Day 476

Monday.

1307.6859
Lyman-alpha heating of inhomogeneous high-redshift intergalactic medium
Oklopcic, Hirata

IGM before reionization consists mostly of neutral H gas.  Ly-a photons produced by early stars resonantly scatter off H atoms, causing energy exchange between the radiation field and the gas.  This interaction results in moderate heating of the gas due to the recoil of the atoms upon scattering, which is of great interest for future studies of the pre-reionzation IGM in the HI 21 cm line.  Investigate the effect of the Ly-a heating in the IGM with linear density, temperature and velocity perturbations.  Perturbations smaller than the diffusion length of photons could be damped due to heat conduction by Ly-a photons.  The scale at which damping occurs and the strength of this effect depend on various properties of the gas, the flux of Ly-a photons and the way in which photon frequencies are redistribtued upon scattering.  To find the relevant length scale and the extent to which Ly-a heating affects perturbations, calculate the gas heating rates by numerically solving linearized Boltzmann equations in which scattering is treated by the Fokker-Planck approximation.  Find that (i) perturbations add a small correction to the gas heating rate, and (ii) the damping of temperature perturbations occurs at scales with comoving wavenumber K>1d4 Mpc^-1, which are much smaller than the Jeans scale and thus unlikely to substantially affect the observed 21 cm signal.