History of Cosmological Reionization Renyue Cen Princeton University Observatory @End of Dark Ages Workshop (STScI) March 14, 2006 History of cosmic structure formation Observational constraints on reionization Reionization process calculations Numerical radiative transfer simulations Detecting first galaxies Conclusions

The Standard Cosmological Model Adiabatic, Gaussian, scale-free density perturbation --- Baryons 5% --- Cold Dark Matter 23% --- Dark Energy (cosmological constant?) 72% n=0.99, s8 = 0.9, Wbh2=0.024, Wxh2 = 0.126, H0 = 72, L0= 0.71 (subject to adjustments in 2 days) Spergel etal (2003) consistent with: Inflation Light element nucleosynthesis q0 from SNe Ia H0 (HST key project, SNe Ia) Age of the universe (stellar evolution) WHIM

Cosmic Timeline in Standard Model 0.0003 Time  13 Gyr  Redshift 106K z=1100 30 – 15 10-6 6 - 1 1 - 0 Recom- bination Real Dark Ages Pop III Stars Galaxies Quasars 1st Reion 2nd gen Galaxies Quasars Final Reion Lya forest Majority of Quasars Ellipticals Majority of Galaxy Clusters LSS 3000 K 10000 K Temp 100K Hierarchical structure formation        …………………………………..       Log(Mnl) 105 106 108 109 1012 1014

Naïve implication: te=0.03-0.04 Observ. Constraints on Reionization 1: SDSS QSOs: neutral hydrogen fraction changes from 10-4 to >10-2 from z=5.8 to 6.3 Cen & McDonald (2002) Fan et al (2002) SDSS 1030+0524 z=6.28 Put Fan fig6 here Naïve implication: te=0.03-0.04

White, Becker, Fan, Strauss (2003) More new z>6 quasars White, Becker, Fan, Strauss (2003)

(assuming x=nHI/nHtot=0) 2: WMAP (1st Yr): te=0.17 +- 0.04 Kogut et al. 2003 Bennett et al (2003) What does it mean? zri=20+10 -9 (assuming x=nHI/nHtot=0)

Hui & Haiman 2003; Theuns et al 2002 3: Lya forest: zri < 9-10 Hui & Haiman 2003; Theuns et al 2002 Hui & Haiman (2002)

One viable pre-WMAP physical model: Solution: Prolonged Reionization Process One viable pre-WMAP physical model: Universe Was Reionized Twice! (Cen 2003a; Wyithe & Loeb 2003)

What could reionize the universe early: More ionizing photons wanted Quasar space density Star formation rate (Haiman, Abel & Madau 2001) log [d* /dt / M yr-1 Mpc-3] log [n(z) / n(peak)] redshift 2 1 ? ? -1 Z Z

IMF for Population III (First) Stars Recent theoretical works suggest a new picture for Pop III IMF (Nakamura & Umemura 2001, 2002; Abel et al 2002; Bromm et al 2002): Pop III IMF may be very top-heavy, possibly with most of the stars with mass >~ 100 Msun top row: 1/1000 of a box volume from z=100, to z=18.2 middle row: z=18.2 only and continuously zoom in bottom row: z=18.2 only Abel et al (2002)

top row: 1/1000 of a box volume from z=100, to z=18.2 middle row: z=18.2 only and continuously zoom in bottom row: z=18.2 only Bromm et al (2002)

The mass of Pop III stars is likely due to stellar feedback processes Tan & McKee (2002, 2004): The mass of Pop III stars is likely to fall in the range of M = 30-100 Msun due to stellar feedback processes T=300 K due to H2 cooling And n=1.e-4 /cm^3, the critical density Of H2 rotational-vibrational line cooling, Yields total core mass of 10^3 Msun. These cores collapse inside-out to form A protostar, which then grows rapidly In mass, through accretion in a disk. Below 30Msun feedback is not important But above 100Msun feedback becomes The bottleneck due to (1) HII region Breakout to large distances where Escape velocity equals the the Sound speed of 10km/s And (2) Lyman-alpha and FUV pressure In the HII region.

Observ. Case: Massive Pop III Stars M>140 Msun: PISN after core He depletion (Hedge and Woosley 2002), explosive O and Si Burning . This instability quickly disrupts. The star, ejects metals and leaves no remnant. Because it is triggered at an unusually Early stage in the star’s evolution. This PISN produces an unusual nucleosynthetic signature, which could appear in the second generation EMP (extremely metal poor) stars in the Galactic halo. Qian Wasserburg (2002) and Oh et al. (2001) used this idea to argue that these stars justify the VMS hypothesis. When M>260Msun, as the temperatures Resulting from PI collapse are great enough To photodisintegrate nuclei, which counters explosive oxygen and silicon burning (Fryer, Woosley & Heger 2001; Heger & Woosley 2002). Little mass ejection and metal enrichment from such supernovae. M=40-140: form BHs with relatively inefficient metal ejection. M<40: form neutron stars with more normal enrichment rates (however, see Umeda & Nomoto 2003 with mixing and fallback. There are 3 clear features in Galactic halo EMP Abundances: specific Fe-peak element ratios (especially Zn), the widespread presence of r-process elements, and elevated [C,N,O/Fe] ratios. Iron-peak elements (Cr-Zn): produced in explosive events r-Process elements (A>100): these elements are thought to be produced by rapid neutron capture in hot, dense, neutron-rich environments during explosive events. Associated with stars M=8-40Msun. The absolute abundances and relative ratios of r-process elements are thus sensitive indicators of core-collapse supernova activity. The mean [r/Fe] is similar to the solar value at all [Fe/H], but with up to 2 dex scatter at [Fe/H]~-3. The relative abundances (i.e., [Eu/Ba] are also similar to the solar values. Primary elements (C,N,O): of these direct products of main-sequence stellar nucleosynthesis, C is easily found in EMPs, but N and O are difficult to measure. Many EMP stars are C-rich relative to Fe. Tumlinson et al. (2004 argue that VMS have no significant post-He nuclear burning and therefore produce no r elements (HW02). If VMS produce all the Fe up to [Fe/H]~-3, the r elements should be absent instead of appearing at [r/Fe]~ -0.5 as observed. Wasserburg & Qian (2000) argue that the qualitative change in [r/Fe] at [Fe/H]~-3 presented an ``iron conundrum”; namely, that the wide dispersion in Eu and Ba abundances at [Fe/H}~-3 suggested unrelated sources of Fe and r elements. They proposed a prompt (P) inventory of Fe production by an initial propulation with large Fe yields but little or no r production. This initial inventory ceased at [Fe/H]~-3, where the onset of high-frequency (H) events (SN II, tau~10^7 yrs) and low-frequency (L) events (SN Ia, tau~10^8yrs) initiated a correlation between r and Fe. Oh et al. (2001) pointed out that the trends in [Fe/H] and Ba also appear in Si and Ca, elements produced by PISN, but not in C, which is not abundantly produced by PISN, apparently strengthening the positive evidence that VMS dominated metal enrichment from the first stellar generation. Based on abundance patterns of extremely metal-poor Galactic stars: Oh et al. (2001), Qian & Wasserburg (2002): M>140 Msun PISN with no r-process elements Umeda & Nomoto (2004), Tumlinson, Venkatesan, & Shull (2004): M=10-140Msun Type II supernovae/hypernovae

Ionizing photon emission efficiency Pop III M*=10-300Msun: eUV=40,000-100,000 photons/baryon Salpeter IMF Z=0.01Zsun : eUV=3500 photons/baryon eUV(Pop III) /eUV(Pop II) =10-30 Bromm, Kudritzkl & Loeb (2001)

Existence of double peaks in h h = photon production rate/photon destruction rate = c* fesc (df*/dt) eUV/ C(1+z)3  Double peaks: one @z1~15-30, the other@z2~6-10 c*: star formation efficiency (unknown) fesc: ionizing photon escape fraction (unknown) eUV: ionizing photon production efficiency df*/dt: halo formation rate (computable) C: gas clumping factor (constrained)

A closer look: a pre-WMAP model Evolution of neutral hydrogen fraction Recent additional constraints: Wyithe & Loeb (2004): x=a few x 10% @z~6.3 based on QSO Stromgren sphere size Mesinger & Haiman (2004,ApJ): x>=0.2 @z~6.3 Haiman & Cen (2005,ApJ): x=<0.25 @z~6.5 based on LAE LF Malhotra & Rhoads (2004,ApJ): x<1 @z~6.5 White’s talk (2006): x~0.03 based on Stromgren sphere sizes. Totani’s talk (2006): X < 0.6 based on GRB spectra nHI/nHtot & nHII/nHtot XHI=0.1 – 0.3 @z=6-12 t=0.10 +- 0.03 Cen (2003a) Redshift

Evolution of the mean IGM temperature Mean IGM temperature (K) Redshift

Post-WMAP: implications on Pop III star formation processes Without Pop III massive stars: te < 0.09 With Pop III massive stars and reasonable star formation efficiency and ionizing photon escape fraction: te =0.09---0.12 With an inefficient metal enrichment process and Pop III massive stars: te = 0.15 possible To reach te = 0.17 requires either (1) ns >=1.03 or (2) c*(H2, III) > 0.01, or (3) photon escape fraction very high for Pop III Cen (2003b)

A more detailed calculation (Wyithe & Cen 2006, astro-ph/0602503) Separate treatments of halo gas and IGM in metal enrichment Follow Pop III/II with a gradual transition determined by metals Include photoionization feedback and minihalo screening effects fcrit/fJeans Redshift

New results from this more detailed calculation (Wyithe & Cen 2006) Without Pop III massive stars: te < 0.05-0.06, with a rapidly increasing xHI to >0.5 by z=8 With Pop III massive stars and reasonable star formation efficiency and ionizing photon escape fraction: te =0.09---0.12, with an extended plateau of xHI =0.1-0.3 at z=7-12 With perhaps too generous assumptions about Pop III star formation processes (very high escape fraction and/or very high star formation efficiency), te = 0.21 max is possible. Which one would I bet on? Physical sanity would eliminate the last choice. Physical reasonableness for Pop III IMF would then argue for the second choice. So te =0.09---0.12 seems most likely, same as I got 4 years ago. Judgement day: Thursday, March 16, 2006 (3rd Yr WMAP results)

A 24-billion-particle radiation transfer simulation of detailed cosmological reionization process (Trac & Cen 2006) Particle mass=2x106, Box size=100Mpc/h, timestep determined by c Ncell=120003, Spatial resolution=8kpc comoving

Ok, bets placed, that is all fine! But, How much do you REALLY know about first galaxies?

A 21-cm probe of individual first galaxies using CMB as the background radio source with an antenna temperature of TCMB dT = (Ts-TCMB)(1-e-t) TCMB = 85K, TIGM=18K @z=30

The structure of a first galaxy

Threshold by X-ray Background Heating Number per cubic Mpc Halo Mass

Brightness temperature decrement profile

Fundamental Applications with First Galaxies Probe IMF, ns, mCDM , … at n(gal)=1.e-6/Mpc3  Dns=0.01 (3s) Determine Pk: DV=100 Gpc3 within z=28-32 such as baryonic oscillations, etc., without messy astrophysical biases Alcock-Paczynski (AP) test: assuming each measurement 20% error, with 10,000 galaxies  Dw=0.012 (3s), if WM=0.3 (no error) and k=0

Abundance of 21-cm absorption halos Mean IGM temperature (K) Square arcseconds

Typical low high-z galaxies Theory: MHzG~108-109Msun Observed LAEs at z>6: SFR>40Msun/yr (Hu et al 2003; Kodaira et al 2003), assuming c*=0.10, tsb=5x107yrs ---> MLAE (total) = 1x1011Msun Thus, the current observations of z>6 LAEs do not probe the bulk of first galaxies; typical observed LAEs at z<6 have SFR~a few Msun/yr (Rhoads et al 2003; Taniguchi et al 2003) Cen (2003c)

Quasar Stromgren spheres Cen (2003c) Rs= 4.3x-1/3(N/1.3x1057s-1)1/3(tQ/2x107yr)1/3[(1+zQ)/7.28]-1 Mpc t(r)= 1.2x(WM/0.27)-1(Wb/0.047)[(Rs2-r2sin2q)1/2-r cosq]-1 , where Rs and r are in proper Mpc Cen & Haiman (2000)

(1): probing ionization state of IGM and sizes of Stromgren spheres Application of high-z galaxies inside quasar Stromgren spheres (1): probing ionization state of IGM and sizes of Stromgren spheres Evidently, (i) x=0.1 and x=0.01 differentiated at >6s level (ii) Rs determined to high accuracy; consequently, tQ determined accurately Rs=3Mpc Cen (2003) x=0.01 0.1 1.0 Rs=5Mpc

Application of first galaxies inside quasar Stromgren spheres, cont. (2) galaxy luminosity function and spatial distributions at z>6 (3) probing environment around quasars (4) probing anisotropy of quasar emission …

Conclusions The universe has a long reionization process (Wyithe & Cen 2006). The star formation processes at high-z may be quite different from those for low-z and local star formation 3rd+…… year WMAP data should give us a lot firmer information

A profitable way to detect high-z galaxies may be to target high-z observed luminous quasars, which provide a set of interesting applications Radio observations of 21-cm line may provide a unique way to detect the very first galaxies at z=30-40, which could potentially provide a set of fundamental applications.