A Comprehensive Study of Lyα Emission in the High-redshift Galaxy Population

Abstract

We present an exhaustive census of Lyman alpha (Lyα) emission in the general galaxy population at 3< z< 4.6. We use the Michigan/Magellan Fiber System (M2FS) spectrograph to study a stellar mass (M {}_* ) selected sample of 625 galaxies homogeneously distributed in the range 7.6< {log} {M}_* /{M}_⊙ < 10.6. Our sample is selected from the 3D-HST/CANDELS survey, which provides the complementary data to estimate Lyα equivalent widths ({W}_{Lyα }) and escape fractions (f _esc) for our galaxies. We find both quantities to anti-correlate with M _*, star formation rate (SFR), UV luminosity, and UV slope (β). We then model the {W}_{Lyα } distribution as a function of M _UV and β using a Bayesian approach. Based on our model and matching the properties of typical Lyman break galaxy (LBG) selections, we conclude that the {W}_{Lyα } distribution in such samples is heavily dependent on the limiting M _UV of the survey. Regarding narrowband surveys, we find their {W}_{Lyα } selections to bias samples toward low M _*, while their line-flux limitations preferentially leave out low-SFR galaxies. We can also use our model to predict the fraction of Lyα-emitting LBGs at 4 ≤ z ≤ 7. We show that reported drops in the Lyα fraction at z ≥ 6, usually attributed to the rapidly increasing neutral gas fraction of the universe, can also be explained by survey M _UV incompleteness. This result does not dismiss reionization occurring at z ∼ 7, but highlights that current data is not inconsistent with this process taking place at z > 7.