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Paper: VIVA (VLA Imaging of Virgo in Atomic gas): HI Stripping in Virgo Galaxies
Volume: 395, Frontiers of Astrophysics: A Celebration of NRAO's 50th Anniversary
Page: 364
Authors: Chung, A.; van Gorkom, J.H.; Crowl, H.; Kenney, J.D.P.; Vollmer, B.
Abstract: We present results of a new Very Large Array survey of 53 Virgo galaxies (48 spirals and 5 dwarf/irregular systems). The goal is to study how the Hi gas properties are affected by the cluster environment. The survey covers galaxies in a wide range of densities from the center of the cluster to more than 3 Mpc from M87. The gas is imaged down to a column-density sensitivity of a few times 1019cm−2. We find examples of gas stripping at all stages. Within ∼0.5 Mpc from M87, most galaxies are severely HI stripped. The HI disks are truncated to well within the optical disks. While the HI looks asymmetric, the outer stellar disks look undisturbed. The fact that only the gas and not the stars has been stripped suggests that those galaxies have been affected by the hot and dense cluster gas. Interestingly we also find a few truncated disks at large projected distances from the center. Although some of these may have been stripped while crossing the cluster core, a detailed population-synthesis study of the outer disk of one of these shows that star formation was terminated recently. The time since stripping is too short for the galaxy to have traveled from the core to its current location. So at least one galaxy has lost its gas from the outer disk by another mechanism than ram-pressure stripping in the dense cluster core.

At intermediate- to low-density regions (>0.6 Mpc) we find HI tails with various lengths. We find seven galaxies with long one-sided HI tails pointing away from M87. The galaxies are at 0.6−1 Mpc from M87. Since these galaxies are only mildly HI deficient and the tails point away from M87, these galaxies are probably falling into the cluster for the first time on highly radial orbits. For all but two of the galaxies the estimated ram pressure at their location in the cluster would be sufficient to pull out the HI in the very outer disks. One galaxy also looks optically disturbed and a simulation suggests that a combination of ram pressure plus a tidal interaction has pulled out the tail.

In the outskirts of the cluster we find several examples of tidally interacting galaxies. We possibly see evidence for some accretion of gas as well. Lastly, the merging of subclusters with Virgo can cause bulk motions of the ICM. We see one example of a galaxy far out that appears to be ram-pressure stripped by a dynamic ICM.

In summary, our results show that galaxies are already affected in the low-density outer regions of the cluster through ram-pressure stripping and tidal interactions, or a combination of both.

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