z=1.5

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

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

3. Outstanding Questions…. • 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 ? Ranga-Ram Chary, Oct ’08

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

5. 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 Ranga-Ram Chary, Oct ’08

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

7. 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~9; ~700 Myr Δz~3; 400 Myr Now lets balance the ionizing photon budget and stay out of debt……. Ranga-Ram Chary, Oct ’08

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

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

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

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

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

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

14. 6 7 10 13 14 z Age(Gyr) 6 0.95 7 0.78 10 0.48 13 0.34 14 0.30 22 0.16 Fast Reionization 6 7 10 13 14 22 23 24 But L* has to be fixed at z>7! Otherwise faint end slope is too steep Slow Reionization Ranga-Ram Chary, Oct ’08

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

16. 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 Ranga-Ram Chary, Oct ’08

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

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

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

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

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

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

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

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

25. Constraints on Reionization if Dust were important ρ*=107 M/Mpc3 ρ*=108 M/Mpc3 • 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 Ranga-Ram Chary, Oct ’08

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

27. 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. Ranga-Ram Chary, Oct ’08

28. Conclusions • 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 Ranga-Ram Chary, Oct ’08