Oral Presentation

Why are the galaxies in clusters gas poor? Lessons from simulations

Author(s): Sukyoung Yi (Yonsei) S. Lyla Jung (Yonsei)

Presenter: Sukyoung Yi (Yonsei University)

Using the cosmological hydrodynamic simulations on 16 clusters, we investigate the mechanisms of gas depletion of galaxies found inside clusters. The YZiCS simulation employs the same input physics and numerical techniques as used in the Horizon-AGN simulation. The result is as follows. The gas depletion mechanisms can be categorized into three channels based on where and when they took place. First, 34% of our galaxies are gas poor before entering clusters (``pre-processing''). They are mainly satellites that have undergone the environmental effect inside group halos. Second, 43% of the sample became quickly gas deficient in clusters before the first pericentric pass (``fast cluster processing''). Some of them were group satellites that are low in gas at the time of cluster entry compared to the galaxies directly coming from the field. Even the galaxies with large gas fractions take this channel if they fall into massive clusters (>10^{14.5} Msun) or approach cluster centres through radial orbits. Third, 24% of our sample retain gas even after their first pericentric pass (``slow cluster processing'') as they fall into the less massive clusters and/or have circular orbits. The relative importance of each channel varies with a cluster's mass, while the exact degree of significance is subject to large uncertainties. Group pre-processing accounts for a third of the total gas depletion; but it also determines the gas fraction of galaxies at their cluster entry which in turn determines whether a galaxy should take the fast or the slow cluster processing.  Cluster processing appears to be more important than preprocessing, but it is the magnitude of preprocessing that determines the magnitude of cluster processing.