The Lyman Alpha Reference Sample

Context. The Lyman- α (Ly α ) line of hydrogen is a well-known tracer of galaxies at high redshift. However, the connection between Ly α observables and galaxy properties has not been fully established, limiting the use of the line to probe the physics of galaxies. Aims. Here, we derive the global neutral hydrogen gas (H I ) properties of nearby Ly α -emitting galaxies to assess the impact of neutral gas on the Ly α output of galaxies. Methods. We observed the 21 cm line emission using the Karl G. Jansky Very Large Array in D-array configuration (∼55″ resolution, ∼38 kpc) for 37 star-forming galaxies with available Hubble Space Telescope (HST) Ly α imaging from the Lyman Alpha Reference Samples. Results. We detected 21 cm emission for 33 out of the 37 galaxies observed. We found no significant correlation of global H I properties (including H I mass, column density, gas fraction, depletion time, line width, or velocity shift between H I and Ly α ), with the Ly α luminosity, escape fractions, or equivalent widths (EW) derived with HST photometry. Additionally, both Ly α -emitters and weak or non-emitters are distributed evenly along the H I parameter space of optically selected z = 0 galaxies. Around 74% of the sample is undergoing galaxy interaction, this fraction is higher for Ly α -emitters (83% for galaxies with EW ≥ 20 Å) than for weak or non-emitters (70%). Nevertheless, galaxies identified as interacting have Ly α and H I properties statistically consistent with those of non-interacting galaxies. Conclusions. Our results show that global H I properties (on scales > 30kpc) have little direct impact on the Ly α output from galaxies. Instead, H I likely regulates Ly α emission on small scales: statistical comparisons of Ly α and high angular resolution 21 cm observations are required to fully assess the role of H I in Ly α radiative transfer. While our study indicates that major and minor galaxy mergers could play a role in the emission of Ly α photons in the Local Universe, especially for galaxies with high H I fractions, the line of sight that a system is observed through ultimately determines the Ly α observables.