Detecting Early Galaxies Through Their 21-cm Signature

TL;DR

This paper predicts the 21-cm signal signature of early galaxies, incorporating new physical effects, to aid future observations in detecting galaxies formed 200 million years after the Big Bang.

Contribution

It introduces a refined model of the 21-cm power spectrum including photon scattering and ionized bubbles, enhancing detection prospects of early galaxies.

Findings

Enhanced 21-cm signal due to photon scattering

Presence of ionized bubbles causes a cutoff in the spectrum

Detectable signature of galaxies formed 200 million years post-Big Bang

Abstract

New observations over the next few years of the emission of distant objects will help unfold the chapter in cosmic history around the era of the first galaxies. These observations will use the neutral hydrogen emission or absorption at a wavelength of 21-cm as a detector of the hydrogen abundance. We predict the signature on the 21-cm signal of the early generations of galaxies. We calculate the 21-cm power spectrum including two physical effects that were neglected in previous calculations. The first is the redistribution of the UV photons from the first galaxies due to their scattering off of the neutral hydrogen, which results in an enhancement of the 21-cm signal. The second is the presence of an ionized hydrogen bubble near each source, which produces a cutoff at observable scales. We show that the resulting clear signature in the 21-cm power spectrum can be used to detect and study the population of galaxies that formed just 200 million years after the Big Bang.