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The Highest-Redshift Quasars and the End of Cosmic Dark Ages

The Highest-Redshift Quasars and the End of Cosmic Dark Ages. Xiaohui Fan Collaborators: Strauss,Schneider,Richards, Hennawi,Gunn,Becker,White,Rix,Pentericci, Walter, Carilli,Cox,Bertoldi,Omont,Brandt, Vestergaard, Jiang, Diamond-Stanic, et al. SDSS collaboration. End of cosmic dark ages.

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The Highest-Redshift Quasars and the End of Cosmic Dark Ages

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  1. The Highest-Redshift Quasars andthe End of Cosmic Dark Ages Xiaohui Fan Collaborators:Strauss,Schneider,Richards, Hennawi,Gunn,Becker,White,Rix,Pentericci, Walter, Carilli,Cox,Bertoldi,Omont,Brandt, Vestergaard, Jiang, Diamond-Stanic, et al. SDSS collaboration

  2. End of cosmic dark ages • Hot Big Bang • Cosmic Dark Ages: no light no star, no quasar, universe dark; IGM atomic (neutral) and opaque to UV • First light: the first galaxies and quasars in the universe • End of cosmic dark ages: Universe lit up and heated up Dark --> light Neutral --> ionized (reionization)  today Courtesy: G. Djorgovski

  3. Existence of supermassive black holes (BHs) at the end of cosmic dark ages BH accretion history in the Universe? Relation of BH growth and galaxy evolution Why Distant Quasars? molecular CO emission from z=6.42 quasar • Probing the cosmic reionization Evolution of Quasar Density Detection of Gunn-Peterson Trough

  4. How to find the earliest and most distant quasars? • They are extremely rare • One per 500 sq. deg at z>6 (M<-27) • Require the largest survey of the sky to catch them • Search for “red”, i-dropout objects in the Sloan Digital Sky Survey • They are faint at high-redshift • Require deep follow-up spectroscopic observations • SDSS i-dropout survey: • Candidate selection from SDSS • Fellow-up observations mainly on four work-horse telescopes: APO 3.5m; KPNO 4-m; MMT; Keck

  5. The Highest Redshift Quasars and Galaxies • SDSS i-dropout Survey: • Completed in June 2006: 7600 deg2 at zAB<20 • Twenty-five luminous quasars at z>5.7 • zmax=6.42 • Cosmic age ~ 800 Myr • The first 6-7% of cosmic history • Dropout and Ly emission galaxies • zspec < 6.6 • zphot ~ 7 - 8 • GRBs • 050904 z=6.30

  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? Massive black holes in early universe Fan et al. 2004

  7. How fast can a black hole grow? • Quasars shine by converting potential energy to radiative energy when accreting gas: • Radiative efficiency of ~10% • Quasar maximum accretion rate is limited by the presence of radiation pressure (Eddington limit) • At maximum accretion, e-folding timescale of quasar growth is ~40 million years • Earliest quasars likely grew from “seed” black holes resulted from stellar collapse • Seed mass ~10 - 100 M_sun • To grow a billion solar mass BH needs about 20 e-folding time -> ~ 800 million years, non-stop • The age of the universe at z~6 is ~800 million years • Barely enough time for quasars to grow, even non-stop from the big bang???

  8. Surprise 1… • How did black holes grow so quickly in the first billion years of the cosmic history? • New (astro)physical processes? • Direct formation of intermediate mass BH? • Much more efficient accretion? • How are the earliest quasars related to the earliest galaxies?

  9. The Lack of Evolution in Quasar Intrinsic Spectral Properties Ly a NV Ly a forest OI SiIV • Rapid chemical enrichment in quasar vicinity • High-z quasars and their environments mature early on

  10. Submm and CO observation of z=6.42 quasar:Co-formation of earliest BH and galaxies • Strong submm source: • Dust T: 50K • Dust mass: 7x108 Msun • Star-formation rate of ~2000 M/yr • Strong CO source • Tkin ~ 100K • Gas mass: 2x1010 Msun • gas, dust properties similar to those of the brightest local starburst galaxies Bertoldi et al.

  11. High-resolution CO Observation of z=6.42 Quasar VLA CO 3—2 map • 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 Small, star-forming galaxy hosted over-sized BH • BH formed before complete galaxy assembly? 1 kpc Walter et al. 2004 Channel Maps  60 km/s 

  12. Lineless quasars: radio quiet BL Lac or quasars with no BLR? • No emission line, radio-quiet quasars at z>4 • ~1% of high-z quasars • No obvious low-z counterparts • No BL Lac signature • A separate population of quasars? Ly  distribution Lineless Quasars: EW(Ly)<10 Log EW (Ly ) Diamond-Stanic et al. 2006 Fan et al. 2006

  13. Surprise II… • The spectra of these earliest quasars look almost identical to those in the local universe • No evolution in spectral properties? • Mature quasars in a very young universe? • Black holes grew earlier in the universe?

  14. reionization Gunn-Peterson (1965) effect deep HI absorption in high-z quasar spectrum prior to the end of reionization

  15. First detection of Gunn-Peterson Effect

  16. The Universe transforming from opaque to transparent at the end of cosmic dark ages transparent opaque

  17. Optical depth evolution accelerated z<5.7:  ~ (1+z)4.5 z>5.7:  ~ (1+z)>11 The End of Reionization (1+z)11 (1+z)4.5 Neutral fraction • Evolution of Ionization State: • Neutral fraction increases by >15 • Mean-free-path of UV photons decreases by >10 • Large variation in the IGM properties •  z~6 marks the end of cosmic reionization

  18. Three stages Pre-overlap Overlap Post-overlap From Haiman & Loeb

  19. What’s Next • Faint quasar survey at z~6: • In deep SDSS stripe • Additional 10 - 30 quasars at 1-2 mag fainter • Uses the upgraded MMT red channel -> new red-sensitive deep depletion CCD • Measures quasar luminosity function at z~6 • Probes the inhomogeneity of reionization by multiple line of sight • Future IR-based quasars surveys: • On UKIRT, VISTA • Allows detection at z~8-9 • JWST: • Probing the first light at z>10

  20. Probing Reionization History WMAP

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