21-cm signature of the first sources in the Universe: Prospects of detection with SKA

TL;DR

This paper models the 21-cm signal around early cosmic sources and assesses their detectability with SKA1-low, finding potential for significant detection of first sources like galaxies and quasars at high redshift.

Contribution

It introduces detailed radiative transfer simulations of the 21-cm signal around various first sources and evaluates their detectability with SKA1-low, providing scaling laws for SNR estimation.

Findings

Potential to detect isolated first sources at z~15 with 9-sigma significance in 1000 hours

Detection feasibility decreases with increasing redshift due to lower SNR

Foreground subtraction techniques can preserve detection sensitivity

Abstract

Currently several low-frequency experiments are being planned to study the nature of the first stars using the redshifted 21-cm signal from the cosmic dawn and epoch of reionization. Using a one-dimensional radiative transfer code, we model the 21-cm signal pattern around the early sources for different source models, i.e., the metal-free Population III (PopIII) stars, primordial galaxies consisting of Population II (PopII) stars, mini-QSOs and high-mass X-ray binaries (HMXBs). We investigate the detectability of these sources by comparing the 21-cm visibility signal with the system noise appropriate for a telescope like the SKA1-low. Upon integrating the visibility around a typical source over all baselines and over a frequency interval of 16 MHz, we find that it will be possible to make a $\sim 9-\sigma$ detection of the isolated sources like PopII galaxies, mini-QSOs and HMXBs at $z \sim 15$ with the SKA1-low in 1000 hours. The exact value of the signal to noise ratio (SNR) will depend on the source properties, in particular on the mass and age of the source and the escape fraction of ionizing photons. The predicted SNR decreases with increasing redshift. We provide simple scaling laws to estimate the SNR for different values of the parameters which characterize the source and the surrounding medium. We also argue that it will be possible to achieve a SNR $\sim 9$ even in the presence of the astrophysical foregrounds by subtracting out the frequency-independent component of the observed signal. These calculations will be useful in planning 21-cm observations to detect the first sources.