Effects of photon trapping on the Lyman-alpha properties of star-forming galaxies

TL;DR

This study explores how photon trapping influences the Lyman-alpha emission characteristics of high-redshift star-forming galaxies, revealing that delayed photon escape can significantly boost equivalent widths and luminosities.

Contribution

It introduces a detailed analysis of photon trapping effects on Lyman-alpha properties using radiative transfer in spherical clouds, highlighting the importance of transition phases in emission enhancement.

Findings

Lyman-alpha equivalent width can reach ~1000 angstrom during photon escape transition.

Lyman-alpha luminosity can increase by a factor of a few due to photon trapping.

Line profiles can be significantly broadened by delayed photon escape.

Abstract

Recent observations show that a large number of Lyman-alpha emitters (LAEs) at high redshift z >= 3 have unusually high Lya equivalent widths (EW > 400 angstrom). However, the origin of these high EWs is an open question. Here, we investigate the impacts of photon trapping on the Lya EW and other properties by tracking the Lya radiative transfer in spherical galactic clouds. We find that the delayed escape of the Lya photons can change the Lya properties significantly. During the transition phase from optically thick to optically thin where the Lya photons can escape simultaneously, the EW can be boosted to ~ 1000 angstrom, the Lya luminosity can be increased by a factor of a few, and the line profile can be significantly broadened. The boost factor appears to depend on the galaxy properties such as mass and star formation rate and timescale, therefore future investigation combing 3D Lya RT calculations with cosmological simulations of galaxy formation and evolution is needed to fully understand the Lya properties of early star-forming galaxies.