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 Ly alpha equivalent width (EW) distribution. To this end, we design a sample of 629 galaxies in the M-* range 7.6 < logM(*)/M-circle dot < 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 Ly alpha fluxes and use 3D-HST/CANDELS ancillary data. In order to study the Ly alpha 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-*)/dEW = W-0(M-*)(-1)A(M-*)e(-EW/W0(M*)). Through a Bayesian analysis, we confirm that lower M-* galaxies have higher Lya 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)logM(*)/M-circle dot + 3.01(1.2) and W-0(M-*) = -15.6(3.5)logM(*)/M-circle dot + 166(34). These results are crucial for proper interpretation of Ly alpha emission trends reported in the literature that may be affected by strong M-* selection biases.