Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4

TL;DR

This study presents high-redshift imaging of Lyman alpha emission in galaxies at z=4.4, revealing extended emission regions and complex photon escape mechanisms, advancing understanding of early galaxy properties.

Contribution

It provides the first resolved Lyman alpha imaging for multiple galaxies at z=4.4, showing extended emission and challenging simple models of photon escape.

Findings

Lyman alpha emission is more extended than UV continuum in observed galaxies.

HST-detected Lyman alpha flux is less than ground-based observations, indicating diffuse halos.

No significant positional offset between Lyman alpha and UV emission regions.

Abstract

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.