We find that stripping of cold gas is ubiquitous in satellite galaxies in both group and cluster environments. In this work, we review the current status of environmental studies of cold gas in star-forming satellites in the local Universe from an observational perspective, focusing on the evidence for a physical link between cold gas stripping and quenching of the star formation. In nearby clusters, we see examples of cold gas being removed from the star-forming discs of galaxies moving through the intracluster medium, but whether active stripping is widespread and/or necessary to halt star formation in satellites, or quenching is just a consequence of the inability of these galaxies to replenish their cold gas reservoirs, remains unclear. At least for satellite galaxies, it is generally accepted that internal processes alone cannot be responsible for fully quenching their star formation, but that environment should play an important, if not dominant, role. While it is clear that the cold gas reservoir, which fuels the formation of new stars, must be affected first, how this happens and what are the dominant physical mechanisms involved is still a matter of debate. One of the key open questions in extragalactic astronomy is what stops star formation in galaxies. approximately a sound crossing time), as discussed in the text. The green dashed curve corresponds to equation (7) with α= 2 but with a time-delay factor that accounts for how long it takes for the galaxy to respond to ram pressure stripping (i.e. In both the top and bottom panels, the horizontal dotted lines correspond to the predictions of equation (7) for α= 2, 4, 6, 8 and 10 (bottom to top panel). Thus, the ram pressure is the same for both cases in the bottom panel. In the bottom panel, the same galaxy is run through two different media: the thick red curve corresponds to the case where the background density is the same as in the top panel, but the velocity is 760 km s−1, while the thin red curve corresponds to the case where the velocity is 1000 km s−1 but the density is a factor of (1000/760)2 times lower than in the top panel. The solid red and dashed blue curves show the bound mass of gas and dark matter, respectively, in the simulation. In the top panel, a galaxy of mass M200= 4 × 1012 M⊙ is run through a uniform gaseous medium of density 100 fbρcrit at a velocity of 1000 km s−1. One immediate consequence is that the colours and morphologies of satellite galaxies in groups and clusters will differ significantly from those predicted with the standard assumption of complete stripping of the hot coronae.Īn example of ram pressure stripping in the uniform medium simulations. The proposed model has several interesting applications, including modelling the ram pressure stripping of both observed and cosmologically simulated galaxies and as a way to improve present semi-analytic models of galaxy formation. The one exception involves unlikely systems where the orbit of the galaxy is highly non-radial and its mass exceeds about 10 per cent of the group or cluster into which it is falling (in which case the model underpredicts the stripping following pericentric passage). The model reproduces the results of the simulations to within ≈10 per cent at almost all times for all the orbits, mass ratios, and galaxy structural properties we have explored. The model is analogous to the original formulation of Gunn & Gott, except that it is appropriate for the case of a spherical (hot) gas distribution (as opposed to a face-on cold disc) and takes into account that stripping is not instantaneous but occurs on a characteristic time-scale. We propose a physically simple analytic model that describes the stripping seen in the simulations remarkably well. For typical structural and orbital parameters, we find that ∼30 per cent of the initial hot galactic halo gas can remain in place after 10 Gyr. The sensitivity of the results to the orbit, total galaxy mass, and galaxy structural properties is explored. We use a large suite of carefully controlled full hydrodynamic simulations to study the ram pressure stripping of the hot gaseous haloes of galaxies as they fall into massive groups and clusters.
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