Observational Constraints of Observational Constraints of the Epoch - PowerPoint PPT Presentation

Observational Constraints of Observational Constraints of the Epoch of the Epoch of Reionization Reionization Xiaohui Fan Fan Xiaohui University of Arizona University of Arizona Collaborators: Becker, Carilli, Ferrara, Gallerani , Gnedin, Jiang , Richards, Roy Choudhury, Strauss, Xu , Walter, White, et al. Background: 46,420 Quasars from the SDSS Data Release Three

reionization Two Key Constraints: 1. WMAP 3-yr: z reion =10+/-3 2. IGM transmission: z reion > 6 From Avi Loeb

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

Open Questions: • When : Early or Late – z~6: late – z~15: early • How did reionization proceed: – Phase transition or gradual? – Once or twice? – Homogeneous or large scatter? • What did it: – AGN? – Star formation? – Decay particles? • Observational goals – Map the evolution of ionization state: neutral fraction (f HI ) vs. redshift – Find highest redshift galaxies and quasars: source of reionization

WMAP: early reionization? • Thompson scattering of CMB photons by free electrons during/after z reion = 6 reionization --> polarization • WMAP third year: – τ = 0.09+/- 0.03 – Larger signal comparing to late reionization model (but marginally consistent!) Page et al., Spergel et al. 2006

WMAP: early reionization • Inconsistent with a phase transition at z=6 at 2 σ level • Reionization could starts at z=10-15 • However, no direct conflict to Gunn-Peterson result, which is sensitive Spergel et al. 2006 only to ~1% neutral IGM • Overlapping could still be at z~6 • IGM could have complex reionization history ⇒ direct observation of high-z sources Gnedin 2004

Quest to the Highest Redshift Quasars IR survey (UKIDSS, VISTA) SDSS • APM CCD Radio

The Highest Redshift Quasars Today • z>4: >1000 known • Other on-going z~6 quasar • z>6: 19 surveys: • SDSS i-dropout Survey: – AGES (Cool et al.): Spitzer – Completed in June 2006: selected, one quasar at z=5.8 • 7700 deg 2, z AB < 20 – FIRST-Bootes (Becker et al.): radio selected, one quasar at • 27 luminous quasars at z=6.1 5.71<z<6.42 – QUEST: i-dropout surveys • CFHT High-z Quasar Survey similar to SDSS (CFHTQS, Willott et al. astro- – IR-based survey: UKIDSS, ph/0706091) (z=5.83), VISTA , allows – Goal: 400 deg 2 , z AB <22.5 detection up to z~8-9. – 4 quasars at z>6 – New highest-z quasar at z=6.43 • SDSS Faint Quasar Survey (SFQS) : – faint quasars in the deep SDSS stripe (Jiang, XF et al.), 300 deg 2 , z AB < 22.5 – – six z~6 quasar at 20 < z AB < 21 – Goal: quasar LF

Quasar Density at z~6 • From SDSS i-dropout survey – Density declines by a factor of ~40 from between z~2.5 and z~6 • Cosmological implication – M BH ~10 9-10 M sun – M halo ~ 10 12-13 M sun – rare, 5-6 sigma peaks at z~6 (density of 1 per Gpc 3) • Assembly of supermassive BHs? – The universe is only ~20 t eddington old, requiring non-stop Eddington accretion of 100 M sun from z>>20 – Is Eddington-limited accrection from stellar seeds still permitted, or are alternative accretion modes (super-Eddington, intermediate mass BH) needed? Fan et al. 2006

The Lack of Evolution in Quasar Emission Line Properties The Lack of Evolution in Quasar Emission Line Properties z~6 composite Ly a Low-z composite NV OI SiIV Ly a forest Fan et al.2007 • Rapid chemical enrichment in quasar vicinity • Quasar env has supersolar metallicity : no metallicity evolution • High-z quasars are old, not yet first quasars..

Quasar Metallicity at z~6 near-IR spectroscopy: Gemini + VLT Jiang, XF et al. 2007

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 at z~6

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

Evolution of Lyman Absorptions at z=5-6 Δ z = 0.15

Accelerated Evolution at z>5.7 • Optical depth evolution accelerated – z<5.7: τ ~ (1+z) 4.5 (1+z) 11 – z>5.7: τ ~ (1+z) >11 – End of reionization? • Dispersion of optical depth also increased – Some line of sight have dark (1+z) 4.5 troughs as early as z~5.7 – But detectable flux in ~50% case at z>6 – End of reionization is not uniform, but with large scatter XF et al. 2006

Evolution of Ionization State UV background • UV Ionizing background: – Assuming photoionization and model of IGM density distribution – UV background declines by close to an order of magnitude from z~5 to 6.2 – Increased dispersion suggests a highly non-uniform UV background at z>5.8 Neutral fraction • From GP optical depth measurement, volume averaged neutral fraction increase by >~ order of magnitude from z~5.5 to 6.2 XF et al. 2006

Reionization overlap at z~6-7? • Comparing G-P observations with high-resolution reionization simulation: – Overlap redshift ~6.2 – Current simulation does not resolve earliest star formation to predict an accurate CMB polarization optical depth Gnedin and Fan 2006

Evolution of Proximity Zone Size Around Quasars Shapiro, Haiman, Mesinger, Wyithe, Loeb, Bolton, Haehnelt, Maselli et al. Proximity zone size (Mpc) • Size of Proximity Zone region R p ~ (L Q t Q / f HI ) 1/3 • Size of quasar proximity zone decreases by a factor of ~2.4 between z=5.8 and 6.4 (Fan et al. 2006) • Consistent with neutral fraction increased by a factor of ~15 over this narrow redshift range • Can be applied to higher z and f HI with lower S/N data • Actual size of proximity zone dependent on details of radiative transfer and quasar redshift XF et al. 2006 model…

Dark Gap Distributions • Dark gap statistics (Songaila & Cowie 2002) – Gaps: regions where all pixels have τ >2.5 • Gaps among z~6 quasars – Average length shows the most dramatic increase at z>5.8 → IGM is dominated by long, dark gaps • Consistent with overlap at z~6-8? – Dispersions • Even at z>6, gap lengths are still finite • Upper limit on neutral fraction – If IGM largely neutral, GP damping wing will wipe out all HII region transmissions – Existence of transmission at z>6 places an upper limit of average neutral fraction <30% (Gallerani et al. 2007) – Independent upper limit on neutral fraction XF et al. 2006

Ly α Galaxy LF at z>6 Iye et al. 2006 Kashikawa et al. 2006 • Neutral IGM has extended GP damping wing → attenuates Ly α emission line • New Subaru results – Declining density at z~6-7 (2-3 σ result) – Reionization not completed by z~6.5 – Neutral fraction could be as high as a few tenths but strongly model-dependent – cf. Malhotra & Rhoads, Hu et al.: lack of evolution in Ly α galaxy density

GRBs as Probes of Reionization Damping wing? GRB050904 • Detected to z=6.30 • Advantages: – Bright – Flat K-correction due to time dilation at high-z – Small surrounding HII regions: could use damping wing of Gunn- Peterson trough to probe high neutral fraction • Constraining neutral fraction – How to distinguish internal Kawai et al. 2005 absorption from IGM damping wing?? – Using 050904: f HI < 0.6 (2- sigma) by fitting both DLA and IGM profiles

Probing Neutral Era • 21cm probes: – HI emission during reionization – 21cm Gunn-Peterson effects in high-z radio sources Gnedin & Shiver McQuinn et al. Carilli et al. • Metal absorption lines (Oh 2002, Becker et al. 2005) • Ly α galaxy distributions (e.g. Malhotra and Rhoads); G-P gap distribution • GRBs

What Ionized the Universe? AGNs or Galaxies Density of quasars SFR of galaxies • Quasar LF at z~6: – SDSS Wide: 7700 deg 2 , 17 quasars, z AB <20 – SDSS Deep: ~150 deg 2 , 6 quasars, 20<z AB <21 – AGES: 1 quasar in 5 deg 2 at z AB <21.5 • Steeppening of LF: – Φ∝ L -3.1 Φ∝ – Comparing to Φ∝ L -2.4 at z~4 Jiang, XF et al. 2007

Reionization by AGNs? • Can quasars do it? – Too few quasars unless QLF remains to be steep to AGN luminosity • Can low-luminosity AGNs ionize the IGM by z~6? – Stacking X-ray image of LBGs in UDF… too few faint AGNs • Can accretion to seed BHs ionize the IGM by z~15? – Dijkstra, Haiman & Loeb (2004) – – Soft X-ray background Soft X-ray background overproduced if quasars if quasars overproduced produce ~10 photons/H atom produce ~10 photons/H atom – – ‘Preionization ‘ Preionization’ ’ to to f f(HI)~50% (HI)~50% by X-rays is still allowed (e.g. by X-rays is still allowed (e.g. Ricotti et al.) Ricotti et al.) Jiang, XF et al. 2007

Reionization by stellar sources? by stellar sources? Reionization Necessary for reionization 6<z<9 (Stiavelli et al 2003) Bouwens & Illingworth; Bunker et al. • Large uncertainties in reionization photon budget: – IGM clumpiness – UV radiation and escape efficiency – Large cosmic variance in deep field data – Galaxy luminosity function at high-z