HST emission line galaxies at z similar to 2: comparing physical properties oflyman alpha and optical emission line selected galaxies

Abstract

We compare the physical and morphological properties of z similar to 2 Ly alpha emitting galaxies (LAEs) identified in the HETDEX Pilot Survey and narrow band studies with those of z similar to 2 optical emission line selected galaxies (oELGs) identified via HST WFC3 infrared grism spectroscopy. Both sets of galaxies extend over the same range in stellar mass (7.5 < log M/M-circle dot < 10.5), size (0.5 < R < 3.0 kpc), and star formation rate (similar to 1 < SFR < 100 M-circle dot yr(-1)). Remarkably, a comparison of the most commonly used physical and morphological parameters-stellar mass, half-light radius, UV slope, SFR, ellipticity, nearest neighbor distance, star formation surface density, specific SFR, [O III] luminosity, and [O III] equivalent width-reveals no statistically significant differences between the populations. This suggests that the processes and conditions which regulate the escape of Ly alpha from a z similar to 2 star-forming galaxy do not depend on these quantities. In particular, the lack of dependence on the UV slope suggests that Ly alpha emission is not being significantly modulated by diffuse dust in the interstellar medium. We develop a simple model of Ly alpha emission that connects LAEs to all high-redshift starforming galaxies where the escape of Ly alpha depends on the sightline through the galaxy. Using this model, we find that mean solid angle for Ly alpha escape is Omega(Ly alpha) = 2.4 +/- 0.8 steradians; this value is consistent with those calculated from other studies.