Kavli Affiliate: Eiichiro Komatsu
| First 5 Authors: Maja Lujan Niemeyer, Eiichiro Komatsu, Chris Byrohl, Dustin Davis, Maximilian Fabricius
| Summary:
We present the median-stacked Lyman-$alpha$ surface brightness profile of
968 spectroscopically selected Lyman-$alpha$ emitting galaxies (LAEs) at
redshifts $1.9<z<3.5$ in the early data of the Hobby-Eberly Telescope Dark
Energy Experiment (HETDEX). The selected LAEs are high-confidence
Lyman-$alpha$ detections with large signal-to-noise ratios observed with good
seeing conditions (point-spread-function full-width-at-half-maximum $<1.4"$),
excluding active galactic nuclei (AGN). The Lyman-$alpha$ luminosities of the
LAEs are $10^{42.4}-10^{43}, mathrm{erg}, mathrm{s}^{-1}$. We detect faint
emission in the median-stacked radial profiles at the level of $(3.6pm
1.3)times
10^{-20},mathrm{erg},mathrm{s}^{-1},mathrm{cm}^{-2},mathrm{arcsec}^{-2}$
from the surrounding Lyman-$alpha$ halos out to $rsimeq 160$ kpc (physical).
The shape of the median-stacked radial profile is consistent at
$r<80,mathrm{kpc}$ with that of much fainter LAEs at $3<z<4$ observed with
the Multi Unit Spectroscopic Explorer (MUSE), indicating that the
median-stacked Lyman-$alpha$ profiles have similar shapes at redshifts $2<z<4$
and across a factor of $10$ in Lyman-$alpha$ luminosity. While we agree with
the results from the MUSE sample at $r<80,mathrm{kpc}$, we extend the profile
over a factor of two in radius. At $r>80,mathrm{kpc}$, our profile is flatter
than the MUSE model. The measured profile agrees at most radii with that of
galaxies in the Byrohl et al. (2021) cosmological radiative transfer simulation
at $z=3$. This suggests that the surface brightness of a Lyman-$alpha$ halo at
$rlesssim 100$ kpc is dominated by resonant scattering of Lyman-$alpha$
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.
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