1. The Most Distant Quasars: Probing the End of Cosmic Dark Ages Xiaohui Fan Steward Observatory The University of Arizona

2. The SDSS Collaboration

3. The Most Distant Quasars: Probing the End of Cosmic Dark Ages Xiaohui Fan Steward Observatory The University of Arizona

4. 40 Years Ago: First Quasar: 3C 273 by Maarten Schmidt

5. 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

6. Exploring the Edge of the Universe

7. SDSS at Your Service Courtesy of Arizona graduate students

8. The Highest Redshift Quasars Today z>4: ~700 known z>5: ~30 z>6: 6 Highest redshift: z=6.42 SDSS Discoveries Total Discoveries

9. 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.

10. SDSS Overview Primary Telescope: 2.5m wide-field (2.5 deg) Imaging Survey (wide-field 54 CCD imager) –Main Survey: 10000 deg 2 –Five bands, 3000 – 10000 Å – r lim ~ 22.5, z lim ~ 20.5 Spectroscopic Survey –10 6 galaxies (r<17.8) –10 5 quasars ( 0 < z < 6.5) –Interesting stars, radio/x-ray sources etc.

11. 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=3 Z=4 Z=5 Richards, Fan, Newberg, Strauss, et al. 2002

12. 17,000 Quasars from the SDSS Data Release One wavelength 4000 A9000 A redshift 0 1 2 3 5 Ly a CIV CIII MgII Ha OIII

13. 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 deg 2 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.

14. 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

15. 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 spectroscopic Identification (~50 objects) 4. Detailed spectra (12 new quasars at z~6) Keck 10m Hobby-Eberly 9.2m Kitt Peak 4m MMT 6.5m

16. z~6 Quasars SDSS i-dropout Survey: –By Dec 2003: 5000 deg 2 at z AB <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

18. The Lack of Evolution in Quasar Intrinsic Spectral Properties NV OI SiIV Ly a Ly a forest Fan et al. 2004

19. 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. 2001 Barth et al. 2003

20. 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 –M BH ~10 9-10 M sun –M halo ~ 10 13 M sun –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.

21. Sub-mm and Radio Observation of 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 ~ 10 8 M sun If dust heating came from starburst  star forming rate of 500 – 2000 M sun /year  Quasars are likely sites of intensive star formation Arp 220 Bertoldi et al. 2003

22. Submm and CO detection in the highest-redshift quasar: Dust mass: 10 8 – 10 9 M sun H 2 mass: 10 10 M sun Star forming rate: 10 3 /yr  co-formation of SBH and young galaxies

23. Co-evolution of early galaxies and supermassive BHs Presence of 10 9-10 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

24. 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

25. A brief cosmic history  recombination  Cosmic Dark Ages: no light no star, no quasar; IGM: HI  First light: the first galaxies and quasars in the universe  Epoch 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  today Courtesy: G. Djorgovski

26. Gnedin 2000 Neutral fractionUV background Gas densityGas temperature

27. Gnedin 2000 Neutral fractionUV background Gas densityGas temperature

28. The end of dark ages: Movie Courtesy of N. Gnedin

29. Increasing Lyα absorption with redshift: z abs f obs /f con --------------------------- ~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

30. VLT/FOS2 Pentericci et al. 2002

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

32. Gunn-Peterson troughs confirmed by new z>6 quasars

33. Strong Evolution of Gunn-Peterson Optical Depth Fan et al. 2004 Transition at z~5.7?

34. 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

35. 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

36. 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

37. Comparing with Models postoverlap overlapping epoch Pre- overlap Volume-averageed Mass-averaged Fan et al. 2002

38. 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

39. 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

40. 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