Surface Brightness Profile of Lyman-α Halos out to 320 kpc in HETDEX

We present the median-stacked Lyman -α ( Ly α ) surface brightness profiles of 968 spectroscopically selected Ly α emitting galaxies (LAEs) at redshifts 1.9 < z < 3.5 in the early data of the Hobby-Eberly Telescope Dark Energy Experiment. The selected LAEs are high-confidence Ly α detections with high signal-to-noise ratios observed with good seeing conditions (point-spread function FWHM 80 kpc, our profile is flatter than the MUSE model. The measured profile agrees at most radii with that of galaxies in the Byrohl et al. cosmological radiative transfer simulation at z = 3. This suggests that the surface brightness of a Ly α halo at r ≲ 100 kpc is dominated by resonant scattering of Ly α photons from star-forming regions in the central galaxy, whereas at r > 100 kpc, it is dominated by photons from galaxies in surrounding dark matter halos.