Searching for the earliest galaxies in the 21 cm forest

TL;DR

This paper models 21 cm absorption signatures from early galaxies and minihalos to develop criteria for identifying high-redshift galaxies, aiding future observations with JWST.

Contribution

It introduces a statistical method to select candidate dwarf galaxies and minihalos at redshifts above 8 using 21 cm line absorption features.

Findings

Approximately 18% of dwarf galaxies can be identified by W_ u < 0.

About 11% of minihalos are selected with W_ u > 0.37 kHz.

Selected galaxies are embedded in large HII regions, facilitating future IR observations.

Abstract

We use a model developed by Xu et al. (2010) to compute the 21 cm line absorption signatures imprinted by star-forming dwarf galaxies (DGs) and starless minihalos (MHs). The method, based on a statistical comparison of the equivalent width (W_\nu) distribution and flux correlation function, allows us to derive a simple selection criteria for candidate DGs at very high (z >= 8) redshift. We find that ~ 18% of the total number of DGs along a line of sight to a target radio source (GRB or quasar) can be identified by the condition W_\nu < 0; these objects correspond to the high-mass tail of the DG distribution at high redshift, and are embedded in large HII regions. The criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs could later be re-observed in the near-IR by the JWST with high efficiency, thus providing a direct probe of the most likely reionization sources.