The Lyman alpha reference sample

Abstract

We present integral field spectroscopic observations with the Potsdam Multi-Aperture Spectrophotometer of all 14 galaxies in the z ∼ 0.1 Lyman Alpha Reference Sample (LARS). We produce 2D line-of-sight velocity maps and velocity dispersion maps from the Balmer α (Hα) emission in our data cubes. These maps trace the spectral and spatial properties of the LARS galaxies' intrinsic Lyα radiation field. We show our kinematic maps that are spatially registered onto the Hubble Space Telescope Hα and Lyman α (Lyα) images. We can conjecture a causal connection between spatially resolved Hα kinematics and Lyα photometry for individual galaxies, however, no general trend can be established for the whole sample. Furthermore, we compute the intrinsic velocity dispersion σ 0 , the shearing velocity v shear , and the v shear /σ 0 ratio from our kinematic maps. In general LARS galaxies are characterised by high intrinsic velocity dispersions (54 km s −1 median) and low shearing velocities (65 km s −1 median). The v shear /σ 0 values range from 0.5 to 3.2 with an average of 1.5. It is noteworthy that five galaxies of the sample are dispersion-dominated systems with v shear /σ 0 < 1, and are thus kinematically similar to turbulent star-forming galaxies seen at high redshift. When linking our kinematical statistics to the global LARS Lyα properties, we find that dispersion-dominated systems show higher Lyα equivalent widths and higher Lyα escape fractions than systems with v shear /σ 0 > 1. Our result indicates that turbulence in actively star-forming systems is causally connected to interstellar medium conditions that favour an escape of Lyα radiation.

Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances*

“…For example, the low-metallicity, star-forming dwarf galaxy IZw18 shows Lyα absorption, despite its low metallicity and young age. Also, galaxies of the LARS sample (or: local, Hα selected galaxies) with low velocity dispersion show a reduced Lyα escape (Herenz et al 2016). A large number of scatterings in static, high column density gas can lead to an efficient suppression of Lyα photons by even small amounts of dust.…”

The Lyman alpha reference sample

“…We briefly summarize the observations, data reduction, and analysis steps relevant for the present study. A more detailed description will be given in a subsequent publication that will present an analysis of the Hα kinematics of the full sample (Herenz et al 2016).…”

The Lyα Reference Sample. VIII. Characterizing Lyα Scattering in Nearby Galaxies

“…This suggests that the region has been cleared of static neutral hydrogen, either by the winds from a preponderance of supernovae or by a bubble blown out by the region's active star formation. The resulting outflows then allow Lyα photons in the wings of the line to escape (Mas-Hesse et al 2003;Rivera-Thorsen et al 2015;Herenz et al 2016). Moreover, the concentration of ionized hydrogen in the galaxy's central region (see Figure 2) indicates that most of the medium has been ionized, and is therefore transparent to Lyα photons.…”

“…One of the best samples in which to study resolved Lyα is the Lyman Alpha Reference Sample (LARS; Hayes et al 2013Hayes et al , 2014Östlin et al 2014;Pardy et al 2014;Rivera-Thorsen et al 2015;Duval et al 2016;Herenz et al 2016). The LARS sample comprises 14 nearby ( < < z 0.02 0.2) Lyα-emitting and/or absorbing galaxies with extensive Hubble Space Telescope (HST) broadband and narrowband imaging, supplemented by observations from numerous other telescopes.…”

“…One way to understand what Lyα tells us about a galaxy is to compare it to the very well understood transition of Hα, the HI Balmer transition from n=3 to n=2 at 6563Å(e.g., Hayes et al 2007;Östlin et al 2009;Herenz et al 2016). In starforming galaxies, Balmer emission serves as a proxy for the total ionizing flux of the stars embedded in the galaxies, and is therefore one of the more direct ways (when corrected for reddening) to quantify a system's current star formation (Kennicutt 1998).…”