How Lyman Alpha Emission Depends On Galaxy Stellar Mass

TL;DR

This study investigates how galaxy stellar mass influences the distribution of Ly-alpha equivalent widths at redshifts 3 to 4.6, revealing that lower mass galaxies tend to have higher Ly-alpha EWs and that distribution parameters depend on stellar mass.

Contribution

The paper provides a detailed analysis of the dependence of Ly-alpha EW distribution on galaxy stellar mass using a large spectroscopic sample and Bayesian methods, highlighting the importance of mass selection biases.

Findings

Lower mass galaxies have higher Ly-alpha EWs.

Distribution parameters A and W0 anti-correlate with stellar mass.

Exponential profile best fits the Ly-alpha EW distribution.

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/Msun < 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= A(M)exp(-EW/W0(M))/W0(M). Through a Bayesian analysis, we confirm that lower M galaxies have higher Ly-alpha EWs. We also find that the fraction A of galaxies featuring emission and the e-folding scale W0 of the distribution anti- correlate with M, recovering expressions of the forms A(M)= -0.26(.13) logM/Msun+3.01(1.2) and W0(M)= -15.6(3.5) logM/Msun +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.