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

Ranga-Ram Chary, Oct 08

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

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08What 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.

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Need 1 photon to start reionizationNeed ~10 photons to maintain ionized hydrogen due to recombinationsSensitive to:Clumpiness of the gasTemperature of the gasCo-moving electron density

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Constraining Small HI Fractions at z~6Fan et al., Becker et al., Djorgovski et al. spectra of Sloan quasars showing the Gunn-Peterson troughEvidence for N_H~

Ranga-Ram Chary, Oct 08WMAP constrains large HI fractionsWMAP 1 range

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08We can consider two reasonable scenarios which fit all existing dataWMAP Tau = 0.084+/-0.016

z

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

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08What were the sources of reionization ?Definitely galaxies QSOs are too fewBut even galaxies are too fewYan & Windhorst 04

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Ranga-Ram Chary, Oct 081 degA GOODS FieldCosmic Variance might be a Problem

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Ranga-Ram Chary, Oct 08Minimum Required Evolution of UV Luminosity DensitySlowFast

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Some uncertainty in the faint end slope of the UVLFBut clear evolution in L* between 6 and 7Solid lines: Required for ReionizationDashed lines: MeasuredData/fits fromBouwens et al. 08

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Ranga-Ram Chary, Oct 08Predicted Evolution of the UVLFSlow reionizationEvolving L*Slow reionizationConstant L* at z>6Fast reionizationConstant L* at z>6Fast reionizationEvolving L*Dark Matter HaloMass FunctionChary & Cooray 08

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Ranga-Ram Chary, Oct 086 7 10 13 146 7 10 13 14 22 23 24Fast ReionizationSlow Reionizationz Age(Gyr)60.9570.78100.48130.34140.30220.16But L* has to be fixed at z>7!Otherwise faint end slope is too steep

Ranga-Ram Chary, Oct 08

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

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Unfortunately Sky Background at Infrared Wavelengths is Dominated By Zodiacal LightCIRB (nW m-2 sr-1) I2.2: 22.46.03.5: 11.03.3140: 257240: 143

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08But to see the action, need the faint galaxies.And to see faint galaxies, need cosmic explosions which are x1000 brighter than the galaxy.GRB 050904z=6.295Kawai et al., Haislip et al.J-bandR-bandCan measure gas and metalsin the galaxies.

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

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Ranga-Ram Chary, Oct 08Spitzer/GOODS data on ~60 z>5 GalaxiesIRACch1IRACch2ACS z-band

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Ranga-Ram Chary, Oct 08Spitzer detects about 50% of z>5 objects, mostly the brighter onesAllSpitzerHAEs

Ranga-Ram Chary, Oct 08

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

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Detecting H from IRAC 4.5/3.6 micron ratios technique works for QSOsJiang et al. Sloan QSOsFlux Density

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Old galaxies can reproduce the red color, but not the UV fluxYoung galaxiesOld galaxiesMore H

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Can fit SEDs and calculate SF HistoryDifference is from H in emission ?

UV SFR

Ranga-Ram Chary, Oct 08Constraints on Reionization if Dust were importantFor 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*=107 M/Mpc3*=108 M/Mpc3

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Key parameters:Stellar Initial Mass FunctionAge of starburstMass of starsMetals in starsMaybe SFR was higher in the past due to e-folding time of burst or due to dustNuisance Parameters:Clumping FactorEscape FractionChary, 2008, ApJ

Ranga-Ram Chary, Oct 08

Ranga-Ram Chary, Oct 08Balancing the Ionizing Photon Budget: A Simple Low Mass Cut in the IMF is InsufficientSo, 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

Ranga-Ram Chary, Oct 08What 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 z(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-1.6Conclusions

Ranga-Ram Chary, Oct 08

****Larger uncertainty in estimation of cosmic near-infrared background because of larger and uncertain zodiacal light contribution******