The Redshift Evolution of Extended Lyα Emission in HETDEX. I. Imaging Methods and Emission Measurements

Abstract

We investigate extended Lyα emission using integral-field-unit data from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). We apply the modified Shepard method to image 106,853 Lyα emitters and median-stack them as functions of rest-frame Lyα equivalent width, Lyα line flux, and redshift to obtain accurate flux measurements for the faintest detections. After careful consideration of point-spread-function, centroiding, integral-field-unit correlation, and signal-to-noise errors, we calculate one-dimensional exponential scale lengths ranging from approximately 3.0 to 7.1 kpc. The scale lengths show a slight negative correlation with Lyα equivalent width, with lower-equivalent-width sources having larger scale lengths. We also detect positive correlations between scale length and Lyα flux and luminosity within flux- and luminosity-binned subsamples. Overall, we find evidence for a decrease in Lyα halo size with increasing redshift and discuss the mechanisms that could power these halos and drive their complex evolution.