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, Diamond-Stanic, et al.
The Highest Redshift Quasars Today
• 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
• 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
wavelength4000 A 9000 A
reds
hift
0
1
2
3
5
Ly
CIV
CIIIMgII
HOIII
FeII
FeII
Ly forest
Evolution of quasar densities
Exponential decline of quasar density at high redshift, different from normal galaxies, mostly luminosity dependent
Richards et al. 2005,Fan e al. 2005
SFR of galaxies
Density of quasars
Bouwens et al.
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• The largest halo in Millennium
simulation (500 Mpc cube) at z=6.2– 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
z=6.2
z=0
Dark matter galaxy
Springel et al. 2005
Early Growth of Supermassive Black Holes
Vestergaard 2004 Dietrich and Hamann 2004
• Billion solar mass BH at z~6 indicates very early growth of BHs in the Universe
Formation timescale (assuming Eddington)
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
Evolution of X-ray AGN LF
-- downsizing
• At high-luminosity: X-ray and optical traces the same population
• How does optically-selected quasar population evolve at low-luminosity?
Hasinger et al. 2005
Evolution of Quasar LF Shape
• 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?
Richards, et al.; Fan et al. 2005
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
Jiang et al. in prep.
• 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?
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
(low-z)
(high-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 high-redshift
• Another hint of quasars at z>3 being somewhat different from low-z quasars? Fan et al. in preparation
Wyithe and Loeb 2004
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)
izJ composite (z_lim =26)
Pentericci et al.
quasar
NV
OI SiIV
Ly a
Ly a forest
• Rapid chemical enrichment in quasar vicinity• Quasar env has supersolar metallicity -- metal lines, CO,
dust etc.• High-z quasars and their environments mature
early on
The Lack of Evolution in Quasar Intrinsic Spectral Properties
Chemical Enrichment at z>>6?
• 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?
Fan et al. 2001Barth et al. 2003
Early enrichment of quasars
Venkatesan et al. 2004
• 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 under-produce N/C
– “normal” stars existed at very high-z in quasar environment.
Top-heavy IMF
Normal IMFPopIII
z~6 Quasar SEDs: from X-ray to radio
• 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…
dust
Mid-IR SEDs of z~6 Quasars
• Overall shape shows little evolution• But obj-obj variation significant
– z=6.42 quasar: stronger dust emission with higher T?
Min. from dust sublimation
BH mass distribution
McLure et al. SDSS DR 1
Fan et al. >1000 quasars at z>3
CIV Upper Limit?
How fast can the most massive high-z BH grow? Will it be stopped by negative feedback?
L~M
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.
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 Observationof High-z Quasars
• 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
500 – 2000 Msun/year Quasars are likely sites of intensive star formation• FIR luminosity not correlated with UV luminosity of quasar
Arp 220
Bertoldi et al. 2003
PSS J2322+1944 (z=4.12)
• CO Einstein ring– Modeled by star-
forming 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?
caution: selection effect whenusing luminous quasars
Walter et al. 2004
1 kpc
VLA CO 3—2 map
60 km/s
Channel Maps
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?