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

TL;DR

This study presents a flux-limited sample of Lyα emitters at z~0.3, analyzes their properties, and compares their evolution with higher redshift data, revealing minimal evolution in equivalent width distribution and significant AGN contribution.

Contribution

It provides the first unbiased measurement of Lyα emitter properties at z~0.3, removing previous selection biases and comparing evolution across redshifts.

Findings

EW distribution shows little evolution from z~0.3 to 2.2.

Lyα luminosity density decline mirrors Hα decline, indicating stable escape fraction.

AGN contribution to Lyα luminosity density remains significant up to z~2.2.

Abstract

We present a flux-limited sample of $z\sim0.3$ Ly$\alpha$ 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$\alpha$ 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$\alpha$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$\alpha$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$\alpha$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$\alpha$ escape fraction. Finally, we show that the observed Ly$\alpha$ luminosity density from AGNs is comparable to the observed Ly$\alpha$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$\alpha$ luminosity density persists out to $z\sim2.2$.