Abstract

Spectroscopic observations of massive z > 7 galaxies selected to have extremely large [OIII] + H beta equivalent width (EW similar to 1500 angstrom) have recently revealed large Ly alpha detection rates, in contrast to the weak emission seen in the general population. Why these systems are uniquely visible in Ly alpha at redshifts where the intergalactic medium (IGM) is likely significantly neutral is not clear. With the goal of better understanding these results, we have begun a campaign with MMT and Magellan to measure Ly alpha in galaxies with similar [OIII] + H beta EWs at z similar or equal to 2-3. At these redshifts, the IGM is highly ionized, allowing us to clearly disentangle how the Ly alpha properties depend on the [OIII] + H beta EW. Here, we present Ly alpha EWs of 49 galaxies at z = 2.2-3.7 with intense [OIII] + H beta line emission (EW = 300-3000 angstrom). Our results demonstrate that strong Ly alpha emission (EW >20 angstrom) becomes more common in galaxies with larger [OIII] + H beta EW, reflecting a combination of increasingly efficient ionizing photon production and enhanced transmission of Ly alpha. Among the galaxies with the most extreme [OIII] + H beta emission (EW similar to 1500 angstrom), we find that strong Ly alpha emission is not ubiquitous, with only 50 percent of our population showing Ly alpha EW >20 angstrom. Our data suggest that the range of Ly alpha strengths is related to the observed ellipticity, with those systems that appear edge-on or elongated having weaker Ly alpha emission. We use these results to interpret the anomalous Ly alpha properties seen in z > 7 galaxies with extreme [OIII] + H beta emission and discuss implications for the escape of ionizing radiation from these extreme line emitting galaxies.