STScI, Feb. 27, 2004

Exploring Early Structure Formation with a Very Large Space Telecope Avi Loeb Harvard University Avi Loeb Harvard University

Cosmic-Archeology : the First Stars and The Reionization on the Universe The more distant a source is, the more time it takes for its light to reach us. Hence the light must have been emitted when the universe was younger. By looking at distant sources we can trace the history of the universe. distance Earth

First Year Data from WMAP Polarization/temperature correlation implies an electron-scattering optical depth after cosmological recombination at z=1088 of: Implying that the universe was reionized at Only 200 million years after the big bang Kogut et al. 2003

Cosmic Hydrogen was significantly Neutral at z~6.3 Wyithe & Loeb, Nature, 2004; astro-ph/ Size of HII region depends on neutral fraction of IGM prior to quasar activity and quasar age Ionization(Stromgren) sphere of quasar line of sight R(t)

Likelihood for Neutral Fraction at z~6.3 SDSS J

But on small scales the universe is clumpy Mean Density Early times Intermediate times Late times

Ionization History of Hydrogen REDSHIFT TIME Million years Billion years

Emergence of the First Star Clusters molecular hydrogen Yoshida et al. 2003

Astronomy of the Early Universe When did the first stars and quasars form? When was the universe re-ionized? How quickly was the intergalactic medium enriched with metals from the first stars? Most pressing questions:

Metal-Free Stars were massive: Simulations Bromm, Coppi, & Larson 2000 ~1 kpc ~ 2500 A.U. Abel, Bryan, & Norman 2000

Spectrum of Pop-III Stars ---> unusually strong recombination lines (H_alpha) Bromm, Kudritzki, & Loeb 2001

Formation of Massive Black Holes in the First Galaxies Add Bromm Low-spin systems: Eisenstein & Loeb 1995 Numerical simulations: Bromm & Loeb 2002

Supermassive Stars For a spherical (non-rotating) star: general-relativistic instability at Angular momentum mass shedding along equator Collapse to a black hole is inevitable for

Why a Very Large Space Telescope? Probe rest-frame UV emission at z=6-10. NIR capability is essential: Identify the galaxies that dominate the ionizing background during reionization Use UV spectra to infer the dominant stellar population during reionization (and gauge the role of massive, metal-poor, Pop-III stars) Find faint quasars and reveal the emergence of quasar seeds

Number of ionizing photons (>13.6eV) per baryon incorporated into stars : Massive, metal free stars Salpeter mass function Bromm, Kudritzki, & Loeb 2001, ApJ, 552, 464 Metal free Gain by up to a factor of ~30!

Cooling Rate of Primordial Gas n=0.045 cm^-3 Atomic cooling H_2 cooling

Virial Temperature of Halos 1-sigma2-sigma 3-sigma Atomic cooling H_2 cooling

Reviews on the physics of reionization: *Barkana & Loeb 2001, Physics Reports 349, 125 *Loeb & Barkana 2001, Ann.Rev.Ast.&Ap, 39, sigma 2-sigma 3-sigma Atomic cooling H_2 cooling 2-sigma Collapse Redshift of Halos

Why should VLST have High Resolution?

Virial Radius of Halos 1-sigma2-sigma3-sigma

Why should VLST have a Wide Field?

Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshifts Barkana & Loeb 2003 (astro-ph/ ) L Bias in numerical simulations:

Exploring the Time Domain with VLST: The High-Redshift Universe Can be Best Probed Through Transient Events Gamma-Ray Burst afterglows [days x (1+z)] Supernovae [weeks x (1+z)] Quasars [Myr x (1+z)]

Binding Energy of Dark Matter Halos 1-sigma2-sigma 3-sigma Supernova

Self-Regulated Star Formation Virial temperature < 10,000K destruction by starlight (10.2<E<13.6 eV) Evaporation of gas cloud by photo-ionization heating to >10,000K As observed for local dwarf galaxies in SDSS (Kaufmann et al. 2002) Virial temperature > 10,000K (Dekel & Silk)

Bromm, Yoshida, & Hernquist 2003 SPH Simulation of a Hypernova Explosion 1kpc

Pair-Instability Supernova

Minimum Carbon and Oxygen Abundance Required for the Formation of Low-Mass Stars Lines: Cooling rate by C II or O I allows fragmentation in metal-poor gas clumps Filled points: halo dwarf stars Open squares: giant stars Bromm & Loeb 2003, Nature, in press

Self-regulation of Supermassive Black Hole Growth quasar dynamical time of galactic disk halo velocity dispersion After translating this relation matches the observed correlation in nearby galaxies (Tremaine et al. 2002; Ferarrese & Merritt 2002) Silk &Rees 1998; Wyithe & Loeb 2003

Quasar Luminosity Function Wyithe & Loeb 2002 Simple physical model: *Each galaxy merger leads to a bright quasar phase during which the black hole grows to a mass and shines at the Eddington limit. The duration of this bright phase is proportional to the (smaller than unity) mass ratio in the merger. *Merger rate: based on the extended Press-Schechter model in a LCDM cosmology. duty cycle ~10 Myr

The Earliest Quasar Detected: z=6.43 Fan et al. 2002

Gamma-Ray Bursts: Probing one Star at a Time Gamma-Ray Bursts: Probing one Star at a Time Progenitors NS Collapse of a Massive Star (possibly leading to a supernova) Coalescence of NS/NS or NS/BH Binaries In both cases the original progenitors are massive stars (which should exist at high redshifts)

Detectability of Afterglow Emission Near the Lya Wavelength Photometric redshift identification: based on the Lya trough z=15 z=5 z=11 z=7z=9 JWST sensitivity Barkana & Loeb 2003 astro-ph/

Weak contamination by Lya emission line Gamma-Ray Burst AfterglowsQuasars GRB Infall onto Massive Host Galaxy Ionized Gas flux wavelength Lyman-alpha Damping Wing Quasars get fainter with increasing redshift because galaxies are less massive and the luminosity distance increases at higher redshifts!

Advantages of GRB Afterglows Relative to Quasars (see details in astro-ph/ ) Luminous stellar sources high redshifts –outshine galaxies and quasars, as they become less luminous at increasingly higher redshifts – -ray trigger allows all-sky monitoring Featureless broad-band spectra extending into the rest-frame UV –absorption features can be used to probe the ionization and metallicity states of the IGM Observed flux at a fixed observed age does not fade significantly with increasing GRB redshift (cosmological time stretching counteracts increase in luminosity distance) Weak Feedback on Surrounding IGM - Short-lived event: negligible ionizing effect of a GRB on the IGM -Low mass host galaxies: weak IGM infall & Lya line emission