AGN Surveys Phil Outram University of Durham 17 th February 2005.
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Transcript of AGN Surveys Phil Outram University of Durham 17 th February 2005.
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AGN Surveys
Phil Outram
University of Durham
17th February 2005
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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
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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…
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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
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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
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z=0.1
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z=0.3
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z=1.3
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z=2.0
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z=2.5
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z=3.0
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z=3.8
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z=4.5
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z=5.0
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z=6.43
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The 2dF QSO Redshift Survey
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3 Lya
2 CIV
CIII
MgII
1
OIII
0 4000 Å observed wavelength 8000 Å
reds
hift
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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
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The 2dF QSO The 2dF QSO Redshift SurveyRedshift Survey
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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
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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
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Evolution of LF shapeEvolution of LF shape
PLEPDE
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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
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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
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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
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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
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Redshift Evolution
2dF
Fan et al. Croom et al. 2004
Decreasing bias upper limit to lifetime of QSOs ≲ 6x108 years at z~2
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2dF QSO clustering
amplitude at fixed z vs
MB
(Loaring et al. in prep)
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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
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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??
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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)
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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
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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
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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
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Redshift-space Distortions in the QSO Power Spectrum
Outram et al. 2001, MNRAS, 328, 174
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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
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Gravitational lensing of distantQSOs by foreground galaxies
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Cross-correlation of QSOs with foreground galaxies
Myers et al. 2005, submitted Gaztanaga, 2003, ApJ, 589, 82
Stronger signal seen than expected!
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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
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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.
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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
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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
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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