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

We present an exhaustive census of Lyman alpha (Ly alpha) 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 < logM(*)/M-circle dot < 10.6. Our sample is selected from the 3D-HST/CANDELS survey, which provides the complementary data to estimate Ly alpha equivalent widths (W-Ly alpha) 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 (beta). We then model the WLya distribution as a function of M-UV and beta using a Bayesian approach. Based on our model and matching the properties of typical Lyman break galaxy (LBG) selections, we conclude that theW(Ly alpha) distribution in such samples is heavily dependent on the limiting M-UV of the survey. Regarding narrowband surveys, we find their W-Ly alpha 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 Ly alpha-emitting LBGs at 4 <= z <= 7. We show that reported drops in the Lya 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 similar to 7, but highlights that current data is not inconsistent with this process taking place at z > 7.