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

We present Ly alpha 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 alpha equivalent width criteria, but no constraints on Ly alpha luminosity. We employ a pixel stellar continuum fitting code to obtain accurate continuum-subtracted Ly alpha, H alpha, and H beta maps. We find that Ly alpha is less concentrated than FUV and optical line emission in almost all galaxies with significant Ly alpha emission. We present global measurements of Ly alpha and other quantities measured in apertures designed to capture all of the Ly alpha emission. We then show how the escape fraction of Ly alpha 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 alpha 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 alpha luminosity, where the equivalent width of Ly alpha 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 alpha for the galaxies that can be used to find aperture loss fractions at a given physical radius.