Context. The transport of Lyα photons in galaxies is a complex process and the conditions under which Lyα photons manage to escape from certain galaxies is still under investigation. The Lyman alpha reference sample (LARS) is a sample of 14 local starforming galaxies, designed to study Lyα in detail and relate it to rest-frame UV and optical emission. Aims. With the aim of identifying rest-frame UV and optical properties, which are typical of Lyα emitters (LAEs, galaxies with EW(Lyα) > 20 Å) at both low and high redshift, we investigated the morphological properties of the LARS galaxies, in particular the ones that exhibit intense Lyα radiation. Methods. We measured sizes and morphological parameters in the continuum, Lyα, and Hα images. We studied morphology by using the Gini coefficient vs. M20 and asymmetry vs. concentration diagrams. We then simulated LARS galaxies at z ∼ 2 and 5.7, performing the same morphological measurements. We also investigated the detectability of LARS galaxies in current deep field observations. The subsample of LAEs within LARS (LARS-LAEs) was stacked to provide a comparison to stacking studies performed at high redshift. Results. LARS galaxies have continuum size, stellar mass, and rest-frame absolute magnitude typical of Lyman break analogues in the local Universe and also similar to 2 < z < 3 star-forming galaxies and massive LAEs. LARS optical morphology is consistent with the one of merging systems, and irregular or starburst galaxies. For the first time we quantify the morphology in Lyα images: even if a variety of intrinsic conditions of the interstellar medium can favour the escape of Lyα photons, LARS-LAEs appear small in the continuum, and their Lyα is compact. LARS galaxies tend to be more extended in Lyα than in the rest-frame UV. It means that Lyα photons escape by forming haloes around HII regions of LARS galaxies. Conclusions. The stack of LARS-LAE Lyα images is peaked in the centre, indicating that the conditions, which make a galaxy an LAE, tend to produce a concentrated surface brightness profile. On the other hand, the stack of all LARS galaxies is shallower and more extended. This can be caused by the variety of dust and HI amount and distribution, which produces a more complex, patchy, and extended profile, like the one observed for Lyman break galaxies that can contribute to the stack. We cannot identify a single morphological property that controls whether a galaxy emits a net positive Lyα flux. However, the LARS-LAEs have continuum properties consistent with merging systems.

We present new H I imaging and spectroscopy of the 14 UV-selected starforming galaxies in the Lyman Alpha Reference Sample (LARS), aimed for a detailed study of the processes governing the production, propagation, and escape of Lyα photons. New H I spectroscopy, obtained with the 100m Green Bank Telescope (GBT), robustly detects the H I spectral line in 11 of the 14 observed LARS galaxies (although the profiles of two of the galaxies are likely confused by other sources within the GBT beam); the three highest redshift galaxies are not detected at our current sensitivity limits. The GBT profiles are used to derive fundamental H I line properties of the LARS galaxies. We also present new pilot H I spectral line imaging of 5 of the LARS galaxies obtained with the Karl G. Jansky Very Large Array (VLA). This imaging localizes the H I gas and provides a measurement of the total H I mass in each galaxy. In one system, LARS 03 (UGC 8335 or Arp 238), VLA observations reveal an enormous tidal structure that extends over 160 kpc from the main interacting systems and that contains >10 9 M of H I. We compare various H I properties with global Lyα quantities derived from HST measurements. The measurements of the Lyα escape fraction are coupled with the new direct measurements of H I mass and significantly disturbed H I velocities. Our robustly detected sample reveals that both total H I mass and linewidth are tentatively correlated with key Lyα tracers. Further, on global scales, these data support a complex coupling between Lyα propagation and the H I properties of the surrounding medium.

We present the results of H i observations of five groups of galaxies spanning a range of velocity dispersion and spiral fraction (brightest optical group member in parenthesis): NGC 7582 (NGC 7552), USGC U207 (NGC 2759), USGC U070 (NGC 664), USGC U412 (NGC 3822), USGC U451 (NGC 4065). Neutral intragroup gas is detected in three of the five groups. We present the discovery of a previously uncataloged galaxy in the USGC U070 group at α(2000) = 01 h 45 m 27 s , δ(2000) = +0436 19 , which we are designating FSW J014526.92+043619.1. We compile an H i mass function for the group environment and find that the faint-end slope is consistent with being flat.