The Utility of Lyman-alpha Emission Lines as a Probe of Interactions between High Redshift Galaxies and their Environments

TL;DR

This study examines how instrumental effects influence measurements of Lyman-alpha emission line asymmetry in high redshift galaxies, proposing corrections and assessing the reliability of different asymmetry parameters for probing galaxy-environment interactions.

Contribution

The paper models instrumental effects on Lyman-alpha skewness measurements and recommends more robust parameters like B/R for analyzing high redshift galaxy spectra.

Findings

Significant uncertainty in skewness at low resolution (R<3000).

Masking sky lines introduces substantial errors.

No strong correlation between skewness and galaxy properties.

Abstract

The Lyman-alpha emission line is the strongest feature in the spectrum of most high redshift galaxies, and is typically observed as being highly asymmetric due to galactic outflows. Quantifying this asymmetry is challenging. Here, we explore how measurements of one parameterisation, Lyman-alpha skewness, are affected by instrumental resolution and detection signal-to-noise and thus whether this can be extended throughout the archive. We model these effects through simulated lines and apply our derived corrections to existing archival data sets (including sources observed with FORS2 and DEIMOS) to reconstruct the intrinsic line emission parameters. We find a large uncertainty in parameter reconstruction at low resolutions (R<3000) and high skew values, as well as substantial random errors resulting from the masking of sky lines. We suggest that interpretations of spectral line asymmetry should be made with caution, while a simpler parametrization, like B/R (blue-red flux asymmetry), is likely to yield more robust results. We see a possible weak trend in velocity width with mass, although there is no evidence in the data for a reliable correlation of skew with galaxy mass, star formation rate or age at z=4-5. Using our results, we investigate the possibilities of recovering emission line asymmetry with current and future instruments.