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Evolution of High-Redshift Quasars
Xiaohui Fan
University of Arizona
Castel Gandolfo, Oct 2005
Collaborators:Strauss,Schneider,Richards,
Hennawi,Gunn,Becker,White,Rix,Pentericci,
Walter, Carilli,Cox,Bertoldi,Omont,Brandt,
Vestergaard,Eisenstein, Cool, Jiang, DiamondStanic, et al.
The Highest Redshift Quasars Today
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z>4: >1000 known
z>5: >60
z>6: 9
SDSS i-dropout Survey:
– By Spring 2005: 6600 deg2 at
zAB<20
– Nineteen luminous quasars at
z>5.7
• Complete sample for bright
quasars at z~6:
– ~8000 deg, ~25 quasars by
2006
• Next: work on faint sample at
z~6
Outline
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Evolution of luminosity function
BH masses at high-z
High-z quasar clustering and environment
Evolution of quasar spectra and metallicity
Dust and star formation in high-z quasar host
galaxies
46,420 Quasars from the SDSS Data Release Three
5
Ly forest
3
Ly
2
redshift
CIV
CIII
MgII
FeII
1
FeII
OIII
H
0
4000 A
wavelength
9000 A
Evolution of quasar densities
Density of quasars
SFR of galaxies
Bouwens et al.
Exponential decline of quasar
density at high redshift, different
from normal galaxies, mostly
luminosity dependent
Richards et al. 2005,
Fan e al. 2005
Quasar Density at z~6
• From SDSS i-dropout
survey
– Density declines by a factor of
~40 from between z~2.5 and
z~6
• Cosmological implication
– MBH~109-10 Msun
– Mhalo ~ 1012-13 Msun
– rare, 5-6 sigma peaks at z~6
(density of 1 per Gpc3)
• Assembly of massive
dark matter halo
environment?
• Assembly of
supermassive BHs?
Fan et al. 2004
Simulating z~6 Quasars
Dark matter
galaxy
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The largest halo in Millennium
simulation (500 Mpc cube) at z=6.2
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–
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z=6.2
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–
z=0
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Springel et al. 2005
Virial mass 5x1012 M_sun
Stellar mass 5x1010 M_sun
SFR: 300 M_sun/year
Resembles properties of SDSS quasars
Even the largest N-body simulation
not big enough to produce one SDSS
z~6 quasar…
Today: 1.5 x 1015 M_sun cluster
Much massive halos existed at z~6,
but..
How to assemble such mass BHs and
their host galaxies in less than 1Gyr??
– The universe was ~20 tedd old
– Initial assembly from seed BH at
z>>10
– Little or no feedback to stop
BH/galaxy growth
Early Growth of Supermassive Black
Holes
Formation timescale (assuming Eddington)
Vestergaard 2004
Dietrich and Hamann 2004
Lack of spectral evolution in high-redshift quasars  quasar BH estimate valid at high-z
BH mass estimate: using emission line width to approximate gravitational velocity, accurate
to a factor of 3 – 5 locally
• Billion solar mass BH at z~6 indicates very early
growth of BHs in the Universe
Evolution of X-ray AGN LF
-- downsizing
Hasinger et al. 2005
• At high-luminosity: X-ray and optical traces the same
population
• How does optically-selected quasar population evolve at
low-luminosity?
Evolution of the Shape of Quasar LF
Richards et al. 2005
Evolution of Quasar LF Shape
Richards, et al.; Fan et al. 2005
• High-z quasar LF different from low-z
– Bright-end slope of QLF is a strong function of redshift
– Transition at z~3 (where quasar density peaks in the
universe)
– Different formation mechanism at low and high-z?
Probing the Evolution of Faint
Quasar
• SDSS Southern Deep Spectroscopic Survey
– 270 deg along Fall Equator in the Southern Galactic
Cap
– Down to ~25 mag in SDSS bands with repeated
imaging
– Spectroscopic follow-up using 300-fiber Hectospec
spectrograph on 6.5-meter MMT
– Reaches AGN luminosity at z~2.5
– Few hundred faint quasars at z>3
– 10 – 20 at z~6
Evolution of faint quasars in SDSS Deep Survey
• Sample reaches AGN
luminosity at z~3
• Strong evolution in LF shape
• Simple luminosity evolution
clearly not a good description
• “break” luminosity evolves:
-- downsizing
• faint end slope also evolve:
-- steeper at high-z?
Jiang et al. in prep.
Downsizing of optical quasars
High-z QLF from SDSS Deep Stripe Survey
• High-z quasar LF
different from low-z
– High-z LF much flatter
– Implies that more
luminous quasars grow
early in the Universe
• Similar to the early
growth of massive
galaxies??
– Quasars are not major
contributors to
reionization at z>6
z ~ 4.5
(high-z)
(low-z)
Fan et al. 2005
Clustering of Quasars
• What does quasar
clustering tell us?
– Bias factor of quasars
 average DM halo
mass
– Clustering provides the
most effective probe to
the statistical properties
of quasar host DM
properties at highredshift
• Another hint of quasars
at z>3 being somewhat
different from low-z
quasars?
Wyithe and Loeb 2004
Fan et al. in preparation
Environment of a z=6.3
quasar
• Deep VLT i-z-J imaging
• 19 i-dropout candidates
in 38 sq. arcmin at z<25.6
• >6 times higher than in
GOODS etc.
(also Stiavelle et al. 2005)
quasar
izJ composite (z_lim =26)
Pentericci et al.
The Lack of Evolution in
Quasar Intrinsic Spectral Properties
Ly a
NV
Ly a forest
OI
SiIV
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Rapid chemical enrichment in quasar vicinity
Quasar env has supersolar metallicity -- metal lines, CO, dust
etc.
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High-z quasars and their environments mature early on
Chemical Enrichment at z>>6?
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Strong metal emission  consistent with supersolar metallicity
NV emission  multiple generation of star formation from enriched pops
Fe II emission  type II SNe… some could be Pop III?
Question: can we generalize the conclusion drawn from regions around
central BHs to the whole early Universe?
Barth et al. 2003
Fan et al. 2001
Early enrichment of quasars
Top-heavy IMF
Normal IMF
PopIII
• Metallicity in BLR of z~6
quasars: 1 -- 10 solar
• Nuclear synthesis model
shows:
– Normal IMF is sufficient
(given high SFR)
– Type Ia is not critical in Fe
production
– Mostly Pop III underproduce N/C
– “normal” stars existed at
very high-z in quasar
environment.
Venkatesan et al. 2004
z~6 Quasar SEDs: from X-ray to radio
dust
• Lack of evolution in UV, emission line and X-ray  disk and emission
line regions form in very short time scale
old quasars in a young universe…
• But how about dust? Timescale problem: running out of time for AGB
dust… Spitzer…
Mid-IR SEDs of z~6 Quasars
Min. from dust sublimation
• Overall shape shows little evolution
• But obj-obj variation significant
– z=6.42 quasar: stronger dust emission with higher T?
BH mass distribution
CIV
 Upper Limit?
L~M
Fan et al. >1000 quasars at z>3
McLure et al. SDSS DR 1
How fast can the most massive high-z BH grow?
Will it be stopped by negative feedback?
BH Accretion Rate
z>3
z<3
Evolution of Quasar BH Mass Function
• Lack of spectral evolution:
– Similar BLR structure
– BH mass scaling relation at low-z
still valid at high-z
• Quasar mass function: represents
accretion history traced by luminous
quasars
• Not surprisingly, closely follows
evolution of luminosity function:
– Flatter MF at high-z
– Probing evolution of accretion rate?
– At z>2: MF shape similar and flat at
high-mass end, but the shape
different at low-z
Vestergaard et al.
Probing the Host Galaxy Assembly
 Dust torus
Spitzer
ALMA
Cool Dust in
host galaxy
Sub-mm and Radio Observation
of High-z Quasars
• Probing dust and star formation in the most
massive high-z systems
• Advantage:
– No host galaxy contamination
– Negative K-correction for both continuum and line
luminosity at high-z
– Give direction measurement to
• Star formation rate
• Gas morphology
• Gas kinematics
Sub-mm and Radio Observation
of High-z Quasars
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Using IRAM and SCUBA: ~30% of radio-quiet quasars at z>4 detected at
1mm (observed frame) at 1mJy level
 submm radiation in
radio-quiet quasars
come from thermal
dust with mass ~ 108 Msun
• If dust heating came from starburst
 star formation rate of
Arp 220
500 – 2000 Msun/year
Quasars are likely sites
of intensive star formation
• FIR luminosity not correlated
with UV luminosity of quasar
Bertoldi et al. 2003
PSS J2322+1944 (z=4.12)
• CO Einstein ring
– Modeled by starforming disk with
2kpc radius
– CO line-width
280km/s
– BH Mass ~10^9 solar
– Star formation rate
900 solar mass/year
• 15 detections of CO
at z>2 (5/6 known
CO sources at z>4
are quasars)
Carilli et al. 2003
Submm, CO and CII detection
in the highest-redshift quasar
• Dust mass: 108 – 109Msun
• H2 mass: 1010Msun
• Star formation rate: 103/yr
 co-formation of SBH and
young galaxies
Mailino et al. 2005
High-resolution CO
Observation of z=6.42 Quasar
• Spatial Distribution
– Radius ~ 2 kpc
– Two peaks separated by 1.7 kpc
• Velocity Distribution
– CO line width of 280 km/s
– Dynamical mass within central 2 kpc: ~ 1010
M_sun
– Total bulge mass ~ 1011 M_sun
< M-sigma prediction
• BH formed before
complete galaxy assembly?
Channel Maps
caution: selection effect when
using luminous quasars
60 km/s
VLA CO 3—2 map
1 kpc
Walter et al. 2004
High-z vs. Low-z Quasars
• LF evolution:
– Strong evolution in total density
– Downsizing of characteristic luminosity
– At z>3:
• Declining density
• Flatter LF/MF
• Stronger clustering
– Are high-z and low-z quasars different?
• Spectral evolution:
– Little or no evolution in continuum/emission line properties
– Dust properties might have changed
– High-metallicity requires presence of evolved stellar pop at high-z
– How does this constrain host evolution?
• BH/galaxy co-evolution
– Billion solar-mass BH at the end of reionization
– Strong star-formation associated with BH growth
– Has M-sigma relation established at high-z?
Question
• Should one be surprised about the existence of
luminous, high-mass, high metallicity quasars at
the end of reionization?