Ranga-Ram Chary, Oct ’08 The First Billion Years of Galaxy Evolution Ranga-Ram Chary Spitzer...

Ranga-Ram Chary, Oct ’08

The First Billion Years of Galaxy EvolutionRanga-Ram Chary

Spitzer Science Center/Planck Data CenterCalifornia Institute of Technology, Pasadena, USA


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


• 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….


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

gas2. Temperature of the

gas3. Co-moving electron

density


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


WMAP constrains large HI fractions

WMAP 1σ range


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+/-0.016measures reionization history.

Δz~3; 400 Myr

Δz~9; ~700 Myr

Now lets balance the ionizing photon budget and stay out of debt…….


Detecting z>5 Galaxies/QSOs: Lyman Break Technique


What were the sources of reionization ?

Definitely galaxies – QSOs are too few But even galaxies are too fewYan & Windhorst ‘04


1 deg

A GOODS Field

Cosmic Variance might be a Problem


Minimum Required Evolution of UV Luminosity Density

Slow

Fast


Some uncertainty in the faint end slope of the UVLFBut clear evolution in L* between 6 and 7

Solid lines: Required for ReionizationDashed lines: Measured

Data/fits fromBouwens et al. 08


Predicted Evolution of the UVLF

Slow reionizationEvolving L*

Slow reionizationConstant L* at z>6

Fast reionizationConstant L* at z>6

Fast reionizationEvolving L*

Dark Matter HaloMass Function

Chary & Cooray ‘08


6 7 10 13 14

6 7 10 13 14 22 23 24

Fast Reionization

Slow Reionization

z Age(Gyr)

6 0.95

7 0.78

10 0.48

13 0.34

14 0.30

22 0.16

But L* has to be fixed at z>7!Otherwise faint end slope is too steep


In principle, CIB measurements can reveal the difference


2.2 micron contributions

74%

14%

12% 0%

Zodiacal LightStarsCIRBISM

140 micron contributions

37%

27% 36%

Zodiacal Light

CIRBISM

Unfortunately Sky Background at Infrared Wavelengths is Dominated By Zodiacal Light

CIRB (nW m-2 sr-1) I

2.2: 22.46.03.5: 11.03.3140: 257240: 143


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 050904z=6.295Kawai et al., Haislip et al.

J-band R-band

Can measure gas and metalsin the galaxies.


Hint of a higher SFR at z~6 from GRB Hosts

Chary, Berger, Cowie, ApJ, 671


Spitzer/GOODS data on ~60 z>5 Galaxies

IRACch1

IRACch2

ACS z-band


Spitzer detects about 50% of z>5 objects, mostly the brighter ones

All

Spitzer

HAEs


See also Yan et al, Bunker et al., Eyles et al., Stark et al.

Massive Galaxies Have Larger Balmer Breaks = Older Stellar Population


Detecting Hα from IRAC 4.5/3.6 micron ratios – technique works for QSOs

Jiang et al. Sloan QSOs

Flu

x D

ensi

ty


Old galaxies can reproduce the red color, but not the UV flux

Young galaxies Old galaxies

Mor

e H

α


Can fit SEDs and calculate SF HistoryDifference is from Hα in emission ?

UV SFR<10 M/yrHα SFR~100 M/yr

Hα EW~0.2μm

Chary et al. 05Hu et al. 02Schaerer et al.

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).


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*=107 M/Mpc3 ρ*=108 M/Mpc3


Key parameters:Stellar Initial Mass FunctionAge of starburstMass of starsMetals in stars

Maybe SFR was higher in the past – due to e-folding time of burst or due to dust

Nuisance Parameters:Clumping FactorEscape Fraction

Chary, 2008, ApJ


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.


• 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

Ranga-Ram Chary, Oct ’08 The First Billion Years of Galaxy Evolution Ranga-Ram Chary Spitzer...

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