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Probing the End of Reionization with High-redshift Quasars

Probing the End of Reionization with High-redshift Quasars. Xiaohui Fan University of Arizona Mar 18, 2005, Shanghai Collaborators: Becker, Gunn, Lupton, Narayanan, Penterrici, Richards, Rix, Strauss, White et al. And SDSS collaboration. Courtesy of Arizona graduate students.

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Probing the End of Reionization with High-redshift Quasars

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  1. Probing the End of Reionization withHigh-redshift Quasars Xiaohui Fan University of Arizona Mar 18, 2005, Shanghai Collaborators: Becker, Gunn, Lupton, Narayanan, Penterrici, Richards, Rix, Strauss, White et al. And SDSS collaboration

  2. Courtesy of Arizona graduate students

  3. The Highest Redshift Quasars Today • z>4: >900 known • z>5: >50 • z>6: 8 • SDSS i-dropout Survey: • By Fall 2004: 6000 deg2 at zAB<20 • Sixteen luminous quasars at z>5.7 • Many L and T brown dwarfs • ~30 at z~6 expected in the whole survey

  4. Existence of SBHs at the end of Cosmic Dark Ages BH accretion history in the Universe? Relation of BH growth and galaxy evolution? High-redshift Quasars and the End of Cosmic Dark Ages Resolved CO emission from z=6.42 quasar • Probing the end of reionization? Evolution of Quasar Density Detection of Gunn-Peterson Trough

  5. 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

  6. Keck/ESI 30min exposure  Gunn-Peterson Trough in z=6.28 Quasar Keck/ESI 10 hour exposure  White et al. 2003

  7. Strong Evolution ofGunn-Peterson Optical Depth Transition at z~5.7? Fan et al. 2004

  8. 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 • The evolution of G-P optical depth: • Tracking the evolution of UV background and neutral fraction of the IGM • Probe the ending of reionization

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

  10. Evolution of Ionizing Background • Ionizing background estimated by comparing with cosmological simulations of Lyman absorption in a LCDM model • Ionizing background declines by a factor of >25 from z~3 to z~6 • Indication of a rapid decline at z>5.7… • Marks the tail end of reionization – overlapping of individual HII regions – at z~6 Photoionizing rate Fan et al. 2002, 2005

  11. Gunn-Peterson Troughs in theHighest-redshift Quasars • Four quasars known at z>6.2 • Strong, deep Lyα and Lyβ absorption in all four objects immediately blueward of Lyα emission… • None of the quasars at z<6.2 shows any G-P troughs • There is no Gunn-Peterson trough at zabs<5.8 • Transition happens at z>5.8… • But LOS variation is significant…

  12. Line of Sight Difference… Completely dark G-P trough universe highly ionized in this line of sight! White et al .2003

  13. Leaky IGM at z~6 • Deep narrow band ACS imaging • Lyβ transmission point-like, coincides with quasar position  IGM transmission at z~6, not intervening galaxies, not lensed… • Gunn-Peterson Ly γ trough  τ < 15, line of sight highly ionized (Oh & Furlanetto 2004) White, Becker, Fan and Strauss 2004

  14. Line of sight variations at the end of overlapping? • The “last transmitting” redshift ranges from 5.85 to 6.15 • Non-uniform reionization? • Expected if ionizing sources rare/clustered and HII bubbles have large sizes?

  15. Size of ionized bubbles at the end of reionization • Wyithe and Loeb (2004) • Completion of overlapping determined by the light crossing time of HII bubbles larger than the scattering of bubble formation time • Scatter in the overlapping redshift of the order Δz ~ 0.13, with a bubble size of 60 co-moving Mpc at z~6 • Consistent with scatter seen in the last transmission redshift of z~6 quasars

  16. Constraining the Reionization Epoch • Neutral hydrogen fraction • Volume-averaged HI fraction > 0.1% at z~6 • From G-P alone: • There is still a long way to go from τ>10 to τ~100,000 • Gunn-Peterson test only sensitive to small neutral fraction and saturates at large neutral fraction • Need more sensitive tests to probe larger neutral fraction mass ave. vol. ave Fan et al. in prep

  17. Sharp transition at the end of quasar proximity zone implies the boundary of HII region around quasar Size of HII region a function of quasar life-time and neutral fraction of the IGM Assume 107 yr lifetime  n(HI) higher than 10% at least for some line of sight Calculation dependent on lifetime as well as detailed radiative transfer… Size of Stromgren Sphere Wyithe and Loeb, Mesinger and Haiman

  18. Put the picture together • G-P results: overlapping might be happening at z~6 or slightly earlier • CMB polarization shows: substantial ionization by z~17 • These two measurements are not contradictory; combining GP with CMB  complex reionization history: • First star formation happens very early? • Reionization last from 20 to 6? (600 million years) • Reionization is not a phase transition • Multiple episodes of reionization? ?

  19. Probing the Reionization Epochbefore JWST • More lines of sight from high-redshift quasars • About 20 – 40 quasars 6 < z < 6.6 from SDSS • Spectroscopy in far-optical and near-IR with large telescopes • G-P test: probing non-uniformity of the end of reionization • Metal absorption lines at z>6

  20. Probing the first Metals in the IGM? 10 hour Keck/ESI J1148+5251 • 5 – 10 hour exposure in the far-optical and • near-IR of z~6 quasars on 6 – 10m class telescope • High S/N to detect intergalactic CIV and SiIV absorption To probe the metal density of the IGM at z>5

  21. Evolution of IGM CIV density • No redshift evolution of CIV density from z~2 to 5 • IGM enriched in metal at z>>5 • Future observations: • Near IR spectroscopy: metals at z~6 • How does the IGM enrichment history trace the reionization history? • Provide more sensitive probe to the neutral fraction? ? Pettini et al. 2003

  22. Probing the Reionization Epochbefore JWST • More lines of sight from high-redshift quasars • About 20 – 40 quasars 6 < z < 6.6 from SDSS • Spectroscopy in far-optical and near-IR with large telescopes • G-P test: probing non-uniformity of the end of reionization • Metal absorption lines at z>6 • Looking for objects at z>7: first sources of light • z~6.6 is the limit of optical survey  IR searches, UKIDSS, VISTA etc. • High-redshift GRBs: SWIFT!!! • 21cm mapping of reionization  mapping the complete history of reionization and early galaxy formation

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