The Effect of Filaments and Tendrils on the HI Content of Galaxies
  We use the ALFALFA HI survey to examine whether the cold gas reservoirs of
galaxies are inhibited or enhanced in large-scale filaments. Our sample
includes 9947 late-type galaxies with HI detections, and 4236 late-type
galaxies with well-determined HI detection limits that we incorporate using
survival analysis statistics. We find that, even at fixed local density and
stellar mass, and with group galaxies removed, the HI deficiency of galaxies in
the stellar mass range 8.5 <log(M/Mo) < 10.5 decreases with distance from the
filament spine, suggesting that galaxies are cut off from their supply of cold
gas in this environment. We also find that, at fixed local density and stellar
mass, the galaxies that are the most gas-rich are those in small, correlated
"tendril" structures within voids: although galaxies in tendrils are in
significantly denser environments, on average, than galaxies in voids, they are
not redder or more HI deficient. This stands in contrast to the fact that
galaxies in tendrils are more massive than those in voids, suggesting a more
advanced stage of evolution. Finally, at fixed stellar mass and color, galaxies
closer to the filament spine, or in high density environments, are more
deficient in HI. This fits a picture where, as galaxies enter denser regions,
they first lose HI gas and then redden as star formation is reduced.
