Post on 15-Jan-2016
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