Imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA

TL;DR

This paper explores the feasibility of imaging the 21-cm signal from the first sources during cosmic dawn using SKA1-low, demonstrating that with foreground subtraction and smoothing, these sources can be detected at high confidence levels in realistic simulations.

Contribution

The study models 21-cm images around first sources during cosmic dawn, incorporating astrophysical foregrounds and overlaps, and assesses their detectability with SKA1-low.

Findings

Sources at z ~ 15 detectable with 4-9 sigma in 2000 hours.

Foreground subtraction and smoothing enable source detection.

Multiple short observations can identify promising fields for longer integration.

Abstract

Understanding properties of the first sources in the Universe using the redshifted \HI ~21-cm signal is one of the major aims of present and upcoming low-frequency experiments. We investigate the possibility of imaging the redshifted 21-cm pattern around the first sources during the cosmic dawn using the SKA1-low. We model the \HI ~21-cm image maps, appropriate for the SKA1-low, around the first sources consisting of stars and X-ray sources within galaxies. In addition to the system noise, we account also for the astrophysical foregrounds by adding them to the signal maps. We find that after subtracting the foregrounds using a polynomial fit and suppressing the noise by smoothing the maps over $10^{'} - 30^{'}$ angular scale, the isolated sources at $z \sim 15$ are detectable with $\sim 4 - 9 \, \sigma$ confidence level in 2000 h of observation with the SKA1-low. Although the 21-cm profiles around the sources get altered because of the Gaussian smoothing, the images can still be used to extract some of the source properties. We account for overlaps in the patterns of the individual sources by generating realistic \HI ~21-cm maps of the cosmic dawn that are based on $N$-body simulations and a one-dimensional radiative transfer code. We find that these sources should be detectable in the SKA1-low images at $z = 15$ with an SNR of $\sim 14 (4)$ in 2000 (200) h of observations. One possible observational strategy thus could be to observe multiple fields for shorter observation times, identify fields with SNR $\gtrsim 3$ and observe these fields for much longer duration. Such observations are expected to be useful in constraining the parameters related to the first sources.