HOW LYMAN ALPHA EMISSION DEPENDS ON GALAXY STELLAR MASS

Abstract

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 < log M * / M ⊙ < 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 * ) − 1 A ( 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.