The environment of AGN at z~1
Antonis Georgakakis
Imperial College
K. Nandra & the AEGIS collaboration
Motivation
Role of environment in AGN formation/evolution:
– Merger models (e.g. Hopkins et al. 2005), less
dense regions (field, group)
– AGN suppress cooling flows in relatively
dense environments, group/cluster (“radio-
mode”; Croton et al. 2006)
At the edge of the Universe, Sintra 2006
Motivation
• At z~0.1 optically selected luminous AGN in the field (Kauffmann et
al. 2004)
• At higher-z controversy on Large Scale Structure of AGN:
– X-ray selection, correlation length: ro=5–10h-1Mpc @ z~1 (e.g. Basilakos et al.
2004, 2005; Gilli et al. 2005; Yang et al. 2006)
– Optical selection, correlation length: ro~5h-1Mpc @ z~1.5 (e.g. 2QZ, Croom et al.
2005)
– Broad-line QSOs at z~1 are weakly clustered, like the field blue galaxy
population (Coil et al. 2006)
• Discrepancy because of:
– cosmic variance, small number statistics
– selection method (e.g. X-ray, optical)
At the edge of the Universe, Sintra 2006
All-wavelength Extended Groth
strip International Survey
• Multi-wavelength sample &
wide area (0.5deg2; ~15Mpc
at z~1)
• DEEP2: 9000 redshifts,
(R0.7) hosts
At the edge of the Universe, Sintra 2006
Environment estimator: projected
surface density (3)
Cooper et al. 2005, 2006a, b
• Pick X-ray source
• Search for neighbours
within Δv=1000km/s
• r3: projected distance
to 3rd nearest
r3 neighbour.
• projected density:
3=3/πr23
3rd nearest neighbor
At the edge of the Universe, Sintra 2006
X-ray selected AGN: density vs MB
Georgakakis et al. 2006; Cooper 2006a, b
X-ray selected AGN at z~1: dense environment
At the edge of the Universe, Sintra 2006
X-ray selected AGN: density vs U-
B
Georgakakis et al. 2006; Cooper 2006a, b
X-ray selected AGN at z~1: similar environment
to optical galaxies of similar U–B colour
At the edge of the Universe, Sintra 2006
Conclusions
• X-ray selected AGN at z~1:
– hosted by luminous/red galaxies,
– avoid below-average density regions,
– unbiased relative to galaxies of similar type (i.e. U-B).
• BUT z~0.1 luminous AGN are in the field:
– high density regions more active at z~1,
– different selection, i.e. X-ray vs optical.
• AEGIS provides multi-λ coverage to:
– select AGN at different wavebands: X-ray, IR, radio, optical,
– explore possible differences in their environment.
At the edge of the Universe, Sintra 2006
Dependence on LX
Dependence on MB
• results not affected by
X-ray flux limit
• MB dependence real
Environment estimator: projected
surface density (3)
Cooper et al. 2005, 2006
• Pick X-ray source
• Search for neighbors
X-ray source, z=0.9972 within Δv=1000km/s
• rpr,3: projected distance
to 3rd nearest neighbor.
• 3=3/πr2pr,3: projected
density
• Redshift effects:
normalise by median 3
at z of source
Environment estimator: projected
surface density (3)
Cooper et al. 2005, 2006
• Pick X-ray source
• Search for neighbors
Δv=1000km/s within Δv=1000km/s
• rpr,3: projected distance
to 3rd nearest neighbor.
• 3=3/πr2pr,3: projected
density
• Redshift effects:
normalise by median 3
at z of source.
Environment estimator: projected
surface density (3)
Cooper et al. 2005, 2006
• Pick X-ray source
• Search for neighbors
within Δv=1000km/s
• rpr,3: projected distance
to 3rd nearest neighbor.
• 3=3/πr2pr,3: projected
density
• Redshift effects:
normalise by median 3
at z of source.
3rd nearest neighbor
Environment estimator: projected
surface density (3)
Cooper et al. 2005, 2006
• Pick X-ray source
• Search for neighbors
within Δv=1000km/s
• rpr,3: projected distance
to 3rd nearest neighbor.
• 3=3/πr2pr,3: projected
density
• Redshift effects:
normalise by median 3
at z of source.
projected density within circle
All-wavelength Extended Groth
strip International Survey
• Multi-wavelength sample &
wide area (0.5deg2; ~15Mpc
at z~1)
• DEEP2: 9000 redshifts,
(R<24.1 to z=1.4)
• Deep Chandra data:
– Optimal for AGN selection
– 200ks per pointing
– LX~1042erg/s @ z~1 AEGIS
0.5deg2
At the edge of the Universe, Sintra 2006
All-wavelength Extended Groth
strip International Survey
• Multi-wavelength sample &
wide area (0.5deg2; ~15Mpc
at z~1)
• DEEP2: 9000 redshifts,
(R<24.1 to z=1.4)
• Deep Chandra data:
– Optimal for AGN selection
– 200ks per pointing
– LX~1042erg/s @ z~1 AEGIS
0.5deg2
At the edge of the Universe, Sintra 2006