A Faint Flux-Limited Lyman Alpha Emitter Sample at $z\sim0.3$

Abstract

We present a flux-limited sample of $z\sim0.3$ Ly$α$ emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism spectroscopic data. The published GALEX $z\sim0.3$ LAE sample is pre-selected from continuum-bright objects and thus is biased against high equivalent width (EW) LAEs. We remove this continuum pre-selection and compute the EW distribution and the luminosity function of the Ly$α$ emission line directly from our sample. We examine the evolution of these quantities from $z\sim0.3$ to $2.2$ and find that the EW distribution shows little evidence for evolution over this redshift range. As shown by previous studies, the Ly$α$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$α$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$α$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$α$ escape fraction. Finally, we show that the observed Ly$α$ luminosity density from AGNs is comparable to the observed Ly$α$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$α$ luminosity density persists out to $z\sim2.2$.

27 pages, 19 figures, accepted for publication in ApJ