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

The Highest Redshift Quasars Today z>4: >900 known z>5: >50 z>6: 8 SDSS i-dropout Survey: –By Fall 2004: 6000 deg 2 at z AB <20 –Sixteen luminous quasars at z>5.7 –Many L and T brown dwarfs ~30 at z~6 expected in the whole survey

Exploring the Edge of the Universe New z~7 galaxies

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

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 5x10 6 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

What Reionized the Universe? Based on SDSS quasar luminosity function: –Low-density + relatively flat LF – UV photons from luminous quasars and AGNs are not the major sources that ionized the universe

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

Strong Evolution of Gunn-Peterson Optical Depth Fan et al 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 The evolution of G-P optical depth: –Tracking the evolution of UV background and neutral fraction of the IGM –Probe the ending of reionization

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

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 Fan et al. 2002, 2005 Photoionizing rate

Gunn-Peterson Troughs in the Highest-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 z abs <5.8 –Transition happens at z>5.8… But LOS variation is significant…

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

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

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?

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

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 Fan et al. in prep mass ave. vol. ave

Size of Stromgren Sphere 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 10 7 yr lifetime  n(HI) higher than 10% at least for some line of sight –Calculation dependent on lifetime as well as detailed radiative transfer… Wyithe and Loeb, Mesinger and Haiman

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? ?

Probing the Reionization Epoch before 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

Probing the first Metals in the IGM? 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 10 hour Keck/ESI J

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 ?

Probing the Reionization Epoch before 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