FIRST LIGHT IN THE UNIVERSE

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1 FIRST LIGHT IN THE UNIVERSE Richard Ellis, Caltech 1. Role of Observations in Cosmology & Galaxy Formation 2. Galaxies & the Hubble Sequence 3. Cosmic Star Formation Histories 4. Stellar Mass Assembly Saas-Fee, April Witnessing the End of Cosmic Reionization 6. Into the Dark Ages: Lyman Drop Outs 7. Gravitational Lensing & Lyman Alpha Emitters 8. Cosmic Infrared Background 9. Future Observational Prospects

Cosmic Star Formation Histories 4. Stellar Mass Assembly Saas-Fee, April 2006 5.

2 Witnessing the End of Cosmic Reionization Four important constraints put bounds on the epoch of cosmic reionization and the sources responsible: Evolution in the optical depth of Lyα absorption in high redshift QSOs (Fan et al Ap J in press, astro-ph/ ) Ubiquity of metals in the intergalactic medium (Songaila 2004) Large angular scale power in the temperature-polarization crosscorrelation function in the CMB (Kogut et al 2003, Spergel et al 2006) Assembled mass density at z~5-6 from HST/Spitzer probes of faint galaxies (Eyles et al 2005, Yan et al 2005, Stark & Ellis 2006) These motivate us to search the era z > 5 for star forming sources

Large angular scale power in the temperature-polarization crosscorrelation function in the CMB (Kogut et al 2003, Spergel et al 2006) Assembled mass density at

3 Gunn-Peterson Test

4 SDSS QSOs (2003) Cosmic variance along available sightlines τ GP = -ln T Do complete troughs mean reionization just ended at z=6.2? T = f(λ)/f cont Or is it just natural thickening of the forest as we move to higher z? Clue: as we approach end of reionization we expect abrupt change in optical depth τ GP with z 11 SDSS QSOs Fan et al (2003)

T = f(λ)/f cont Or is it just natural thickening of the forest as we move to higher z?

5 SDSS QSOs (2006) SDSS i-z colors in 6600 deg 2 used to locate 19 QSOs with 5.74<z<6.42 Combined analysis of Lyα,β,γ opacity used to verify τ GP (z): Wavelength ranges: Lyα: 1040 < λ (Å) < (1216) Lyβ: 970 < λ (Å) < (1040) Lyγ: 949 < λ (Å) < (970) ( ) - region affected by QSO ionization (proximity effect) excluded Fan et al (astro-ph/ )

Lyα: 1040 < λ (Å) < (1216) Lyβ: 970 < λ (Å) < (1040) Lyγ: 949 < λ (Å) < (970) ( ) -

6 E.g. using Ly alpha & Ly beta together Lyβ z QSO Lyα z QSO cosmic variance Lyβ Lyα Redshift

7 How GP effect works neutral fraction x HI So even tiny neutral fraction x HI ~10-4 gives a complete GP trough For reference x HI ~10-5 at z~0 But since τ GP f λ, for same n H, τ(lyβ), τ(lyγ) are <6.2,<17.9 smaller In practice, conversion from τ n HI depends on IGM clumpiness So absolute comparison of higher order Lyman lines more complicated than identifying relative trends in each

8 Comparing τ(lyα) ) and τ(lyβ) Lyα Lyβ Empirical argument; discontinuity seen in both samples: For z<5.5 τ(α) = 0.85[(1+z)/5] 4.3 ; τ(β) = 0.38[(1+z)/5] 4.3 Data for z > 5.5 is inconsistent: (1+z) Dispersion increases likewise: σ(τ) from This is the fundamental justification for the end of reionization

3 Data for z > 5.5 is inconsistent: (1+z) 10.

9 Combined Trend in τ GP (z) Combining the higher order Lyman lines on an absolute scale is hard

10 Is there really a break at z ~5.5? Raw transmission

11 Summary of the G-P Issues Optical depth τ is not very sensitive to ionized fraction Key issue is rate of change in τ(z): this distinguishes reionization (overlapping HII regions) from thickening in forest: do we see a break in trends as we approach z>6 Geometry important: knowing UV background can we directly infer sizes of Stromgren spheres at various z? Line of sight fluctuations and statistics of `dark gaps contains information on topology of late stages Are some lines of sight at z>6 still consistent with large neutral fraction?

Geometry important: knowing UV background can we directly infer sizes of Stromgren spheres at various z?

12 Scale of Ionized Regions Mean free path λ Extent of proximity effect At z > 5.7 mean free path of ionizing photons approximates clustering scale of SF galaxies, suggesting they are source of UV photons Declining extent of QSO s proximity effect: R [(1+z) x HI ] -1/3 suggesting higher z QSOs lie in a IGM whose x HI is 14 higher

galaxies, suggesting they are source of UV photons Declining extent of QSO s

13 Distribution of Dark Gaps Lyα Lyβ Gap or `void statistics contain useful information on topology Define `gap as contiguous region where τ > τ MIN (e.g. τ > 3.5) Regions of high transmission are effectively associated with large HII regions thus their distribution acts like an indirect Lyα LF: probe of neutrality independent of Gunn Peterson

5) Regions of high transmission are effectively associated with large HII regions

14 Metallicity of the Intergalactic Medium CIV forest is already present at z=4.5 Keck II + ESI 12 hrs Ubiquity of CIV in many sight-lines to z~5 indicates earlier SF Songaila & Cowie (2002, 2003)

15 Carbon also present in Lyα forest Lyα forest log f(n) Δz -1 log N(CIV) CIV was detected in the Lyα forest in 1995 with N(CIV)/N(HI)~ CIV is now seen in even the weakest Lyα systems (Ellison et al 2000) How did it get there? These are low column density HI systems Suggestive of ubiquitous enrichment from early times

in even the weakest Lyα systems (Ellison et al 2000) How did it get there?

16 Only Modest Evolution in Ω(CIV) CIV SiIV Songaila astro-ph/

17 First Year of WMAP Data CMB linear polarization powerful probe of e- scattering at recombination (1 deg) and reionization (>5 deg) TE cross power correlation function implies an electron scattering optical depth τ e = 0.17 ± 0.04 (Kogut et al 2003) If reionization was instantaneous: z = 17 ± 5 (Bennett et al 2003)

correlation function implies an electron scattering optical depth τ e = 0.

18 Putting the TE signal in context

19 More realistic reionization history (an example) Adopt WMAP cosmology and P-S formalism Assume fraction f of baryons collapse into bound objects and all energy IGM Solve for cooling, enrichment and ionization Complications (feedback, inhomogeneities) serve only to delay reionization Find z~10-12 since stars before reionization must contribute to τ Fukugita & Kawasaki (2003)

cooling, enrichment and ionization Complications (feedback, inhomogeneities) serve only to

20 Assume power law ΛCDM τ = 0.17±0.08 τ = 0.09±0.03 WMAP 3 year data Spergel et al (2006): instantaneous reionization at z=11±3 (2σ)

21 Recall: Balancing the Stellar Budget at z~0 Star formation history Mass assembly history GALEX, SDSS UV ACS dropouts Cole et al 2dF Spitzer FIR Integrating the SF history reproduces the stellar mass density at z~0

22 Assembled Stellar Mass at z~5-6 Integrated stellar mass density at z~5-6: M * (z) = z=10 z= 5 ρ * (z)dv (z) Now turn the argument around: Instead of checking that mass is consistent with past SF we can ask: What does accumulated stellar mass imply for earlier SF & reionization? If mass density at z~5-6 is greater than can be accounted for by previous SF history, options include: extinction: star formed but dust is present intrinsically faint contributors: lensing may find them upturn in SFH before z~10 Stark & Ellis New Astr. Rev. 50, 46 (2006)

23 Estimates of the Stellar Mass Density at z~5-6 GOODS v-drops and i-drops Cosmic age: τ ~ 1.2 Gyr (v) Gyr (i); z* AB ~24.5 (v) c.f (i) Spectroscopic confirmation + continuing Keck campaign (N>40) IRAC detection for stellar masses: key issue is the uncertainty in mass z=5.554, ~ M z=4.831, ~ M Stark, Bunker, Eyles, Ellis & Lacy 2006

24 Parameterized Star Formation History entire LF; α=-1.7 >0.1L* z=3 Based on recent compilations by Bouwens, Bunker et al

25 Measured z~5-6 Mass Density all SFH only accounts for mass assembled in SF galaxies at z~5, so still a lower limit Luminous SF galaxies Stark, Bunker, Eyles, Ellis & Lacy (2006)

26 Summary of Lecture #5 We have discussed 4 completely independent and indirect probes of cosmic reionization each of which suggests activity - probably involving stars - in the interval 6<z<12 The HI troughs in SDSS QSOs - the arguments are compelling but rely on a subtle change in properties below and above z~5.5 Ubiquity of metals in deep intergalactic space - they can only have got there from an early period of SF z>5 WMAP polarization from electron scattering - not as precise a pointer to the redshift of activity as reported The remarkable amount of assembled mass at z~5 - perhaps the best pointer to much SF z>5

The Birth and Assembly of Galaxies: the Relationship Between Science Capabilities and Telescope Aperture

The Birth and Assembly of Galaxies: the Relationship Between Science Capabilities and Telescope Aperture Betsy Barton Center for Cosmology University of California, Irvine Grateful acknowledgements to: