Gordon Richards Drexel University With thanks to Michael Strauss Yue Shen Princeton Don Schneider Nic Ross Penn State Adam Myers Illinois Phil Hopkins Berkeley and a host of other people from the SDSS Collaboration ID: 555688
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Slide1
The Build-up of Quasars
Gordon RichardsDrexel University
With thanks to
Michael Strauss,
Yue
Shen
(Princeton), Don Schneider, Nic Ross (Penn State), Adam
Myers (Illinois
), Phil Hopkins (
Berkeley
),
and a host of other people from the SDSS CollaborationSlide2
Caveats
I tend to be biased towards: High redshift (z>1)
High luminosity
Optical Selection
“Quasar” mode accretion
Unobscured
(i.e., type 1)
Quasar=QSO=AGN=
any actively accreting
supermassive
black holeSlide3
The Redshift Desert
Redshift desert for galaxies due to lack of spectral features in the optical octave at z~2. No redshift desert for quasars (in the galaxy sense), but there is in reality. And just as frustrating.
Galaxy
Quasar
Franx
2003Slide4
The z~2.7 Quasar Desert
Schneider et al. 2007Observed
CorrectedSlide5
Z~2.7 Quasar Colors
At 2.5<z<3.0 quasars cross through the locus of stars, making those quasars harder to identify (efficiently).Slide6
X-ray and IR Selection
X-ray and IR selection don’t suffer from the same problem (and they allow selection of obscured quasars). But they do have their own problems. Area surveyed by X-ray is tiny.
Mid-IR has its own 3.5<
z
<5 desert.
Not clear that optical/radio/MIR/X-ray selecting same o
bjects (at least at lower luminosity), see
Hickox
et al. 2008.Slide7
Quasar Luminosity Function
As with star formation rate, quasars peaked at redshift 2-3.
Richards et al. 2006
The rise and fall is even more dramatic in time than redshift.Slide8
The Rise of Quasars at z~6
Mere existence z~6 quasars constrains formation models
Eddington argument: If the luminosity of a quasar is high enough, then radiation pressure from electron scattering will prevent further gravitational infall.
L
E
= 1.38x10
38
M/M
sun
erg/s
M
E
= 8x10
7
L
46
M
sun
Sets an upper limit to the luminosity for a given mass, or
equivalently
a minimum mass for a given luminosity.Slide9
Making SMBHs at z~6
The luminosities of the z~6 quasars imply BH masses in excess of 109 M
Sun
.
But z~6 is <1Gyr after the Big Bang.
Assembling that much mass in so little time is difficult (but not impossible).
Tanaka &
Haiman
2009Slide10
Quasar Luminosity Function
SDSS is relatively shallow. It probes only the tip of the iceberg.
Need fainter surveys to get full picture.
e.g., Richards et al. 2006Slide11
Cosmic Downsizing
Ueda et al. 2003
Hasinger
et al. 2005
X-ray surveys probe much deeper. Here we see that peak depends on the luminosity.Slide12
Cosmic Downsizing
Hasinger et al. 2005
X-ray surveys probe
much
larger dynamic range.
SDSS+2SLAQ
Croom
et al. 2009Slide13
How does the quasar luminosity function relate to the physics of BH accretion and galaxy evolution?Slide14
Quasar Luminosity Function
Croom et al. 2004
Space density of quasars as a function of redshift and luminosity
Typically fit by double power-lawSlide15
Density Evolution
Number of quasars is changing as a function of time.Slide16
Luminosity Evolution
Space density of quasars is constant.
Brightness
of
individual (long-lived)
quasars is changing.Slide17
Luminosity vs. Redshift
Usually we split into L or z
instead of making a 3-D plot, but the information is the same.
0.5
1.5
2.5
3.5
4.5Slide18
Luminosity Evolution
Pure density or pure luminosity evolution don’t lead to cosmic downsizing.
The slopes
must
evolve with redshift.
Cosmic DownsizingSlide19
Luminosity Dependent Density Evolution
To get cosmic downsizing, the number
of
quasar must change
as a function of time, as a function of
luminosity. i.e., the slopes must evolve.Slide20
Bolometric QLF
Hopkins, Richards, & Hernquist 2007Slide21
Hopkins et al. 2005
Hopkins et al. 2006Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity hierarchy.
Hopkins et al.: quasar phase is episodic with a much smaller range of mass than previously thought.
QLF is the
convolution
of the formation rate and the lifetime.Slide22
QSO QLF != Galaxy QLF
Benson et al. 2003Slide23
Hopkins et al. 2005
Hopkins et al. 2006Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity hierarchy.
Hopkins et al.: quasar phase is episodic and “all quasars are created equal” (with regard to mass/peak luminosity).
QLF is the
convolution
of the formation rate and the lifetime.Slide24
Merger Scenario w/ Feedback
merge gas-rich galaxies form buried
quasars
feedback
expels the
gas
revealing
the
quasar
shutting
down
accretion and star formation
Granato
et al. 2004,
DiMatteo
et al. 2005,
Springel
et al. 2005, Hopkins et al. 2005/6a-z
e.g., Kauffmann &
Haehnelt
2000Slide25
How Can We Test This?
The Quasar Luminosity Function active lifetime (e.g., Martini 2004) accretion rate (
e.g.,
Kollmeier
et al. 2006
)
M
BH
distribution (
e.g.,
Vestergaard &
Osmer 2009)
Quasar Clustering
L,
z
dependence (
e.g.,
Lidz
et al. 2006 ;
Shen
et al. 2009
)
small
scales (
e.g.,
Hennawi
et al. 2006; Myers et al. 2008
)
In addition to the evolution of the QLF slopes, we can probe:Slide26
Clustering
Red Points are, on average, randomly distributed, black points are clusteredRed points: (
)=0
Black points:
(
)>0
Can vary as a function of, e.g., angular distance,
(blue circles)
Red:
(
)=0 on all scales
Black:
(
) is larger on smaller scales
A. MyersSlide27
Quasar Clustering
Quasars are more clustered on small scales than large scales.
Comparing with models of dark matter clustering gives the “bias” (
overdensity
of galaxies to DM)
Linear bias (
b
Q
=
1
) ruled out at high
significance.
Myers et al. 2007Slide28
Galaxy Clustering
The comoving clustering length of luminous galaxies is roughly independent of z at least to z ~ 5. Therefore, the distribution of galaxies must be increasingly biased relative to the dark matter at high redshift,
galaxies
=
b
dark
matter
Ouchi
et al. 2004Slide29
How about quasars?
Quasars are powered by the ubiquitous super-massive black holes in the cores of ordinary massive galaxies
Therefore, we’d expect that the clustering of quasars should be similar to that of luminous galaxies, at the same redshift.
Bahcall
,
Kirhakos
et al.Slide30
Comoving Correlation Length
Ross et al. 2009
SDSS QuasarsSlide31
Quasar Bias Evolution
Ross et al. 2009As with galaxies, constant clustering length means strongly evolving bias.Slide32
What happens at higher redshift?
If very massive BHs are associated with very massive DM halos, then high-redshift quasars should sit in very rare, many
peaks in the density
field.
So
we expect high-redshift quasars to be
more
strongly
clustered.
Shen
et al. 2007
For 2.9 <
z
< 3.5:
r
0
=16.9±1.7
Mpc/h
;
b~10
For
z
> 3.5:
r
0
=24.3±2.4
b~15Slide33
Use ellipsoidal collapse model (
Sheth
, Mo &
Tormen
,
2001)
to turn estimates of
b
Q
into mass of halos hosting UVX quasars.
Find very little evolution in halo mass with redshift.
Our mean halo mass of ~5x10
12
h
-1
M
Solar
is halfway between characteristic masses from
Croom
et al. (
2005)
and
Porciani
et al. (
2004).
This is comparable to the mass of galaxy groups, supporting the idea that quasars are triggered by mergers.Slide34
Hierarchical Halo Merging
Lacey & Cole (1993)Typical quasar hosts double in mass every Gyr or soConstancy of quasar host halo mass thus limits quasar lifetime to around 106.5
to 10
7.5
yrs
Time
Mass
Time for 2x Mass
CDM theory tells us the expected space density of halos. Comparing with the observed quasar density allows us to determine the fraction of time a quasar is shining. Slide35
Clustering’s Luminosity Dependence
Quasars accreting over a wide range of luminosity are driven by a narrow range of black hole masses
M-
relation mean a wide range of quasar luminosities will then occupy a narrow range of M
DMH
Lidz
et al. 2006
old model
new modelSlide36
No L Dependence for Quasars
Zehavi et al. 2005galaxies
Shen
et al. 2007
quasarsSlide37
What Next?
Hopkins et al. 2007
Measuring bias of faint high-
z
quasars will break
degeneracies
between feedback models.
bright quasars (e.g., SDSS)
faint quasars (e.g., LSST)
Richards et al. 2006Slide38
What We (Used To) Expect
Galaxies (and their DM halos) grow through hierarchical mergersQuasars inhabit rarer high-density peaksIf quasars long lived, their BHs
grow with cosmic time
M
BH
-σ relation implies that the most luminous quasars are in the most massive halos.
More luminous quasars should be more strongly clustered (
b/c
sample higher mass peaks).
QLF from
wide
range of BH masses (DMH masses) and
narrow range of accretion rates.
Slide39
What We Get
Galaxies (and their DM halos) grow through hierarchical mergersSomething causes the growth of galaxies and their BHs to terminate even as DM halos continue to growQuasars always turn on in potential wells of a certain size (at earlier times these correspond to relatively higher density peaks).
Quasars turn off on timescales shorter than hierarchical merger times, are always seen in similar mass halos (on average).
M
BH
-σ relation then implies that quasars trace similar mass black holes (on average)
Thus little luminosity dependence to quasar clustering (L depends on accretion rate more than mass).
Need a wide range of accretion
rates
for a narrow range of MBH to be consistent with QLF.Slide40
Correlation length insensitive to:
Quasar colorVirial black hole mass (as measured from spectrum)Redshift (at least to z~2.5)Luminosity (except for most luminous 10%)
Clustering is a measure of dark matter halo mass. None of these quantities correlate strongly enough with halo mass to have a measurable effect.
This suggests that luminosity is not closely tied to black hole
mass (at least to z~2.5). Slide41
What Does Evolution in Bias Mean?
Quasars at high redshift “turned on” in environments which are now clustered far more than typical galaxy environments.We don’t see them in these environments nearer the present day. They’ve “turned off”.Can use Press-Schecter formalism to turn quasar bias into mass of host halos…Slide42
Quasars and Cosmology
January 22nd, 2008, UIUCWhat the observations tell us about quasars as a cosmological population
Quasar lifetimes ~10
7
years. Very short. Several 100 quasar lifetimes between z=2 and z=1.
Quasars occupy similar mass host halos (M
DMH
) at every redshift (z < 3).
Quasars accrete at a wide range of luminosities for a narrow range of black hole masses (M
BH
).Slide43
Luminosity-Dependent Density Evolution
Ueda et al. (2003)
AKA:
Comsic DownsizingSlide44
A quasar is a galaxySlide45
A quasar is a galaxy
in which accretion onto a supermassive black hole produces copious amounts of non-stellar radiation over the entire electromagnetic spectrum; this light dwarfs the light from the galaxy itself.
L ~ 10
43-46
ergs/s
M ~ 10
6-9
M
sun
Quasar = active galactic nuclei = AGN = Seyfert etc.Slide46
H+05 ApJ,630, 716
“In our interpretation, the bright and faint ends of the LF correspond statistically to similar mixes of galaxies, but in various stages of evolution. However, in all other competing scenarios, the QLF is directly related to the mass of the host galaxy. Therefore, an observational probe that differentiates quasars based on their host galaxy properties such as, for example, the dependence of clustering of quasars on luminosity, can be used to discriminate our picture from older models.”Slide47
Comparing Probability Densities
100,000 z<3 quasars in DR1 (95% efficient to g=21)SDSS is 85% efficient to g=191,000,000 quasars from 0<z<5 in the whole SDSS area.
Richards et al. 2004cSlide48
The MBH-sigma Relation
(Tremaine et al. 2002; also Ferrarese & Merritt 2000; Gebhardt et al. 2000; Magorrian et al. 1998)
Massive black holes
co-evolve
with their host galaxies.Slide49
LSST
LSST corp.Slide50
What is the Luminosity Dependence of the Clustering?
Shen
et al. 2009: The most luminous 10% of quasars are more strongly clustered. Correlation length of 9.5 vs. 7 h
-1
Mpc, difference significant at 2.5
.Slide51
We quantify clustering via the correlation function (
r) The excess fractional probability of finding a galaxy a distance r from a given galaxy: dN = n dV (1 + (r))
The correlation function is often fit to a power-law form:
(
r) = (r/r
0
)
-
For nearby galaxies, the
correlation length
r0 is about 5 h
-1
Megaparsecs, and
=
-1.8.Slide52
DR5 quasar sample, a complete sample of ~30,000 objects. Projected correlation function in redshift slices.
Ross et al. 2009
The clustering length changes very little with redshift. Slide53
Quasar Luminosity Function
Quasars peaked around a redshift of 2.5
e.g., Richards et al. 2006Slide54
Hopkins et al. 2005
Most QLF models assume they are either “on” or “off” and that there is a mass/luminosity heirarchy.Hopkins et al.: quasar phase is episodic and “all quasars are created equal” (with regard to mass/luminosity).Slide55
The SDSS QLF
SDSS, though relatively shallow, allows us to determine the QLF from z=0 to z=5 with a single dataset.
Richards et al. (2006)
QLF slope flattens at high-z.
Not PDE, PLESlide56
Understanding the High-z QLF
The change of the bright slope in the QLF at high redshift means the distribution of intrinsic luminosities is broader at high redshift.
Hopkins et al. 2005
Richards et al. 2006Slide57
QLF ComparisonSlide58
For
CDM
cosmology, quasar bias evolves as a function of redshift (Significance of detection of evolution >99.5% using only DR4 KDE data set).
Detection in good agreement with earlier results from independent spectroscopic data (2dF QSO redshift survey).Slide59
Luminosity EvolutionVery little dependence of quasar clustering on absolute magnitude of the quasar population (Myers et al. 2007) using large SDSS photometric sample
bias
M
gSlide60
Luminosity Evolution
Similarly from the SDSS+2dF=2SLAQ quasar survey.
da Angela et al. 2008Slide61
Comoving correlation length (h
-1 Mpc)
Hopkins et al. 2007: Predicted correlation length with redshift; details depend
on magnitude limit and model for feedback. Probing to fainter magnitudes at high redshift is important!
i=20.2
i=19Slide62
X-ray Surveys
Hasinger et al. 2005
X-ray surveys probe much deeper and are more complete, but cover tiny areas.Slide63
MIR Colors
e.g., Stern et al. 2005
Richards et al. 2009b
Redshift
MIR colors have similar problems at 3.5<
z
<5.Slide64
Optimizing Quasar Surveys
X-ray/IR surveys are deep enough (up to a few 1000 AGN/sq. deg.), but not wide enough.Optical surveys are wide enough, but not deep enough.
SDSS
Need deeper optical surveys and/or larger area X-ray/IR surveys.
.Slide65
Hickox SlideSlide66
Quasar Evolution
The intrinsic properties of quasars have changed relatively little over cosmic time.Fan et al. 2004, 2008
Vignali
et al. 2005;
Shemmer
et al. 2005
NV
OI
SiIV
Ly a
Ly a forest
z~6 composite
Low-z compositeSlide67
The Rise of Quasars at z~6
z~6 quasars constrain formation models due to their large masses and short ages.
e.g., Richards et al. 2006Slide68
Eddington Luminosity/Mass
If the luminosity of a quasar is high enough, then radiation pressure from electron scattering will prevent further gravitational infall.
L
E
= 1.38x10
38
M/
M
sun
erg/
s
M
E
= 8x10
7
L
46
M
sun
Sets an upper limit to the luminosity for a given mass, or
equivalently
a minimum mass for a given luminosity.