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

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 ($\gtrsim 2\mathrm{G}\mathrm{y}\mathrm{r}$) 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 $\mathit{\text{‘cloud-wind}}\mathit{\text{interaction’}}$. 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 $\mathit{\text{‘cloud}}\mathit{\text{crushing’}}$ problem, and the $\chi <1$ regime, which we refer to as the (relatively unexplored) $\mathit{\text{‘bubble}}\mathit{\text{drag’}}$ problem. The first pericentric passage near the cluster core can rapidly – over a crossing time $t_{\mathrm{d}\mathrm{r}\mathrm{a}\mathrm{g}}\sim R\mathrm{/}{v}_{\mathrm{r}\mathrm{e}\mathrm{l}}$ – strip the CGM in the $\mathit{\text{bubble}}\mathit{\text{drag}}$ regime. The ISM stripping criterion unlike the CGM criterion, still depends on the ram pressure ${\rho }_{\mathrm{I}\mathrm{C}\mathrm{M}}{v}_{\mathrm{r}\mathrm{e}\mathrm{l}}^2$. 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.