Galaxy

In a new H i imaging survey of Virgo galaxies (VIVA: VLA Imaging of Virgo galaxies in Atomic gas), we find seven spiral galaxies with long H i tails. The morphology varies, but all the tails are extended well beyond the optical radii on one side. These galaxies are found in intermediate-to low-density regions (0.6-1 Mpc in projection from M87). The tails are all pointing roughly away from M87, suggesting that these tails may have been created by a global cluster mechanism. While the tidal effects of the cluster potential are too small, a rough estimate suggests that simple ram pressure stripping could have indeed formed the tails in all but two cases. At least three systems show H i truncation to within the stellar disk, providing evidence of a gas-gas interaction. Although most of these galaxies do not appear disturbed optically, some have close neighbors, suggesting that tidal interactions may have moved gas outward, making it more susceptible to the intracluster medium ram pressure or viscosity. Indeed, a simulation study of one of the tail galaxies, NGC 4654, suggests that the galaxy is most likely affected by the combined effect of a gravitational interaction and ram pressure stripping. We conclude that these one-sided H i tail galaxies have recently arrived in the cluster, falling in on highly radial orbits. It appears that galaxies begin to lose their gas already at intermediate distances from the cluster center through ram pressure or turbulent viscous stripping and tidal interactions with their neighbors, or a combination of both.

We present the results of a new VLA H i Imaging survey of Virgo galaxies, the VLA Imaging survey of Virgo galaxies in Atomic gas (VIVA). The survey includes high-resolution H i data of 53 carefully selected late type galaxies (48 spirals and five irregular systems). The goal is to study environmental effects on H i gas properties of cluster galaxies to understand which physical mechanisms affect galaxy evolution in different density regions, and to establish how far out the impact of the cluster reaches. As a dynamically young cluster, Virgo contains examples of galaxies experiencing a variety of environmental effects. Its nearness allows us to study each galaxy in great detail. We have selected Virgo galaxies with a range of star formation properties in low to high density regions (at projected distances from M87, d 87 = 0.3-3.3 Mpc). Contrary to previous studies, more than half of the galaxies in the sample (∼60%) are fainter than 12 mag in B T . Overall, the selected galaxies represent the late type Virgo galaxies (S0/a to Sd/Irr) down to m p 14.6 fairly well in morphological type, systemic velocity, subcluster membership, H i mass, and deficiency. The H i observations were done in C short (CS) configuration of the VLA radio telescope, with a typical spatial resolution of 15 and a column density sensitivity of ≈ 3-5 × 10 19 cm −2 in 3σ per 10 km s −1 channel. The survey was supplemented with data of comparable quality from the NRAO archive, taken in CS or C configuration. In this paper, we present H i channel maps, total intensity maps, velocity fields, velocity dispersions, global/radial profiles, position-velocity diagrams and overlays of H i/1.4 GHz continuum maps on the optical images. We also present H i properties such as total flux (S H i ), H i mass (M H i ), linewidths (W 20 and W 50 ), velocity (V H i ), deficiency (def H i ), and size (D eff H i and D iso H i ), and describe the H i morphology and kinematics of individual galaxies in detail. The survey has revealed details of H i features that were never seen before. In this paper, we briefly discuss differences in typical H i morphology for galaxies in regions of different galaxy densities. We confirm that galaxies near the cluster core (d 87 0.5 Mpc) have H i disks that are smaller compared to their stellar disks (D H i /D 25 < 0.5). Most of these galaxies in the core also show gas displaced from the disk, which is either currently being stripped or falling back after a stripping event. At intermediate distances (d 87 ∼ 1 Mpc) from the center, we find a remarkable number of galaxies with long one-sided H i tails pointing away from M87. In a previous letter, we argue that these galaxies are recent arrivals, falling into the Virgo core for the first time. In the outskirts, we find many gas-rich galaxies, with gas disks extending far beyond their optical disks. Interestingly, we also find some galaxies with H i disks that are smaller compared to their stellar disks at large clustercentric distances.

Long-slit stellar kinematic observations were obtained along the major axis of 30 edge-on spiral galaxies, 24 with a boxy or peanut-shaped (B/PS) bulge and six with other bulge types for comparison. Such B/ PS bulges are identified in at least 45% of highly inclined systems, and a growing body of theoretical and observational work suggests that they are the edge-on projection of thickened bars. Profiles of the mean stellar velocity V, the velocity dispersion , as well as the asymmetric (h 3 ) and symmetric (h 4 ) deviations from a pure Gaussian are presented for all objects. Comparing these profiles with stellar kinematic bar diagnostics developed from N-body simulations, we find bar signatures in 24 of our sample galaxies (80%). Galaxies with a B/ PS bulge typically show a double-humped rotation curve with an intermediate dip or plateau. They also frequently show a rather flat central velocity dispersion profile accompanied by a secondary peak or plateau, and numerous galaxies have a local central minimum (k40%). The h 3 profiles display up to three slope reversals. Most importantly, h 3 is normally correlated with V over the presumed bar length, contrary to expectations from axisymmetric disks. These characteristic bar signatures strengthen the case for a close relationship between B/ PS bulges and bars and leave little room for other explanations of the bulges' shape. We also find that h 3 is anticorrelated with V in the very center of most galaxies (k60%), indicating that these objects additionally harbor cold and dense decoupled (quasi-) axisymmetric central stellar disks, which may be related to the central light peaks. These central disks coincide with previously identified star-forming ionized-gas disks (nuclear spirals) in gas-rich systems, and we argue that they formed out of gas accumulated by the bar at its center through inflow. As suggested by N-body models, the asymmetry of the velocity profile (h 3 ) appears to be a reliable tracer of asymmetries in disks, allowing us to discriminate between axisymmetric and barred disks seen in projection. B/ PS bulges (and thus a large fraction of all bulges) appear to be made up mostly of disk material, which has acquired a large vertical extent through bar-driven vertical instabilities. Their formation is thus probably dominated by secular evolution processes rather than merging.