Ultraviolet Pumping of the 21-cm Line in the High Redshift Universe Leonid Chuzhoy University of Texas at Austin Collaborators: Marcelo Alvarez (Stanford), Paul R. Shapiro (UT), Zheng Zheng (IAS)

21 cm transition T s <T CMB T s >T CMB Absorption Emission

Upcoming radio observations LOFAR: partial array full array SKA: partial array full array CMA/PAST: complete(?) MWA: partial array

What can we learn from 21 cm continuum? The reionization history of the universe (e.g. Madau, Meiksin & Rees 1997; Ciardi & Madau 2003) Cosmological parameters: H(z), Ω b,, Ω m,, n (e.g. Loeb & Zaldarriaga 2004; Nusser 2005; Santos & Cooray 2006; McQuinn et al. 2005) The nature of the first radiation sources (Barkana & Loeb 2005; Chuzhoy, Alvarez & Shapiro 2006; Pritchard & Furlanetto 2006) Primordial magnetic field strength (Tashiro & Sugiyama 2006) Physical properties of dark matter particles (Shchekinov & Vasiliev 2006; Furlanetto et al. 2006) Variation in the fine structure constant (Khatri & Wandelt 2007)

TsTs TαTα TkTk T cmb Atomic collisions UV resonance photons CMB photons

Energy levels of hydrogenic atoms (H, D, 3 He+) 21/92/3.4 cm 1s 2p 3p Lyα Lyβ

Wouthuysen-Field mechanism (Wouthuysen 1952; Field 1959) H

Sources of Lyα photons – UV continuum (Lyα to Lyβ)

Scattering of high resonance photons (Lyβ to Ly-limit) n=1 Lyγ Lyα HβHβ

Scattering rate vs radius (C & Zheng 2007) “continuum” Lyα photons

Central asymptote “Continuum” Lyα photons “Injected” Lyα photons

Photon spectrum around Lyα resonance – “continuum” photons

Photon spectrum around Lyα resonance - “injected” photons

Intensity variation of Lyα photons (Chen & Miralda-Escude 2004; Hirata 2006; C & Shapiro 2006a; Rybicki 2006) In the expanding region the radiation intensity around the resonance falls by a factor: For unperturbed Hubble flow:

Revised Wouthuysen-Field mechanism ( Hirata 2006; C & Shapiro 2006a ) T cmb TsTs TαTα TkTk

Color temperature of Lyα photons (Hirata 2006; C & Shapiro 2006a) Average energy gain of Lyα photon in a single scattering:

Heating of IGM by Lyα photons – Atomic Recoil (Madau, Meiksin & Rees 1997) H By the time UV resonance photons decouple T s from T CMB, the gas temperature rises above T CMB (i.e. the absorption epoch is suppressed).

Heating of IGM by Lyα photons – Thermal motion (Chen & Miralda-Escude 2004) H

Photon spectrum around Lyα resonance – “continuum” photons

Photon spectrum around Lyα resonance - “injected” photons

Heating vs Cooling Gas heating rate by continuum Lyα photons drops with increasing temperature, while cooling rate by injected photons rises. T k <~ 10 K Resonance photons can not move the 21-cm signal from absorption to emission.

Scattering of high resonance photons – cascade via 2s state 1s 2p,2s

Heating of IGM by D Lyβ photons (C & Shapiro 2006b)

Heating of IGM by resonance photons Deuterium is thermally decoupled from hydrogen and may be heated up to K. Deuterium spin temperature is negative. The relative strength of hydrogen and deuterium lines does not reflect the abundance ratio. Hydrogen and helium atoms are collisionally heated by deuterium atoms up to ~300 K. This entropy increase leads to partial suppression of minihalos. Hydrogen kinetic temperature rises above T CMB only after its spin temperature is decoupled (i.e., the absorption is not suppressed).

21 cm emission from partially ionized gas (e.g. Gnedin & Shaver 04; Kuhlen, Madau & Montgomery 06)

Lyα

Sources of Lyα photons – X-rays (C, Alvarez & Shapiro 2006)

Sources of Lyα photons – Recombining HII regions

Sources of Lyα photons – Superwinds