Spatially Extended 21 cm Signal from Strongly Clustered UV and X-Ray Sources in the Early Universe

TL;DR

This study predicts the spatially extended 21 cm signal from highly clustered early universe sources, highlighting their detectability and the impact of UV and X-ray feedback on the intergalactic medium.

Contribution

It introduces a detailed simulation of the 21 cm signal from rare, high-density peaks with clustered Pop III and II sources, emphasizing the role of X-ray feedback and environment in shaping the signal.

Findings

Rarepeak is detectable as a single extended 21 cm source by SKA.

High-density environments amplify the 21 cm signal, making it distinguishable.

Power spectrum analysis of rare peaks is challenging due to their rarity.

Abstract

We present our prediction for the local 21 cm differential brightness temperature ($\delta T_{b}$) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early Universe, by a numerical simulation of their formation and radiative feedback. These objects are located inside a highly biased environment, which is a rare, high-density peak ("Rarepeak") extending to $\sim7$ comoving Mpc. We study the impact of ultraviolet (UV) and X-ray photons on the intergalactic medium (IGM) and the resulting $\delta T_{b}$, when Pop III stars are assumed to emit X-ray photons by forming X-ray binaries very efficiently. We parameterize the rest-frame spectral energy distribution (SED) of X-ray photons, which regulates X-ray photon-trapping, IGM-heating, secondary Lyman-alpha pumping and the resulting morphology of $\delta T_{b}$. A combination of emission ($\delta T_{b}>0$) and absorption ($\delta T_{b}<0$) regions appears in varying amplitudes and angular scales. The boost of the signal by the high-density environment ($\delta\sim0.64$) and on a relatively large scale combine to make Rarepeak a discernible, spatially-extended ($\theta\sim10'$) object for 21 cm observation at $13\lesssim z\lesssim17$, which is found to be detectable as a single object by SKA with integration time of $\sim1000$ hours. Power spectrum analysis by some of the SKA precursors (LOFAR, MWA, PAPER) of such rare peaks is found difficult due to the rarity of these peaks, and the contribution only by these rare peaks to the total power spectrum remains subdominant compared to that by all astrophysical sources.