The Most Distant Quasars:Probing the End of Cosmic Dark Ages

Xiaohui FanSteward Observatory

The University of Arizona

The SDSS Collaboration

The Most Distant Quasars:Probing the End of Cosmic Dark Ages

Xiaohui FanSteward Observatory

The University of Arizona

40 Years Ago:First Quasar: 3C 273 by Maarten Schmidt

Quasars as Cosmology Probes

• The Study of Highest-Redshift Quasars Probes:– The epoch of first generation of galaxies/quasars

– Models of black hole formation

– Role of quasar/BH activity in galaxy evolution

– State of intergalactic medium

– Ionizing background at high-z

– History of reionization probing the end of cosmic dark ages

Exploring the Edge of the Universe

SDSS at Your Service

Courtesy of Arizona graduate students

The HighestRedshift Quasars Today

• z>4: ~700 known • z>5: ~30 • z>6: 6• Highest redshift:

z=6.42

SDSS DiscoveriesTotal Discoveries

Outline

• SDSS Quasar Survey• Search for the First Quasars• Co-formation of First Quasars and Galaxies• Lyman Absorption of z~6 quasars

– Discovery of complete Gunn-Peterson troughs

– Implication on the epoch of reionization

• Collaborators: Strauss, Schneider, Becker, White, Richards, Penterricci, Rix, Narayanan, Hennawi, Carilli, Bertoldi, Walter, Cox, Lo et al.

SDSS Overview

• Primary Telescope: 2.5m wide-field (2.5 deg)

• Imaging Survey (wide-field 54 CCD imager)– Main Survey: 10000 deg2

– Five bands, 3000 – 10000 Å

– rlim ~ 22.5, zlim ~ 20.5

• Spectroscopic Survey– 106 galaxies (r<17.8)

– 105 quasars ( 0 < z < 6.5)

– Interesting stars, radio/x-ray sources etc.

SDSS Quasar Survey

• Color selected, flux-limited sample of 100,000 quasars over 10,000 deg²

• Fully automated pipeline selection up to z~5.5

• z band (9000 Å) allows detection of quasars up to redshift of 6.5

• Progress: ~50,000 quasars discovered from SDSS data

Stellar locus

quasar

Z=3Z=4

Z=5

Richards, Fan, Newberg, Strauss, et al. 2002

17,000 Quasars from the SDSS Data Release One

wavelength4000 A 9000 A

reds

hift

0

1

2

3

5Ly a

CIV

CIII

MgII

HaOIII

Search for the First Quasars

• Color selection of i-drop out quasars

– At z>5.5, Lyα enters z-band quasars have only red i-z measurement

– faint objects: z-band only detections

• Technical Challenges:– Rarest objects

• One z~6 quasar every 500 deg2

• Needles in a haystack

one among 10 million objects and 5 million cosmic rays

• Key: contaminant elimination

– Reliability of faint z photometry follow-up high S/N z photometry

– Major contaminants are L and T type Brown Dwarfs additional IR photometry

Fan, Narayanan, Lupton, Strauss et al.

Search for the First Quasars

• Separating z~6 quasars and BDs– Follow-up IR

photometry

– For quasar: z-J ~ 1

– For late-L to T:

z-J > 2

Fan, Narayanan, Lutpon, Strauss et al.

Z>5.7 quasar

Find the most distant quasars:needles in a haystack

2..Photometric pre-selection: ~500 objects

1. SDSS database: 100 million objects

APO 3.5m

Calar Alto (Spain)3.5m

3. Photometric and spectroscopicIdentification (~50 objects)

4. Detailed spectra(12 new quasars at z~6)

Keck 10m

Hobby-Eberly 9.2mKitt Peak 4m

MMT 6.5m

z~6 Quasars

• SDSS i-dropout Survey:– By Dec 2003: 5000 deg2 at zAB<20

– Twelve luminous quasars at z>5.7

– By product: > 30 T dwarfs and large number of L dwarfs

• 20 – 40 at z~6 expected in the whole survey

The Lack of Evolution in Quasar Intrinsic Spectral Properties

NVOI SiIV

Ly a

Ly a forest

Fan et al. 2004

Chemical Enrichment at z>>6?

• Strong metal emission consistent with supersolar metallicity• NV emission multiple generation of star formation• Fe II emission might be from metal-free Pop III • Question: what can we learn about star formation and chemical enrichment

from abundance analysis of these most extreme environment in the early universe?

Fan et al. 2001Barth et al. 2003

Quasar Density at z~6• Based on nine z>5.7 quasars:

– Density declines by a factor of ~20 from z~3

– Number density implies that quasars are unlikely to provide enough UV background earliest galaxes ionized the universe!

• Cosmological implication– MBH~109-10 Msun

– Mhalo ~ 1013 Msun

– How to form such massive galaxies and assemble such massive BHs in less than 1Gyr??

• The rarest and most biased systems at early times

• Using Eddington argument, the initial assembly of the system must start at z>>10

co-formation and co-evolution of the earliest SBH and galaxies

Fan et al. in prep.

Sub-mm and Radio Observationof High-z Quasars

• Probing dust and star formation in the high-z quasar host galaxies• Using IRAM and SCUBA: ~40% of radio-quite quasars at z>4 detected at 1mm (observed frame) at

1mJy level• Combination of cm and submm submm radiation in radio-quiet quasars come from thermal

dust with mass ~ 108 Msun

• If dust heating came from starburst star forming rate of

500 – 2000 Msun/year Quasars are likely sites of intensive star formation

Arp 220

Bertoldi et al. 2003

Submm and CO detection in the highest-redshift quasar: • Dust mass: 108 – 109Msun • H2 mass: 1010Msun • Star forming rate: 103/yr co-formation of SBH and

young galaxies

Co-evolution of early galaxies and supermassive BHs

• Presence of 109-10 solar mass BH at z>6 it has to begin the assemble at z>10

• High metallicity in the quasar environment recent star formation and chemical enrichment

• Presence of heated dust (submm) and gas possible on-going star formation with rate of ~1000 solar mass/year

The initial assembly of SBH coeval with the initial assemble of host galaxy

• Spitzer and ALMA Probing the BH/galaxy formation connection

Searching for Gunn-Peterson Trough

• Gunn and Peterson (1965)– “It is observed that the continuum of the source

continues to the blue of Ly-α ( in quasar 3C9, z=2.01)”

– “only about one part of 5x106 of the total mass at that time could have been in the form of intergalactic neutral hydrogen ”

• Absence of G-P trough the universe is still highly ionized

A brief cosmic historyrecombination

Cosmic Dark Ages: no light no star, no quasar; IGM: HI

First light: the first galaxies and quasars in the universeEpoch of reionization: radiation from the first object lit up and ionize

IGM : HI HII reionization completed, the universe is transparent and the dark ages ended

todayCourtesy: G. Djorgovski

Gnedin 2000

Neutral fraction

UV background

Gas density

Gas temperature

The end of dark ages: Movie

Courtesy of N. Gnedin

Increasing Lyα absorptionwith redshift: zabs fobs/fcon

---------------------------

~5.5 0.10 ~5.7 0.05 ~6.0 <0.002

Zero flux over 300Å immediately blueward of Lyα emission in z=6.28 quasar Detection of complete Gunn-Peterson Trough: τ>>1 over large region of IGM Becker et al. 2001

VLT/FOS2

Pentericci et al. 2002

Keck/ESI 30min exposure

Gunn-Peterson Trough in z=6.28 Quasar

Keck/ESI 10 hour exposure

White et al. 2003

Gunn-Peterson troughs confirmed by new z>6 quasars

Strong Evolution ofGunn-Peterson Optical Depth

Fan et al. 2004

Transition at z~5.7?

Implications of Complete Gunn-Peterson Trough

• G-P optical depth at z~6:

– Small neutral fraction needed for complete G-P trough

– By itself not indication that the object is beyond the reionization epoch

• For uniform IGM:

– Measurement of optical depth can be used to constrain ionizing background

• IGM is highly non-uniform– regions with different density have different Lyα transmission– to constrain ionization state: have to take into account the density

distributions of the IGM

)/(10GP

5~ HHI nn

)()()1(225.4

~ Thzb

Evolution of Ionizing Background

• Ionizing background estimated by comparing with cosmological simulations of Lyman absorption in a LCDM model– Stronger constraint from the

Lyβ and Lyγ Gunn-Peterson trough

– Ionizing background declines by a factor of >25 from z~3 to z~6

– Indication of a sudden change at z~6?

Fan et al. in prep

Photoionizing rate

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%

– Gunn-Peterson test only sensitive to small neutral fraction and saturates at large neutral fraction

• At z~6: – Last remaining neutral regions

are being ionized

– The universe is >1% neutral

– Marks the end of reionization epoch??

Fan et al. in prep

mass ave.

vol. ave

Comparing with Models

postoverlapoverlapping

epochPre-

overlap Volume-averageed

Mass-averaged

Fan et al. 2002

The end of dark ages

• G-P test shows: at z~6, the IGM is about 1% neutral the tail end of the reionization process

• Discovery of G-P troughs in the four highest redshift quasars known end of reionization at z~6 with small dispersion among different lines of sight

• CMB polarization shows: substantial ionization by z~17:

• Combining GP with CMB reionization history:

– Reionization last from 20 to 6? (600 million years) ?

– Reionization is not a phase transition

– Reionization seems to be more complicated by the simplest theory

What’s next?

• More quasars: understanding the topology of the reionization from multiple lines of sights

• Evolution of heave element: chemical enrichment and feedback from the first galaxies

• Pushing towards higher redshifts: IR surveys, JWST finding the first light

• More sensitive to large neutral fraction– GRBs? 21cm?

– Detailed comparison with CMB polarization

Mapping the reionization history and the end of the cosmic dark ages

Summary

• High-redshift quasars evolve strongly with redshift:– Density declines by ~20 from z~3 to z~6– Evolution much faster than normal galaxies

• High-redshift quasars are sites of spectacular star formation:– Sub-mm and CO detections high star formation rate– Possible supersolar metallicity at z>6 in quasar environment

• High-redshift quasars probe the end of reionization epoch:– Lyα absorption increases dramatically at z>5.7 – Consistent detections of complete Gunn-Peterson troughs in the

highest-redshift objects – At z~6: ionizing background much lower, neutral fraction >1%,

moderately overdense regions still neutral

it marks the end of the reionization epoch when the last remaining HI in the IGM is being ionized

combining with CMB results: revealing the reionization history and the end of cosmic dark ages