AGN Surveys

Phil Outram

University of Durham

17th February 2005

Cen A

Can observe many different types of AGN in many different wavebands

However, time is short…

So I’ll focus on optically-selected QSO (Luminous Type I AGN) surveys

Type I Type II

QSOs and Galaxy Formation

Studying QSOs Probes:– Accretion history of BHs in the Universe (S. White)– Relation of BH growth and galaxy evolution– Large Scale Structure Cosmology – State of intergalactic medium– History of reionization

In this talk I will outline some of the main results

from the 2dF & SDSS surveys…

QSO Surveys in the last decade

• 1996: Veron-Veron catalogue– 8609 QSOs– 2833 AGNs

• 2dF QSO survey (1997 – 2002)– 25,000 QSOs at z<3

• SDSS QSO survey (1999 – 2005+)– Currently: >50,000 QSOs– Goal: 100,000 QSOs– z<6.5

Selecting QSOs

• QSO candidates selected from multiband optical images• Identity confirmed (+ redshift measured) by spectroscopy• At z<2.5 QSOs typically blue stellar objects• Main contaminants include stars (inc. WDs) + NL galaxies• At low z, host galaxy may make QSO appear extended/redder• z>2.5 Ly forest makes QSO redder• 2.5<z<3 QSO colour similar to main sequence stars• Intrinsically reddened / ‘buried’ QSOs may be missed• Trade-off between COMPLETENESS & EFFICIENCY

z=0.1

z=0.3

z=1.3

z=2.0

z=2.5

z=3.0

z=3.8

z=4.5

z=5.0

z=6.43

The 2dF QSO Redshift Survey

3 Lya

2 CIV

CIII

MgII

1

OIII

0 4000 Å observed wavelength 8000 Å

reds

hift

Properties of 2QZ

•QSOs selected from stellar sources using U-B:B-R colours•0.3<z<2.5•~23000 B<21 QSOs in final catalogue•Volume probed ~4 x109h-3Mpc3

www.2dfquasar.org

Croom et al. 2002, MNRAS, 322, L29

Croom et al. 2004, MNRAS, 349, 1397

The 2dF QSO The 2dF QSO Redshift SurveyRedshift Survey

The SDSS QSO SurveyThe SDSS QSO Survey

NGP SGP QSOs selected from imaging in 5 wavebands – u g r i z

Multi-colour selection Sensitive to QSOs at high redshift (z<6.5)

Currently ~50000 QSOs in DR3

i<19 (main sample) i<20 (high-z sample)Schneider et al. 2003, AJ, 126, 2579

www.sdss.org

Evolution of Quasar Evolution of Quasar Luminosity FunctionLuminosity Function

SFR of Normal Gal

Strong evolution in luminosity density is seen back to z~2.

At z>3 the observed space density of QSOs declines.

Exponential decline of quasar density at high redshift, different from normal galaxies

Evolution of LF shapeEvolution of LF shape

PLEPDE

At low-z: LF is well fit by double power law with pure luminosity evolution

PLE A single population of rare, long-lived QSOs?

At z~4: quasar At z~4: quasar luminosity function luminosity function much FLATTERmuch FLATTER than than LF at z~2LF at z~2

Due to the relatively bright magnitude limits of the SDSS and 2QZ surveys, the LF analysis is restricted to relatively bright QSOs – especially at high redshift.

What about fainter QSOs?

2SLAQ survey extending 2QZ a magnitude deeper:~10000 g<21.85 QSOs on the way…

Photometric selection of 192 1.2<z<4.8 QSOs using COMBO-17, reaching R~24

Wolf et al. (2003)

COMBO-17

The evolving LF can be adequately described by either PLE (dashed line) or PDE (solid line) – largely due to the absence of an obvious break

QSO Clustering

Croom et al. 2004

Do QSOs trace: the large scale structure of dark matter, the distribution of normal galaxies, or, just the most overdense regions (a highly-biased distribution)?

We can answer this question by determining the amplitude of QSO clustering

The 2-Point Correlation Function

Redshift Evolution

2dF

Fan et al. Croom et al. 2004

Decreasing bias upper limit to lifetime of QSOs ≲ 6x108 years at z~2

2dF QSO clustering

amplitude at fixed z vs

MB

(Loaring et al. in prep)

BLR Emission Line Widths

Corbett et al 2003, MNRAS, 343, 705

Measure v & apply virial theorem: MBH ~ R v 2

Assume: R ~ L 0.68

- observed locally (Netzer 2002)

where R is the BLR radius.

MBH ~ v 2 L 0.68

Line widths MBH ~ L0.93

Assuming that radius-Luminosity relation independent of z then can derive M/L evolution:

Little evolution in M/L seen

This also does not agree with PLE

Caveat…

Large L ( R) evolution seen, but what if R ~ M not L??

Evolution in BH mass function

McLure & Dunlop 2003

QSO BH masses appear to drop towards lower redshift! (“Downsizing”)

However… Direct imaging host galaxies do not appear any larger at high redshift (e.g. Croom et al 2004)

Understanding QSOs: summary of evidence so far…Locally: QSOs cluster like average galaxies

z~2: higher clustering amplitude + MUCH more luminous / numerous

Little correlation between luminosity / clustering amplitude

QSOs seen out to z>6

LF well described by PLE

QSO BH mass as z ?

BHs seen in ALL bulges – tight correlation:

Possible scenario…In hierarchical galaxy merging paradigm - all major galaxies have short-lived QSO phase:

QSO lit up when gas funnelled into galaxy centre after merger

QSO stage when halo has mass ~ 1012-13 Mס ~ constant with z

Fewer mergers, less gas around now – fewer, lower L QSOs

Semi-Analytic models

Outram et al. 2003, MNRAS, 342, 483

Need to assume cosmology to derive r from z

Power spectra convolved with survey window functions

On to cosmology…The 2QZ Power Spectrum

Comparison with models

Mock QSO P(k) from Hubble Volume ΛCDM N-body simulation

Fitting model CDM P(k)

Ωmh=0.19±0.05 Ωb/Ωm=0.18±0.10

Redshift-space Distortions in the QSO Power Spectrum

Outram et al. 2001, MNRAS, 328, 174

Ωm=1-ΩΛ=0.29

β=0.45

Outram et al. 2004, MNRAS, 348, 745

+0.17

-0.09

+0.09

-0.11

An EdS cosmology is rejected at over 95% confidence.

z-space distortion effect of cosmology / infall degenerate…

However, we have a second constraint on the bias (and hence infall) from the correlation function analysis

Gravitational lensing of distantQSOs by foreground galaxies

Cross-correlation of QSOs with foreground galaxies

Myers et al. 2005, submitted Gaztanaga, 2003, ApJ, 589, 82

Stronger signal seen than expected!

Optical depth fluctuations in observed spectra monotonically mapped onto a Gaussian density field.

Bias-free linear P(k) estimate at 2<z<5

McDonald et al. (2004)

3000 SDSS spectra

The Ly Forest Power Spectrum

Kim et al. (2004) – LUQAS QSOs from UVES - 27 high-resolution QSO spectra

Large uncertainty in normalization due to uncertainty in continuum & hence optical depth – especially in low resolution spectra.

The Highest Redshift QSOs

• z>4: ~700 known • z>5: ~30 • z>6: 7 • SDSS i-dropout Survey:

– By Spring 2004: 6000 deg2 at zAB<20

– Fourteen luminous quasars at z>5.7

• 20 – 40 at z~6 expected in the whole survey

SDSS DiscoveriesTotal Discoveries

Constraining the Reionization Epoch

• Neutral hydrogen fraction– Volume-averaged HI fraction

increased by >100 from z~3 to z~6

– Mass-averaged HI fraction > 1%

• At z~6: – Last remaining neutral regions

are being ionized– The universe is >1% neutral

The end of reionization epoch?? Fan et al. in prep

mass ave.

vol. ave

QSOs and Galaxy Formation

Studying QSOs Probes:

– Accretion history of BHs in the Universe

– Relation of BH growth and galaxy evolution

– Large Scale Structure Cosmology

– State of intergalactic medium

– History of reionization