Evidence for Spatially Compact Lyman Alpha Emission in z=3.1 Lyman-Alpha-Emitting Galaxies

TL;DR

This study uses high-resolution imaging to show that Lyman Alpha emission in z=3.1 galaxies is spatially compact, mostly coincident with UV sources, and not significantly more extended than the UV continuum.

Contribution

First high-resolution imaging confirms that Lyman Alpha emission in these galaxies is confined within ~2 kpc, aligning with UV emission regions, refining understanding of their spatial structure.

Findings

Lyman Alpha emission is spatially coincident with UV sources within ~0.5 kpc.

Most Lyman Alpha emission originates from regions smaller than 2 kpc.

Ground-based measurements capture over 68-78% of total Lyman Alpha flux.

Abstract

We present the results of a high-spatial-resolution study of the line emission in a sample of z=3.1 Lyman-Alpha-Emitting Galaxies (LAEs) in the Extended Chandra Deep Field-South. Of the eight objects with coverage in our HST/WFPC2 narrow-band imaging, two have clear detections and an additional two are barely detected (~2-sigma). The clear detections are within ~0.5 kpc of the centroid of the corresponding rest-UV continuum source, suggesting that the line-emitting gas and young stars in LAEs are spatially coincident. The brightest object exhibits extended emission with a half-light radius of ~1.5 kpc, but a stack of the remaining LAE surface brightness profiles is consistent with the WFPC2 point spread function. This suggests that the Lyman Alpha emission in these objects originates from a compact (<~2 kpc) region and cannot be significantly more extended than the far-UV continuum emission (<~1 kpc). Comparing our WFPC2 photometry to previous ground-based measurements of their monochromatic fluxes, we find at 95% (99.7%) confidence that we cannot be missing more than 22% (32%) of the Lyman Alpha emission.