Environmental quenching and galactic conformity in the galaxy cross-correlation signal

Abstract

It has long been known that environment has a large effect on star formation in galaxies. There are several known plausible mechanisms to remove the cool gas needed for star formation, such as strangulation, harassment and ram-pressure stripping.It is unclear which process is dominant, and over what range of stellar mass. In this paper, we find evidence for suppression of the cross-correlation function between massive galaxies and less massive star-forming galaxies, giving a measure of how less likely a galaxy is to be star-forming in the vicinity of a more massive galaxy. We develop a formalism for modelling environmental quenching mechanisms within the Halo Occupation Distribution scheme. We find that at $z \sim 2$ environment is not a significant factor in determining quenching of star-forming galaxies, and that galaxies are quenched with similar probabilities when they are satellites in sub-group environments, as they are globally. However, by $z \sim 0.5$ galaxies are much less likely to be star forming when in a high density (group or low-mass cluster) environment than when not. This increased probability of being quenched does not appear to have significant radial dependence within the halo at lower redshifts, supportive of the quenching being caused by the halting of fresh inflows of pristine gas, as opposed to by tidal stripping. Furthermore, by separating the massive sample into passive and star-forming, we see that this effect is further enhanced when the central galaxy is passive, a manifestation of galactic conformity.