Low and High Surface Brightness Galaxies at Void Walls
  We study the relative fraction of low and high surface brightness galaxies
(LSBGs and HSBGs) at void walls in the SDSS DR7. We focus on galaxies in equal
local density environments. We assume that the host dark-matter halo mass (for
which we use SDSS group masses) is a good indicator of local density. This
analysis allows to examine the behavior of the abundance of LSBG and HSBG
galaxies at a fixed local density and distinguish the large-scale environment
defined by the void geometry. We compare galaxies in the field, and in the void
walls; the latter are defined as the volume of void shells of radius equal to
that of the void. We find a significant decrement, a factor $\sim 4$, of the
relative fraction of blue, active star-forming LSBGs in equal mass groups at
the void walls and the field. This decrement is consistent with an increase of
the fraction of blue, active star-forming HSBGs. By contrast, red LSBGs and
HSBGs show negligible changes. We argue that these results are consistent with
a scenario where LSBGs with blue colors and strong star formation activity at
the void walls are fueled by gas from the expanding void regions. This process
could lead to LSBG to HSBG transformations.
