WALLABY Pre-Pilot Survey: The effects of tidal interaction on radial
  distribution of color in galaxies of the Eridanus supergroup
  We study the tidal interaction of galaxies in the Eridanus supergroup, using
HI data from the pre-pilot survey of WALLABY (Widefield ASKAP L-band Legacy
All-sky Blind surveY). We obtain optical photometric measurements and quantify
the strength of tidal perturbation using a tidal parameter $S_{sum}$. For
low-mass galaxies of $M_* \lesssim 10^9 M_\odot$, we find a dependence of
decreasing HI-to-optical disk size ratio with increasing $S_{sum}$, but no
dependence of HI spectral line asymmetry with $S_{sum}$. This is consistent
with the behavior expected under tidal stripping. We confirm that the color
profile shape and color gradient depend on the stellar mass, but there is
additional correlation of low-mass galaxies having their color gradients within
$2R_{50}$ increasing with higher $S_{sum}$. For these low-mass galaxies, the
dependence of color gradients on $S_{sum}$ is driven by color becoming
progressively redder in the inner disk when tidal perturbations are stronger.
For high-mass galaxies, there is no dependence of color gradients on $S_{sum}$,
and we find a marginal reddening throughout the disks with increasing
$S_{sum}$. Our result highlights tidal interaction as an important
environmental effect in producing the faint end of the star formation
suppressed sequence in galaxy groups.
