Ram pressure stripping in clusters: Gravity can bind the ISM but not the CGM

Abstract

We explore the survival of a galaxy's circumgalactic medium (CGM) as it experiences ram pressure stripping (RPS) moving through the intracluster medium (ICM). For a satellite galaxy, the CGM is often assumed to be entirely stripped/evaporated, an assumption that may not always be justified. We carry out 3D-hydrodynamic simulations of the interstellar and circumgalactic media (ISM+CGM) of a galaxy like JO201 moving through the ICM. The CGM can survive long at cluster outskirts ($\gtrsim2 \rm \ Gyr$) but at smaller cluster-centric distances, 90\% of the CGM mass is lost within $\sim 500$ Myr. The gravitational restoring force on the CGM is mostly negligible and the CGM-ICM interaction is analogous to \textit{`cloud-wind interaction'}. The CGM stripping timescale does not depend on the ram pressure but on the CGM to ICM density contrast $\chi$. Two distinct regimes emerge for CGM stripping: the $\chi >1$ regime, which is the well-known \textit{`cloud crushing'} problem, and the $\chi <1$ regime, which we refer to as the (relatively unexplored) \textit{`bubble drag'} problem. The first pericentric passage near the cluster core can rapidly -- over a crossing time $t_{\rm drag} \sim R/v_{\rm rel}$ -- strip the CGM in the \textit{bubble drag} regime. The ISM stripping criterion unlike the CGM criterion, still depends on the ram pressure $\rho_{\rm ICM} v_{\rm rel}^2$. The stripped tails of satellites contain contributions from both the disk and the CGM. The X-ray plume in M89 in the Virgo cluster and a lack of it in the nearby M90 might be attributed to their orbital histories. M90 has likely undergone stripping in the bubble drag regime due to a pericentric passage close to the cluster center.