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 the Shape of Quasar LF

Richards 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?

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

(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

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

Spitzer

ALMA

Dust torus

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 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?

Question

• Should one be surprised about the existence of luminous, high-mass, high metallicity quasars at the end of reionization?