The Lyman alpha Reference Sample: II. HST imaging results, integrated properties and trends

TL;DR

This study analyzes HST imaging of 14 galaxies from the Lyman alpha Reference Sample, revealing how Lya emission profiles differ from UV, and identifying properties that influence Lya escape, with implications for high-redshift galaxy observations.

Contribution

It provides detailed Lya, Halpha, and UV imaging data, and uncovers correlations between Lya escape and galaxy properties, offering new insights into low-z analogs of high-z Lya emitters.

Findings

Lya profiles are less centrally concentrated than UV profiles.

Flux and EW curves flatten at ~10 kpc, indicating limited flux loss at high z.

Some galaxies exhibit high Lya EWs and escape fractions, previously unreported at low z.

Abstract

We report upon new results regarding the Lya output of galaxies, derived from the Lyman alpha Reference Sample (LARS), focusing on Hubble Space Telescope imaging. For 14 galaxies we present intensity images in Lya, Halpha, and UV, and maps of Halpha/Hbeta, Lya equivalent width (EW), and Lya/Halpha. We present Lya and UV light profiles and show they are well-fitted by S\'ersic profiles, but Lya profiles show indices systematically lower than those of the UV (n approx 1-2 instead of >~4). This reveals a general lack of the central concentration in Lya that is ubiquitous in the UV. Photometric growth curves increase more slowly for Lya than the FUV, showing that small apertures may underestimate the EW. For most galaxies, however, flux and EW curves flatten by radii ~10 kpc, suggesting that if placed at high-z, only a few of our galaxies would suffer from large flux losses. We compute global properties of the sample in large apertures, and show total luminosities to be independent of all other quantities. Normalized Lya throughput, however, shows significant correlations: escape is found to be higher in galaxies of lower star formation rate, dust content, mass, and several quantities that suggest harder ionizing continuum and lower metallicity. Eight galaxies could be selected as high-z Lya emitters, based upon their luminosity and EW. We discuss the results in the context of high-z Lya and UV samples. A few galaxies have EWs above 50 AA, and one shows f_escLya of 80%; such objects have not previously been reported at low-z.