学术文献库

Spectroscopic observations of massive $z>7$ galaxies selected to have extremely large [OIII]+H$β$ equivalent width (EW $\sim1500$ Å) have recently revealed large Ly$α$ detection rates, in contrast to the weak emission seen in the general population. Why these systems are uniquely visible in Ly$α$ at redshifts where the 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$α$ in galaxies with similar [OIII]+H$β$ EWs at $z\simeq2-3$. At these redshifts, the IGM is highly ionized, allowing us to clearly disentangle how the Ly$α$ properties depend on the [OIII]+H$β$ EW. Here we present Ly$α$ EWs of $49$ galaxies at $z=2.2-3.7$ with intense [OIII]+H$β$ line emission (EW $=300-3000$ Å). Our results demonstrate that strong Ly$α$ emission (EW $>20$ Å) becomes more common in galaxies with larger [OIII]+H$β$ EW, reflecting a combination of increasingly efficient ionizing photon production and enhanced transmission of Ly$α$. Among the galaxies with the most extreme [OIII]+H$β$ emission (EW $\sim1500$ Å), we find that strong Ly$α$ emission is not ubiquitous, with only $50$ per cent of our population showing Ly$α$ EW $>20$ Å. Our data suggest that the range of Ly$α$ strengths is related to the observed ellipticity, with those systems that appear edge-on or elongated having weaker Ly$α$ emission. We use these results to interpret the anomalous Ly$α$ properties seen in $z>7$ galaxies with extreme [OIII]+H$β$ emission and discuss implications for the escape of ionizing radiation from these extreme line emitting galaxies.