Inferring population III star properties from the 21-cm global signal

Abstract

Investigating the properties of the first stars in the universe is essential, yet it remains an open question. One way to explore these stars is by examining their effects on the surrounding gas during the epoch of reionization. In this study, we investigate whether the 21-cm global signal can constrain the typical mass and star formation efficiency of first-generation stars. We perform semi-numerical simulations that include the escape fraction of ionizing photons, which depends on stellar and halo masses, as well as the heating structure surrounding a halo that hosts the first star, determined by radiation hydrodynamics (RHD) simulations. By applying Fisher analysis, while accounting for foreground emissions, we demonstrate that future observations with instruments such as the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH) could provide meaningful constraints on these properties.

Figures (12)

• Figure 1: Escape fraction–halo mass relation. Relationship between the ionizing photon escape fraction, $\mathscr{f}\mathrm{esc}$, and halo mass, $M_\mathrm{h}$, shown for several stellar masses, $M_\mathrm{s}$. $\mathscr{f}_\mathrm{esc}$ decreases with increasing $M_\mathrm{h}$ due to enhanced absorption by hydrogen within more massive haloes, while it increases with increasing $M_\mathrm{s}$ as stronger ionizing emission drives faster expansion of the ionized bubble inside the halo.
• Figure 2: Halo-mass-averaged escape fraction $f_\mathrm{esc}$ as a function of the threshold halo mass for star formation $M_\mathrm{cool}$ in the case of $M_{\rm s}=200 M_\odot$. The escape fraction $f_\mathrm{esc}$ decreases with increasing $M_\mathrm{cool}$ because star formation becomes restricted to more massive haloes that individually exhibit smaller escape fractions, $\mathscr{f}_\mathrm{esc}$. It declines toward lower redshifts, reflecting the increasing contribution of massive haloes that form preferentially at later times.
• Figure 3: The global 21-cm brightness temperatures as functions of redshift. The solid, dashed and dotted lines are cases of $f_* = 0.1, 0.01, 0.001$ respectively. The red, green, blue lines are cases of $M_\mathrm{s} = 500, 200, 120 \,\mathrm{M_\odot}$ respectively.
• Figure 4: The star formation rate density as a function of redshift. The line styles and colors correspond to the same parameter values as Figure \ref{['fig:Tb']}.
• Figure 5: The halo-mass-averaged escape fraction give by eq. \ref{['eq:averaged_fesc']} as a function of redshift. The line styles and colors correspond to the same parameter values as Figure \ref{['fig:Tb']}.