Where are All the Gas-Bearing Local Dwarf Galaxies? Quantifying Possible Impacts of Reionization

TL;DR

This study compares Local Group dwarf galaxy detections in HI surveys with simulations, revealing a discrepancy that can be explained by reionization effects preventing gas formation in low-mass halos, thus constraining the impact scale.

Contribution

The paper introduces an empirical method to compare observations and simulations of dwarf galaxies, highlighting the role of reionization in suppressing gas in low-mass halos.

Findings

No LG dwarfs detected in HI survey, but simulations predict ~10.

Reionization can explain the lack of gas in low-mass halos.

Reionization impacts dwarf galaxy gas content at ~10^{8.5} solar masses.

Abstract

We present an approach for comparing the detections and non-detections of Local Group (LG) dwarf galaxies in large HI surveys to the predictions of a suite of n-body simulations of the LG. This approach depends primarily on a set of empirical scaling relations to connect the simulations to the observations, rather than making strong theoretical assumptions. We then apply this methodology to the Galactic Arecibo L-band Feed Array HI Compact Cloud Catalog (GALFA-HI CCC), and compare it to the ELVIS suite of simulations. This approach reveals a strong tension between the na\"ive results of the model and the observations: while there are no LG dwarfs in the GALFA-HI CCC, the simulations predict $\sim 10$. Applying a simple model of reionization can resolve this tension by preventing low-mass halos from forming gas. However, and if this effect operates as expected, the observations provide a constraint on the mass scale of dwarf galaxy that reionization impacts. Combined with the observed properties of Leo T, the halo virial mass scale at which reionization impacts dwarf galaxy gas content is constrained to be $\sim 10^{8.5} M_\odot$, independent of any assumptions about star formation.