonis Georgakakis

Main Points

1. Different QSO/AGN formation theories predict different clustering properties - amplitude as f(z,L). Clustering constrains models (even w/ current error bars).

2. Clustering constrains the mass of the host DM halo and host galaxy type and timescale between evolutionary stages.

3. Cross-correlating with large samples of galaxies rather than using QSO/AGN samples alone gives small errors - both Poisson and cosmic variance - and allows measures on small scales. Only need selection function of galaxies, not AGN.

4. Results: QSOs cluster like blue/star-forming galaxies, not red galaxies, at z~1.

5. Results: X ray-selected AGN cluster like red galaxies at z~1 (more clustered than QSOs).

Clustering Information

What you can learn from clustering:

close pairs / interactions / mergersradial profiles of galaxies/AGN w/in halos

host dark matter halo masshalo occupation distribution function

what kinds of galaxies host AGNtrace evolving populations through different z’s

connect different samples and z’sconstrain timescales between different evolutionary stages

compare with AGN formation and evolution models

Very helpful to know clustering of galaxies at the same redshift, in the same volume, as a function of color/luminosity.

Galaxy Clustering: Luminosity, ColorBrighter r0 > Fainter r0 + Redder r0 > Bluer r0

At z=0 and z=1

z=0.9:(for ~L* galaxies:)redred: r0=5.2 Mpc/h =2.0 b=1.6 Mmin=2 1012 Mo/h

blue: r0=3.8 Mpc/h =1.7 b=1.3 Mmin=5 1011 Mo/h

Coil et al 2006Coil et al 2008

clu

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ing

am

plit

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separation - rp

luminositycolor

QSO+AGN clustering - z~1

DEEP2 is a completed redshift survey using the Keck II telescope, covering multiple fields on the sky (for cosmic

variance) to study galaxy evolution and LSS at z=0.7-1.5. Sample is selected to R=24.1.

DEEP2 has a high sampling rate (60%) and precise redshifts (<30 km/s) - good for clustering and environments. Full

sample has >40,000 galaxies in V~3x106 Mpc3/h3.

One field is the Extended Groth Strip (EGS), which has 8 Chandra pointings of 200 ks each over a 2 x 0.25 degree field.

(Chandra team: K. Nandra, A. Georgakakis, E. Laird)

SDSS QSOs in DEEP2 fields

36 SDSS + 16 DEEP2 spectroscopic broad-line QSOs in the DEEP2 fields between z=0.7-1.4:

SDSS

DEEP2

(near M*)

MB

redshift

Clustering of Galaxies around QSOsClustering of DEEP2 galaxies around SDSS QSOs at z=0.7-1.4.

Errors include Poisson errors + cosmic variance (from mocks).

Similar errors as surveys with 1000s of QSOs (eg. 2dF) through use of cross-correlation with 10,000s of galaxies.

Divide by the clustering of DEEP2 galaxies around DEEP2 galaxies to get the relative bias of QSO hosts…

Coil et al. 2007 ApJseparation

0.1 Mpc/h 10 Mpc/h

Relative bias of QSOs to DEEP2 galaxiesQSO relative bias = 0.9 (0.2)

QSO absolute bias = 1.2 (0.3)

Cluster like blue galaxies not red!

Constrains host type for QSOs (blue) and QSO host halo masses:

Min. halo mass = 5x1011 M0/h

Mean halo mass = 3x1012 M0/h

No dependence is seen on magnitude (MB=-22.8 vs -24.1) or redshift (z=0.7-1.0 vs 1.0-1.4)

Coil et al. 2007 ApJ

group clustering: Mmin= 6 x 1012 M0/hr0=6.2 (0.4) Mpc/h =1.5 (0.2)

Comparison w/ 2dF+SDSS:

Our QSO clustering amplitude is ~1lower than other results (with 20% errors). Done for free by having galaxy

redshifts in SDSS QSO fields.

Clustering of X-ray AGN

-24-16 MB

color

red

Nandra et al. 2006 ApJL

Chandra survey in the EGS: 200 ks depth

Have ~10,000 galaxies and ~250 (so far) X-ray sources

w/ z=0.2-1.41/2 from DEEP2 (R=24.1)

1/2 from MMT (R=23)

X-ray AGN hosts are bright and on red sequence or

massive end of blue cloud. (even the faint ones: Lx~1042-

44 erg/s)Log Eddington ratio=

-2.5 to -4.0

quasars

z=0.7-1.4

blue

ACS Imaging of X-ray AGN

~60% of hosts have early-type morphologies

(Pierce et al. 2007)

Not dominated by major mergers but early-types

do show more minor merger asymmetry than

normal ellipticals(Georgakakis et al. 2007,

submitted)

(to my untrained eye, ~50% spheroids

~33% spirals~10% mergers/Irr

9% blue point sources)

Clustering of X-ray AGNSplit into 2 redshift bins: z=0.2-0.7 and z=0.7-1.4

X-ray AGN cluster like red galaxies, not blue galaxies, at both z~0.5 and z~0.9

Coil et al. in prep

Relative bias of X-ray AGN to galaxies:z=0.7-1.4 red gals: 1.1 (0.1) blue gals: 1.7 (0.1)z=0.2-0.7 red gals: 1.1 (0.1) blue gals: 1.4 (0.1)

Jacknife errors for now - will update w/ simulations

Clustering of X-ray AGN

AGN on red sequence are more clustered than in blue cloud

Coil et al. in prep

Relative bias of red to blue AGN:z=0.7-1.4 red/blue AGN=1.5z=0.2-0.7 red/blue AGN=1.3

Similar to galaxy red/blue relative bias=1.4

Relative bias of brighter to fainter AGN:

z=0.7-1.4 MB= -21.3/-20.5 bias=1.2z=0.2-0.7 MB= -20.7/-19.8 bias=1.2

Similar to galaxy bright/faint bias for same magnitude range - 1.2

(errors may be too large to make this statistically significant)

Clustering of X-ray AGN

Results: - split into 2 z bins - same results at z~0.5 and z~0.9- X-ray AGN cluster like red galaxies, not blue

galaxies - X-ray AGN are more clustered than QSOs! - red AGN are more clustered than blue AGN

Consistent w/ galaxies undergoing a QSO phase before settling on the red sequence w/ an X-ray AGN

Coil et al. in prep

QSO/AGN Evolution Models

Competing QSO/AGN formation and evolution models predict different clustering properties.

All assume major mergers trigger QSO formation.

- Kauffmann and Haenelt 2001 predict a strong luminosity-dependence to QSO clustering:

- assume an exponentially declining light curve, time=- M_B ~ gas mass accreted / - gas mass accreted ~ host halo mass - luminosity~halo mass

brighter QSOs cluster much more

ruled out by clustering observations

QSO/AGN Evolution Models

Lidz, Hopkins predict less luminosity-dependence (still some) - bright and faint QSOs have similar clustering - bias predicted at z~1 is a bit too high (b~2) - would predict X-ray AGN cluster like quasars (?)

Croton et al. 2006 include a ‘radio’ mode for low-L AGN - if halo M > Mthreshold then no cold gas accretion, shuts off SF - no

QSO - but there is a low-L AGN fed by hot gas - predict blue galaxies have QSOs and red galaxies have low-L AGN - good qualitative agreement with our results

Scannapieco + Thacker 2006 model predicts both auto- and cross-correlation of QSO and matches our z=1 cross-correlation very well! Have their QSOs in the right halos and galaxies at z=1.

Conclusions

1. QSOs are less clustered than X-ray selected AGN at z~1.

2. QSOs cluster like blue star-forming galaxies while AGN cluster like red quiescent galaxies (overdense regions).

3. Red galaxies w/ AGN are more clustered than blue galaxies w/ AGN.

4. These results favor galaxies undergoing a bright QSO phase before settling on the red sequence with a lower luminosity AGN.

5. Possibly QSO=early merger phase, X-ray AGN=later merger phase.

Measuring QSO/AGN clustering in fields with galaxy redshiftsallows cross-correlation (small scales with small errors) and

environment measures. Compare with red and blue galaxies at the same z and in the same volume (cosmic variance ~cancels).