LARS XIII: High Angular Resolution 21 cm H i Observations of Lyα Emitting Galaxies

Abstract

The Lyα emission line is one of the main observables of galaxies at high redshift, but its output depends strongly on the neutral gas distribution and kinematics around the star-forming regions where UV photons are produced. We present observations of Lyα and 21 cm H i emission at comparable scales with the goal to qualitatively investigate how the neutral interstellar medium (ISM) properties impact Lyα transfer in galaxies. We have observed 21 cm H i at the highest possible angular resolution (≈3″ beam) with the Very Large Array in two local galaxies from the Lyman Alpha Reference Sample. We compare these data with Hubble Space Telescope Lyα imaging and spectroscopy, and Multi Unit Spectroscopic Explorer and Potsdam MultiAperture Spectrophotometer ionized gas observations. In LARS08, high-intensity Lyα emission is cospatial with high column density H i where the dust content is the lowest. The Lyα line is strongly redshifted, consistent with a velocity redistribution that allows Lyα escape from a high column density neutral medium with a low dust content. In eLARS01, high-intensity Lyα emission is located in regions of low column density H i, below the H i data sensitivity limit ( < 2 × 1020 cm−2). The perturbed ISM distribution with low column density gas in front of the Lyα emission region plays an important role in the escape. In both galaxies, the faint Lyα emission (∼1×10−16 erg s−1cm−2 arcsec−2) traces intermediate Hα emission regions where H i is found, regardless of the dust content. Dust seems to modulate, but not prevent, the formation of a faint Lyα halo. This study suggests the existence of scaling relations between dust, Hα, H i, and Lyα emission in galaxies.