The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lya Photons: A Case Study of a Protocluster field at z = 3.1

TL;DR

This study analyzes how dust, UV luminosity, and environment influence Lya photon escape in 93 galaxies at z=3.1, revealing complex ISM effects and environmental differences in Lya escape fractions.

Contribution

It provides the first detailed characterization of Lya escape properties in a protocluster environment at high redshift, highlighting the impact of environment and galaxy properties on Lya transmission.

Findings

Median Lya halo scale length is 4.9 kpc.

Total Lya escape fraction is approximately 40%.

Protocluster LAEs are bluer, more UV-luminous, and have higher escape fractions.

Abstract

We present a detailed characterization of the Lya properties for 93 Lya emitters (LAEs) at z~3.1 selected from the D1 field of the Canada-France-Hawaii-Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lya image shows an extended Lya halo (LAH) surrounding the galaxy with the exponential scale length 4.9+/-0.7kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lya escape fraction, f_esc, is 40+/-26%. Combining the dataset with existing measurements, we find a dependence of f_esc on the galaxy's UV slope (beta) and UV luminosity (L_UV). The simultaneous use of both parameters allows prediction of f_esc within 0.18dex, a substantial improvement over 0.23dex when only beta is used. The correlation between f_esc and E(B-V) suggests that Lya photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lya transmission is typically higher than that expected for continuum photons at similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lya transmission or production. Alternatively, the dust law may change with luminosity leading to over-or under-estimation of f_esc. Finally, we report that protocluster member LAEs tend to be bluer and more UV-luminous than their field cousins, resulting in systematically higher f_esc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.