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Ionization History of Hydrogen Signatures of the First Generation of Objects KITP 2004 Ionization History of Hydrogen REDSHIFT 6 1000 TIME Billion Million years years Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 1 Signatures of the First Generation of Objects Emergence of the First Star Clusters molecular hydrogen Yoshida et al. 2003 Hydrogen e- p Ground level excitation rate= (atomic collisions)+(radiative coupling to CMB) Couple T s to T k Couples T s to Tí spin 21cm = (1:4GHz) 1 1s 1=2 p e- 0s 1=2 p e- n 1 g1 0:068K Spin Temperature = expf à g (g1=g0) = 3 n 0 g0 Ts Predicted by Van de Hulst in 1944; Observed by Ewen &Purcell in 1951 at Harvard Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 2 Signatures of the First Generation of Objects 21 cm Absorption by Hydrogen Prior to Structure Formation à 1=2 à T = ü Ts Tí T = 28mK 1+ z Ts Tí b 1+ z b 10 Ts Fluctuations in 21cm brightness are sourced by fluctuations in gas density Loeb & Zaldarriaga, Phys. Rev. Lett., 2004; astro-ph/0312134 Observed wavelength=21cm (1+z) 3D tomography (slicing the universe in redshift ) Largest Data Set on the Sky Number of independent patches: 3 16 lmax É ÷ ø 10 106 ÷ while Silk damping limits the primary CMB anisotropies to only ø 107 Noise due to foreground sky brightness: Loeb & Zaldarriaga, Phys. Rev. Lett., 2004; astro-ph/0312134 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 3 Signatures of the First Generation of Objects Line-of-Sight Anisotropy of 21cm Flux Fluctuations à T = ü Ts Tí b 1+ z 1 + î n HI = nö(1 + î ) Peculiar velocity changes ü / 1 dvr =dr ø H(1 à 3î ) vr Power spectrum is not isotropic òk ~ dvr ! ~ 2 ~ k dr î v(k) = à cos òk â î (k) observer 2 ~ ~ 2 P Tb = [cos òkî (k) + î iso(k)] î iso = ì î + î x HI + î T + ::: 4 2 0 cos òk; cos òk; cos òk terms allow separation of powers Barkana & Loeb, astro-ph/0409572 Enhancement of 21cm Fluctuations During the Period of Initial Lya Coupling of the spin T to the kinetic T Wouthuysen-Field Effect 2P 3=2 P 1=2 T à T 1 3=2 1+ z s í P n=2 Tb = 28mK 10 T 1 1=2 s 0P 1=2 Lya Ts Tí ! Tb saturated 1s 1=2 21cm n=1 0s 1=2 Fluctuations in the distribution of galaxies induce fluctuations in Lya intensity 21cm ime ded t retar n in lutio d evo Rapi Barkana & Loeb, astro-ph/0410129 Lyì horizon Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 4 Signatures of the First Generation of Objects Enhancement of 21cm Fluctuations During the Epoch of Initial Lya Coupling Sourced by fluctuations in Power spectrum of 21cm Lya intensity from galaxies brightness fluctuations Biased fluctuations in the density of galaxies Poisson fluctuations in the number of galaxies Thermal History Temperature Tk Radiative coupling to CMB atomic collisions Ts Tí X-ray heating z=30 z=200 redshift Wouthuysen-Field Effect Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 5 Signatures of the First Generation of Objects History of 21cm Brightness Fluctuations • 30 < z < 200 HI appears in absorption against the CMB T < T with T < T < T • k cmb k s cmb 20 < z < 30 X-ray heating to à 3 Tk > Tcmb = 2 â 10 eV[(1 + z)=10] Lya coupling of spin temperature T s to kinetic temperature Tk HI appears in emission against the CMB • 6 < z < 20 Reionization: HI gradually disappears 21cm Tomography of Ionized Bubbles During Reionization is like Slicing Swiss Cheese H II H I Observed wavelength distance 21cm â (1 + z) Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 6 Signatures of the First Generation of Objects Experiments *MWA (Mileura Wide-Field Array) MIT/ATNF/CfA *LOFAR (Low-frequency Array) Netherlands *PAST (Primeval Structure Telescope) China/CITA *Enhanced VLA CfA/NRAO *SKA (Square Kilometer Array) When was the Universe Reionized? Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 7 Signatures of the First Generation of Objects Empirical Hints First Year Data from WMAP Polarization/temperature correlation implies an electron-scattering optical depth after cosmological recombination at z=1088 of: = 0:17 0:04 Implying that the universe was reionized at z = 17 5 Only 200 million years after the big bang Kogut et al. 2003 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 8 Signatures of the First Generation of Objects Cosmic Hydrogen was significantly Neutral at z~6.3 Ionization(Stromgren) Size of HII region sphere of quasar depends on line of sight neutral fraction of IGM prior to quasar activity and quasar age R(t) Wyithe & Loeb, Nature, 2004; astro-ph/0401188 The Earliest Quasar Detected: z=6.4 Fan et al. 2002 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 9 Signatures of the First Generation of Objects Likelihood for Neutral Fraction x H I at z~6.3 SDSS J1148+5251 7 ï (M + M ) 5=3 quasar lifetime = 4 â 10 f lt years 1 2 0:1 5=3 5=3 M 1 + M 2 Five quasars instead of two: P ! P 5=2 Imaging the Neutral Fraction in 21cm 21 cm Warm HI X-ray heated by quasar quasar reionization Lyë s s e Warm n t h CMB HI g i r B Cold HI wavelength 21 cm absorption of CMB if IGM is cold or 21 cm emission due to heating by X-ray background or quasar X-rays (but no Lyman-alpha heating by the quasar) ~100x relic shells per known quasar Wyithe and Loeb 2004; astro-ph/0401554 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 10 Signatures of the First Generation of Objects Emission from an X-ray Heated IGM Wyithe & Loeb 2004; astro-ph/0401554 The Characteristic Size of Ionized Bubbles at the End of Reionization Fig. 1 SBO: Surface of Bubble Overlap SLT: Surface of Lya Transmission Wyithe & Loeb, Nature, 2004 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 11 Signatures of the First Generation of Objects SDSS SLT quasars HI at z>6.1 photon • Causality: crossing time of bubble by a 21cm photon • . É t > R=c • Cosmic variance: cosmic scatter in the formation time of ionized bubbles due to large-scale inhomogeneities Does the Detection of Lya Emission from High-Redshift Galaxies Imply that the IGM Had Already Been Reionized? stars / unseen quasars galaxy / cluster of faint galaxies contributions of unseen sources Wyithe & Loeb, astro-ph/0407162 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 12 Signatures of the First Generation of Objects A Galaxy at a Redshift 10? Pello et al., 2004; astro-ph/0403025 But if it were, was the IGM Reionized at z=10? galaxy line-of-sight H+ • Neutral fraction <0.4 in the large-scale region around that galaxy, or galaxy harbors metal-free stars that create a sufficiently large HII region in IGM. • Lya damping wing from outside Stromgren sphere allows Lya line transmission. • Resonant absorption inside Stromgren sphere may be suppressed by peculiar velocity relative to IGM. Loeb, Barkana, & Hernquist 2004; astro-ph/0403193 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 13 Signatures of the First Generation of Objects Theoretical Insights (i) Should we trust numerical simulations or analytic models? Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 14 Signatures of the First Generation of Objects Cooling Rate of Primordial Gas n=0.045 cm^-3 Atomic cooling H_2 cooling Virial Temperature of Halos Atomic cooling H_2 cooling 3-sigma 1-sigma 2-sigma Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 15 Signatures of the First Generation of Objects Unusually Large Fluctuations in the Statistics of Galaxy Formation at High Redshifts Bias in numerical simulations: L Assumption : î L = 0 Barkana & Loeb, ApJ, 2003; astro-ph/0310338 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 16 Signatures of the First Generation of Objects (ii) Was Reionization Caused by Metal-Free or Metal-Rich Stars? Massive Accretion by Pop-III Proto-Stars 23.5pc 0.5pc Resolving accretion flow down to ~0.03 pc Bromm & Loeb, New Astronomy, 2004; astro-ph/0312456 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 17 Signatures of the First Generation of Objects Number of ionizing photons (>13.6eV) per baryon incorporated into stars: Massive, metal free stars M > 300M ì 100; 000 M > 100M ì 40; 000 5 Teff ø 10 K L = L E / M Gain by up to a factor of ~30! Metal free 7; 000 Salpeter mass function Z = 0:01Z ì 3; 500 Bromm, Kudritzki, & Loeb 2001, ApJ, 552, 464 SPH Simulation of a Hypernova Explosion 53 51 E SN = 10 ergs; E vir = 10 ergs 1kpc Bromm, Yoshida, & Hernquist 2003 Avi Loeb, Harvard (KITP Galaxy-IGM Conference 10/26/04) 18 Signatures of the First Generation of Objects Minimum Carbon and Oxygen Abundance Required for the Formation of Low-Mass Stars Lines: t cooling < t collapse Cooling rate by C II or O I allows fragmentation in metal-poor gas clumps Filled points: halo dwarf stars Open squares: giant stars n ø 104 cm à 3 T 100 200 K M J 100M ì Bromm & Loeb, Nature, 2003; astro-ph/0310622 Reionization Histories of H, He Free Parameters: (i) transition redshift, z_ttran , above which the stellar IMF is dominated by massive, zero-metallicity stars; (ii) the product of the star formation efficiency and the escape fraction of ionizing photons in galaxies, f e s c f ? .
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