Lyalpha heating and its impact on early structure formation

TL;DR

This study investigates how Lyalpha photons from the first stars heat the intergalactic medium, influencing early structure formation, gas clumping, and the 21cm signal, with implications for understanding the epoch of reionization.

Contribution

It provides the first detailed calculation of Lyalpha heating effects on IGM temperature and structure formation for different stellar initial mass functions.

Findings

Lyalpha photons heat the IGM to ~100 K at z<25.

Lyalpha heating reduces gas fraction in small halos below 5 x 10^6 M_sun.

Heating makes the 21cm line visible in emission at z<15.

Abstract

In this paper we have calculated the effect of Lyalpha photons emitted by the first stars on the evolution of the IGM temperature. We have considered both a standard Salpeter IMF and a delta-function IMF for very massive stars with mass 300 M_sun. We find that the Lyalpha photons produced by the stellar populations considered here are able to heat the IGM at z<25, although never above ~100 K. Stars with a Salpeter IMF are more effective as, due to the contribution from small-mass long-living stars, they produce a higher Lyalpha background. Lyalpha heating can affect the subsequent formation of small mass objects by producing an entropy floor that may limit the amount of gas able to collapse and reduce the gas clumping.We find that the gas fraction in halos of mass below ~ 5 x 10^6 M_sun is less than 50% (for the smallest masses this fraction drops to 1% or less) compared to a case without Lyalpha heating. Finally, Lyalpha photons heat the IGM temperature above the CMB temperature and render the 21cm line from neutral hydrogen visible in emission at z<15.