Evolution of the Lyman-{\alpha} emitting fraction and UV properties of lensed star-forming galaxies between 2.9 < z < 6.7

TL;DR

This study analyzes the evolution of Lyman-alpha emitter fractions and UV properties of faint, lensed star-forming galaxies from redshift 2.9 to 6.7, revealing insights into reionisation and galaxy populations.

Contribution

It provides the largest sample of faint galaxies to date, examining the relationship between Lyman-alpha emission, UV brightness, and redshift, with new findings on galaxy populations in reionised bubbles.

Findings

Lyman-alpha emitter fraction decreases above z=6, indicating increasing IGM neutrality.

UV-brighter galaxies have higher Lyman-alpha fractions, especially at higher redshifts.

Fainter galaxies show trends of high star formation and low dust content, with stronger LAEs being fainter and having steeper UV slopes.

Abstract

Faint galaxies are theorised to have played a major role in reionising the Universe. Their properties as well as the Lyman-{\alpha} emitter fraction, could provide useful insight into this epoch. We use four galaxy clusters from the Lensed Lyman-alpha MUSE Arcs Sample (LLAMAS) which also have deep HST photometry to select a population of intrinsically faint Lyman Break Galaxies (LBGs) and Lyman-alpha Emitters (LAEs). We study the interrelation of these two populations, their properties, and the fraction of LBGs that display Lyman-alpha emission. The use of lensing clusters allows us to access an intrinsically faint population, the largest sample collected for this purpose: 263 LAEs and 972 LBGs between redshifts of 2.9 and 6.7, Lyman-alpha luminosities between 39.5 < log(L)(erg/s) < 42 and absolute UV magnitudes between -22 < M1500 < -12. We find a redshift evolution of the Lyman-alpha emitter fraction in line with past results, with diminished values above z = 6, taken to signify an increasingly neutral intervening IGM. Inspecting this redshift evolution with different limits on Lyman-alpha equivalent width (EW) and M1500 we find that the Lyman-alpha emitter fraction for the UV-brighter half of our sample is higher than the fraction for the UV-fainter half, a difference which increases at higher redshift. This is a surprising result and can be interpreted as a population of low Lyman-alpha EW, UV-bright galaxies situated in reionised bubbles. This result is especially interesting in the context of similar, UV-bright, low Lyman-alpha EW objects recently detected around the epoch of reionisation. We extend to intrinsically fainter objects the previously observed trends of LAEs among LBGs as galaxies with high star-formation rates and low dust content, as well as the strongest LAEs having in general fainter UV magnitudes and steeper UV slopes.