1. Ranga-Ram Chary, Oct ’08 The First Billion Years of Galaxy Evolution Ranga-Ram Chary Spitzer Science Center/Planck Data Center California Institute of Technology, Pasadena, USA

2. Ranga-Ram Chary, Oct ’08 z=1.5 z=6 z=0 z=1000 Colleagues and Collaborators: Asantha Cooray (UCI) Ian Sullivan (Caltech) GOODS team (Earth) Edo Berger (Princeton) Len Cowie (Hawaii) Avi Loeb (Harvard) z=10

3. Ranga-Ram Chary, Oct ’08 What were the first sources that formed ? Which sources were responsible for reionizing the Universe? What was the reionization history of the Universe ? Did supermassive black holes form in the nucleus of dark matter halos before stars ? What was the luminosity function of the first galaxies and how does that relate to the dark matter halo mass function? How soon was dust produced in these galaxies ? What was the initial mass function of stars in the first galaxies ? What was the early metal enrichment history ? Outstanding Questions….

4. Ranga-Ram Chary, Oct ’08 λ<912Å photon Need 1 photon to start reionization Need ~10 photons to maintain ionized hydrogen due to recombinations Sensitive to: 1.Clumpiness of the gas 2.Temperature of the gas 3.Co-moving electron density

5. Ranga-Ram Chary, Oct ’08 Constraining Small HI Fractions at z~6 Fan et al., Becker et al., Djorgovski et al. spectra of Sloan quasars showing the Gunn-Peterson trough Evidence for N_H~<10 -3.5

6. Ranga-Ram Chary, Oct ’08 WMAP constrains large HI fractions WMAP 1σ range

7. Ranga-Ram Chary, Oct ’08 We can consider two reasonable scenarios which fit all existing data WMAP Tau = 0.084+/-0.016 z<6 contributes ~0.04 So 0.044+/-0.016 measures reionization history. Δz~3;  400 Myr Δz~9; ~700 Myr Now lets balance the ionizing photon budget and stay out of debt…….

8. Ranga-Ram Chary, Oct ’08 Detecting z>5 Galaxies/QSOs: Lyman Break Technique

9. Ranga-Ram Chary, Oct ’08 What were the sources of reionization ? Definitely galaxies – QSOs are too few But even galaxies are too few Yan & Windhorst ‘04

10. Ranga-Ram Chary, Oct ’08 1 deg A GOODS Field Cosmic Variance might be a Problem

11. Ranga-Ram Chary, Oct ’08 Minimum Required Evolution of UV Luminosity Density Slow Fast

12. Ranga-Ram Chary, Oct ’08 Some uncertainty in the faint end slope of the UVLF But clear evolution in L* between 6 and 7 Solid lines: Required for Reionization Dashed lines: Measured Data/fits from Bouwens et al. 08

13. Ranga-Ram Chary, Oct ’08 Predicted Evolution of the UVLF Slow reionization Evolving L* Slow reionization Constant L* at z>6 Fast reionization Constant L* at z>6 Fast reionization Evolving L* Dark Matter Halo Mass Function Chary & Cooray ‘08

14. Ranga-Ram Chary, Oct ’08 6 7 10 13 14 6 7 10 13 14 22 23 24 Fast Reionization Slow Reionization z Age(Gyr) 60.95 70.78 100.48 130.34 140.30 220.16 But L* has to be fixed at z>7! Otherwise faint end slope is too steep

15. Ranga-Ram Chary, Oct ’08 In principle, CIB measurements can reveal the difference

16. Ranga-Ram Chary, Oct ’08 Unfortunately Sky Background at Infrared Wavelengths is Dominated By Zodiacal Light CIRB (nW m -2 sr -1 ) I 2.2: 22.4  6.0 3.5: 11.0  3.3 140: 25  7 240: 14  3

17. Ranga-Ram Chary, Oct ’08 But to see the action, need the faint galaxies. And to see faint galaxies, need cosmic explosions which are x1000 brighter than the galaxy. GRB 050904 z=6.295 Kawai et al., Haislip et al. J-band R-band Can measure gas and metals in the galaxies.

18. Ranga-Ram Chary, Oct ’08 Hint of a higher SFR at z~6 from GRB Hosts Chary, Berger, Cowie, ApJ, 671

19. Ranga-Ram Chary, Oct ’08 Spitzer/GOODS data on ~60 z>5 Galaxies IRAC ch1 IRAC ch2 ACS z-band

20. Ranga-Ram Chary, Oct ’08 Spitzer detects about 50% of z>5 objects, mostly the brighter ones All Spitzer HAEs

21. Ranga-Ram Chary, Oct ’08 See also Yan et al, Bunker et al., Eyles et al., Stark et al. Massive Galaxies Have Larger Balmer Breaks = Older Stellar Population

22. Ranga-Ram Chary, Oct ’08 Detecting Hα from IRAC 4.5/3.6 micron ratios – technique works for QSOs Jiang et al. Sloan QSOs Flux Density

23. Ranga-Ram Chary, Oct ’08 Old galaxies can reproduce the red color, but not the UV flux Young galaxies Old galaxies More Hα

24. Ranga-Ram Chary, Oct ’08 Can fit SEDs and calculate SF History Difference is from Hα in emission ? UV SFR<10 M  /yr Hα SFR~100 M  /yr Hα EW~0.2 μm Chary et al. 05 Hu et al. 02 Schaerer et al. Indirect evidence for A V ~1 mag of dust within 1 Gyr of the Big Bang. But jury is out since no mm detection (Combes group).

25. Ranga-Ram Chary, Oct ’08 Constraints on Reionization if Dust were important For the measured star-formation rate and stellar mass density, reionization must be a brief process, lasting 20-50 Myr which happened between z~6-7 = INCONSISTENT WITH WMAP ! If reionization was a longer process starting at z~9, stellar mass density must be higher than measured OR more ionizing photons per baryon i.e. a top-heavy stellar mass function ρ*=10 7 M  /Mpc 3 ρ*=10 8 M  /Mpc 3

26. Ranga-Ram Chary, Oct ’08 Key parameters: Stellar Initial Mass Function Age of starburst Mass of stars Metals in stars Maybe SFR was higher in the past – due to e-folding time of burst or due to dust Nuisance Parameters: Clumping Factor Escape Fraction Chary, 2008, ApJ

27. Ranga-Ram Chary, Oct ’08 Balancing the Ionizing Photon Budget: A Simple Low Mass Cut in the IMF is Insufficient So, a top-heavy IMF at z>6 seems necessary. Furthermore, dust at high-z has been directly observed in QSOs.

28. Ranga-Ram Chary, Oct ’08 What were the first sources that formed ? –Star-forming galaxies with a LF which is similar to the DM halo mass function Which sources were responsible for reionizing the Universe? –Sub-L* star-forming galaxies What was the reionization history of the Universe ? –Slow reionization models are preferred where Δz(0.1,0.9)~9 How soon was dust produced in these galaxies ? –Seems to be within 800 Myr from QSO spectroscopy and candidate HAEs. Evidence for SN dust ? What was the initial mass function of stars in the first galaxies ? –Top-heavy, dN/dM~M -1.6 Conclusions