Profiles of Lyman\alpha\ Emission Lines

TL;DR

This study analyzes the Lyα emission line profiles of 91 high-redshift galaxies, revealing characteristic double-peaked profiles shaped by scattering in expanding neutral hydrogen shells, indicating burst-like star formation and gas outflows.

Contribution

First detailed analysis of Lyα line profiles at z=3.1 showing characteristic features explained by scattering in expanding hydrogen shells.

Findings

Approximately 50% show double-peaked Lyα profiles.

Red peaks are stronger and asymmetric, correlated with peak separation.

Profiles suggest starburst-driven gas outflows and scattering effects.

Abstract

We present the results of the observations of the Ly\alpha\ line profiles of 91 emission-line galaxies at z=3.1 with the spectral resolution of \lambda/\delta\lambda (FWHM) = 1700, or 180 km/s. A significant fraction, ~50% of the observed objects show the characteristic double peaks in their Ly\alpha profile. The red peak is much stronger than the blue one for most of the cases. The red peaks themselves also show weak but significant asymmetry and their widths are correlated with the velocity separation of the red and the blue peaks, which implies that the peaks are not isolated multiple components with different velocities but the parts of the single line which is modified by the absorption and/or scattering by the associated neutral hydrogen gas. The characteristic profile can be naturally explained by the scattering in the expanding shell of neutral hydrogen surrounding the Ly\alpha\ emitting region while the attenuation by the inter-galactic medium should also be considered. Our results suggest that the star-formation in these Ly\alpha\ emitters are dominated by the young burst-like events which produce the intrinsic Ly\alpha\ emission as well as the gas outflow.