xGASS group central galaxies

Results from:

Janowiecki et al. 2017, MNRAS, 466, 4795-4812 on arXiv

In the low redshift universe, observations of gas and star formation in galaxies have shown dramatic contrasts between rich clusters and the isolated field environments. Broadly speaking, galaxies in clusters are redder, more gas-poor, less star-forming, while galaxies in isolation are bluer, gas-rich, and star-forming (e.g., Dressler 1980, Kauffmann et al. 2004). While galaxies can rapidly evolve from blue to red as they join a cluster (e.g., through ram-pressure stripping and the quenching of star formation), these dramatic interactions are not enough to account for the populations of galaxies found in different environments. Given the universal galaxy scaling relations observed across all environments (Blanton & Moustakas 2009), pre-processing must play a role and we expect galaxies to be affected by their environments even outside of rich clusters.

Using the new xGASS sample of galaxies (webpage link TBD), we have compared the HI properties of galaxies sorted by environment*:

--Isolated galaxies (not members of any group)

--Central galaxies in groups (i.e. most massive in their group)

--Satellite galaxies in groups

(*Here environment comes from the SDSS group catalogs from Yang et al.)

When we compare the HI content of isolated centrals and group centrals at fixed stellar mass, an unexpected trend emerges at low masses (un-shaded are of plot below). Large points show averages in bins of stellar mass (red: isolated, green: group).