Studying Inter-Cluster Galaxy Filaments Through Stacking GMBCG Galaxy
  Cluster Pairs
  We present a method to study the photometric properties of galaxies in
filaments by stacking the galaxy populations between pairs of galaxy clusters.
Using Sloan Digital Sky Survey data, this method can detect the inter-cluster
filament galaxy overdensity with a significance of $\sim 5 \sigma$ out to
$z=0.40$. Using this approach, we study the $g-r$ color and luminosity
distribution of filament galaxies as a function of redshift. Consistent with
expectation, filament galaxies are bimodal in their color distribution and
contain a larger blue galaxy population than clusters. Filament galaxies are
also generally fainter than cluster galaxies. More interestingly, the observed
filament population seems to show redshift evolution at $0.12<z<0.40$: the blue
galaxy fraction has a trend to increase at higher redshift: a filament "Butcher
Oemler Effect". We test the dependence of the observed filament density on the
richness of the cluster pair: richer clusters are connected by higher density
filaments. We also test the spatial dependence of filament galaxy overdensity:
this quantity decreases when moving away from the inter-cluster axis between a
cluster pair. This method provides an economical way to probe the photometric
properties of filament galaxies and should prove useful for upcoming projects
like the Dark Energy Survey.
