Ly{\alpha} Emission from High Redshift Sources in COSMOS

TL;DR

This study analyzes Lyα emission and escape fractions in high-redshift galaxies from COSMOS, revealing that dust extinction significantly influences Lyα photon escape, with no evolution observed across redshifts.

Contribution

It provides the first comprehensive spectroscopic analysis of Lyα equivalent widths and escape fractions in a large sample of high-redshift galaxies from COSMOS.

Findings

Lyα equivalent width distribution shows no redshift evolution.

LAEs have higher and more variable escape fractions than LBGs.

Dust extinction is the primary factor affecting Lyα photon escape.

Abstract

We investigate spectroscopically measured Ly{\alpha} equivalent widths and escape fractions of 244 sources of which 95 are Lyman Break Galaxies (LBGs) and 106 Lyman Alpha Emitters (LAEs) at z~4.2, z~4.8, and z~5.6 selected from intermediate and narrow band observations. The sources were selected from the Cosmic Evolution Survey (COSMOS), and observed with the DEIMOS spectrograph. We find that the distribution of equivalent widths shows no evolution with redshift for both the LBG selected sources and the intermediate/narrowband LAEs. We also find that the Ly{\alpha} escape fraction of intermediate and narrow band LAEs is on average higher and has a larger variation than the escape fraction of LBG selected sources. The escape fraction does not show a dependence with redshift. Similar to what has been found for LAEs at low redshifts, the sources with the highest extinctions show the lowest escape fractions. The range of escape fractions increases with decreasing extinction. This is evidence that the dust extinction is the most important factor affecting the escape of Ly{\alpha} photons, but at low extinctions other factors such as HI covering fraction and gas kinematics can be just as effective at inhibiting the escape of Ly{\alpha} photons.