Galactic star formation enhanced and quenched by ram pressure in groups and clusters (1311.3010v1)

Abstract: We investigate how ram pressure of intragroup and intracluster medium can influence the spatial and temporal variations of star formation (SF) of disk galaxies with halo masses (M_h) ranging from 10^10 M_sun to 10^12 M_sun (i.e., from dwarf irregular to Milky Way-type) in groups and clusters with 10^13 < M_h/M_sun < 10^15 by using numerical simulations with a new model for time-varying ram pressure. The long-term evolution of SF rates and H_alpha morphologies corresponding to the distributions of star-forming regions are particularly investigated for different model parameters. The principal results are as follows. Whether ram pressure can enhance or reduce SF depends on M_h of disk galaxies and inclination angles of gas disks with respect to their orbital directions for a given orbit and a given environment. For example, SF can be moderately enhanced in disk galaxies with M_h=10^12 M_sun at the pericenter passages in a cluster with M_h=10^14 M_sun whereas it can be completely shut down (`quenching') for low-mass disks with M_h=10^10 M_sun. Ram pressure can reduce the H_alpha-to-optical-disk-size ratios of disks and the revel of the reduction depends on M_h and orbits of disk galaxies for a given environment. Disk galaxies under strong ram pressure show characteristic H_alpha morphologies such as ring-like, one-sided, and crescent-like distributions.