A Correlation Between Ly{\alpha} Spectral Line Profile and Rest-Frame UV Morphology

TL;DR

This study investigates the connection between Lyα spectral line shapes and UV galaxy morphology at high redshift, revealing that Lyα emission asymmetry correlates with galaxy elongation and suggests outflows rather than symmetric disks.

Contribution

It provides new observational evidence linking Lyα spectral asymmetry to galaxy morphology and supports the outflow model for high-redshift Lyα emitters.

Findings

Lyα skewness decreases with increasing axial ratio.

No evolution in Lyα asymmetry or axial ratio over cosmic time.

High-redshift Lyα emitters likely host galactic outflows.

Abstract

We explore the relationship between the spectral shape of the Ly{\alpha} emission and the UV morphology of the host galaxy using a sample of 304 Ly{\alpha}-emitting BV i-dropouts at 3 < z < 7 in the GOODS and COSMOS fields. Using our extensive reservoir of high-quality Keck DEIMOS spectra combined with HST WFC3 data, we measure the Ly{\alpha} line asymmetries for individual galaxies and compare them to axial ratios measured from observed J- and H-band (restframe UV) images. We find that the Ly{\alpha} skewness exhibits a large scatter at small elongation (a/b < 2), and this scatter decreases as axial ratio increases. Comparison of this trend to radiative transfer models and various results from literature suggests that these high-redshift Ly{\alpha} emitters are not likely to be intrinsically round and symmetric disks, but they probably host galactic outflows traced by Ly{\alpha} emitting clouds. The ionizing sources are centrally located, with the optical depth a good indicator of the absorption and scattering events on the escape path of Ly{\alpha} photons from the source. Our results find no evidence for evolution in Ly{\alpha} asymmetry or axial ratio with look-back time.