The Lyα Reference Sample. XIV. Lyα Imaging of 45 Low-redshift Star-forming Galaxies and Inferences on Global Emission

Abstract

We present Ly α imaging of 45 low-redshift star-forming galaxies observed with the Hubble Space Telescope. The galaxies have been selected to have moderate to high star formation rates (SFRs) using far-ultraviolet (FUV) luminosity and H α equivalent width criteria, but no constraints on Ly α luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Ly α , H α , and H β maps. We find that Ly α is less concentrated than FUV and optical line emission in almost all galaxies with significant Ly α emission. We present global measurements of Ly α and other quantities measured in apertures designed to capture all of the Ly α emission. We then show how the escape fraction of Ly α relates to a number of other measured quantities (mass, metallicity, star formation, ionization parameter, and extinction). We find that the escape fraction is strongly anticorrelated with nebular and stellar extinction, weakly anticorrelated with stellar mass, but no conclusive evidence for correlations with other quantities. We show that Ly α escape fractions are inconsistent with common dust extinction laws, and discuss how a combination of radiative transfer effects and clumpy dust models can help resolve the discrepancies. We present an SFR calibration based on Ly α luminosity, where the equivalent width of Ly α is used to correct for nonunity escape fraction, and show that this relation provides a reasonably accurate SFR estimate. We also show stacked growth curves of Ly α for the galaxies that can be used to find aperture loss fractions at a given physical radius.