How Lyman Alpha Emission Depends on Galaxy Stellar Mass

Abstract

In this work, we show how the stellar mass (M _*) of galaxies affects the 3 < z < 4.6 Lyα equivalent width (EW) distribution. To this end, we design a sample of 629 galaxies in the M _* range 7.6\lt {log}{M}_*/{M}_⊙ \lt 10.6 from the 3D-HST/CANDELS survey. We perform spectroscopic observations of this sample using the Michigan/Magellan Fiber System, allowing us to measure Lyα fluxes and use 3D-HST/CANDELS ancillary data. In order to study the Lyα EW distribution dependence on M _*, we split the whole sample in three stellar mass bins. We find that, in all bins, the distribution is best represented by an exponential profile of the form {dN}({M}_*)/d{EW}={W}₀{({M}_*)}^-1A({M}_*){e}^-{EW/{W}₀({M}_*)}. Through a Bayesian analysis, we confirm that lower M _* galaxies have higher Lyα EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W ₀ of the distribution anti-correlate with M _*, recovering expressions of the forms A({M}_*)=-0.26(.13){log}{M}_*/{M}_⊙ +3.01(1.2) and {W}₀({M}_*)=-15.6(3.5){log}{M}_*/{M}_⊙ +166(34). These results are crucial for proper interpretation of Lyα emission trends reported in the literature that may be affected by strong M _* selection biases.