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

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