EDGE: What shapes the relationship between H i and stellar observables in faint dwarf galaxies?

We show how the interplay between feedback and mass-growth histories introduces scatter in the relationship between stellar and neutral gas properties of field faint dwarf galaxies (M-*less than or similar to 10(6) M-circle dot). Across a suite of cosmological, high-resolution zoomed simulations, we find that dwarf galaxies of stellar masses 10(5) <= M-* <= 106 M-circle dot are bimodal in their cold gas content, being either H I-rich or H I-deficient. This bimodality is generated through the coupling between (i) the modulation of H I contents by the background of ultraviolet radiation (UVB) at late times and (ii) the significant scatter in the stellar-to-halo mass relationship induced by reionization. Furthermore, our H I-rich dwarfs exhibit disturbed and time-variable neutral gas distributions primarily due to stellar feedback. Over the last four billion years, we observe order-of-magnitude changes around the median M-H I, factor-of-a-few variations in H I spatial extents, and spatial offsets between H I and stellar components regularly exceeding the galaxies' optical sizes. Time variability introduces further scatter in the M-*-M-H I relation and affects a galaxy's detectability in H I at any given time. These effects will need to be accounted for when interpreting observations of the population of faint, H I-bearing dwarfs by the combination of optical and radio wide, deep surveys.

Automated summary

The interplay between feedback and mass-growth histories introduces scatter in the relationship between stellar and neutral gas properties of faint dwarf galaxies. Simulations show that dwarf galaxies with stellar masses between 10^5 to 10^6 solar masses exhibit bimodality in their cold gas content, either being H I-rich or H I-deficient. Stellar feedback plays a significant role in creating disturbed and time-variable neutral gas distributions.