The Evolution of Lyman Alpha Emitter Line Widths from z=5.7 to z=6.6

TL;DR

This study investigates how the widths of Ly-alpha emission lines in high-redshift galaxies evolve from z=5.7 to z=6.6, revealing that lower-luminosity LAEs show line narrowing while ultraluminous LAEs do not, implying differences in their ionization environments.

Contribution

It provides new observational evidence on the redshift evolution of Ly-alpha line widths across different luminosities, highlighting the distinct behaviors of ultraluminous versus lower-luminosity LAEs.

Findings

Lower-luminosity LAEs show significant line narrowing at z=6.6 compared to z=5.7.

Ultraluminous LAEs do not exhibit this narrowing, indicating different ionization conditions.

Higher redshift increases Ly-alpha scattering, but ultraluminous LAEs may be in more ionized regions.

Abstract

Recent evidence suggests that high-redshift Ly-alpha emitting galaxies (LAEs) with logL(Ly-alpha) > 43.5 erg/s, referred to as ultraluminous LAEs (ULLAEs), may show less evolution than lower-luminosity LAEs in the redshift range z=5.7-6.6. Here we explore the redshift evolution of the velocity widths of the Ly-alpha emission lines in LAEs over this redshift interval. We use new wide-field, narrowband observations from Subaru/Hyper Suprime-Cam to provide a sample of 24 z=6.6 and 12 z=5.7 LAEs with log L(Ly-alpha) > 43 erg/s, all of which have follow-up spectroscopy from Keck/DEIMOS. Combining with archival lower-luminosity data, we find a significant narrowing of the Ly-alpha lines in LAEs at logL(Ly-alpha) < 43.25 erg/s -- somewhat lower than the usual ULLAE definition -- at z = 6.6 relative to those at z = 5.7, but we do not see this in higher-luminosity LAEs. As we move to higher redshifts, the increasing neutrality of the intergalactic medium should increase the scattering of the Ly-alpha lines, making them narrower. The absence of this effect in the higher-luminosity LAEs suggests they may lie in more highly ionized regions, self-shielding from the scattering effects of the intergalactic medium.