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The Most Distant Quasars:Probing the End of Cosmic Dark Ages
Xiaohui FanSteward Observatory
The University of Arizona
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The SDSS Collaboration
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The Most Distant Quasars:Probing the End of Cosmic Dark Ages
Xiaohui FanSteward Observatory
The University of Arizona
![Page 4: The Most Distant Quasars: Probing the End of Cosmic Dark Ages Xiaohui Fan Steward Observatory The University of Arizona.](https://reader035.fdocuments.us/reader035/viewer/2022062804/56649cec5503460f949b8a41/html5/thumbnails/4.jpg)
40 Years Ago:First Quasar: 3C 273 by Maarten Schmidt
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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
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Exploring the Edge of the Universe
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SDSS at Your Service
Courtesy of Arizona graduate students
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The HighestRedshift Quasars Today
• z>4: ~700 known • z>5: ~30 • z>6: 6• Highest redshift:
z=6.42
SDSS DiscoveriesTotal Discoveries
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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.
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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.
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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
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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
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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.
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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
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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
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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
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The Lack of Evolution in Quasar Intrinsic Spectral Properties
NVOI SiIV
Ly a
Ly a forest
Fan et al. 2004
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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
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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.
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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
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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
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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
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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
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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
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Gnedin 2000
Neutral fraction
UV background
Gas density
Gas temperature
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The end of dark ages: Movie
Courtesy of N. Gnedin
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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
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VLT/FOS2
Pentericci et al. 2002
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Keck/ESI 30min exposure
Gunn-Peterson Trough in z=6.28 Quasar
Keck/ESI 10 hour exposure
White et al. 2003
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Gunn-Peterson troughs confirmed by new z>6 quasars
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Strong Evolution ofGunn-Peterson Optical Depth
Fan et al. 2004
Transition at z~5.7?
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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
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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
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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
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Comparing with Models
postoverlapoverlapping
epochPre-
overlap Volume-averageed
Mass-averaged
Fan et al. 2002
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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
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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
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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