The impact of ram pressure on cluster galaxies, insights from GAEA and TNG

Ram pressure stripping (RPS) has a non-negligible impact on the gas content of cluster galaxies. We use the semi-analytic model GAEA and the hydro-simulation TNG to investigate whether cluster galaxies suffer a strong RPS that is sufficient to remove a significant fraction of their gas during the first pericentric passage. We estimate that a ram pressure of $10^{-10.5}$, $10^{-12} $, $10^{-13.5} $ $g cm^{-1} s^{-2}$ can remove at most $90\%$, $50\%$, and $20\%$ of the cold gas reservoir from low-mass galaxies with $9<\log M_{\star}/{\rm M}_{\odot} <9.5$, assuming the gas can be stripped instantaneously. We then use this information to divide the phase space diagram into `strong', `moderate', `weak', and `no' RPS zones. By tracing the orbit of galaxies since $2.5R_{vir}$, we find in both GAEA and TNG that about half of the galaxies in Virgo-like halos ($\log M_h / M_{\odot} \sim 14 $) did not suffer strong RPS during the first pericentric passage. In Coma-like halos ($\log M_h / M_{\odot} \sim 15$), almost all galaxies have suffered strong RPS during the first pericentric passage, which can remove all gas from low-mass galaxies but is insufficient to significantly reduce the gas content of more massive galaxies. In general, results from TNG and GAEA are consistent, with the RPS being only slightly stronger in TNG than in GAEA. Our findings suggest that most cluster galaxies will maintain a notable fraction of their gas and continue forming stars after the first pericentric passage, except for those with low stellar mass ($\log M_{\star}/{\rm M}_{\odot} <9.5$) in very massive halos ($\log M_{h}/{\rm M}_{\odot} > 15$).