Galaxy

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.

We present an analysis of age, metal abundance, and positional data on populous clusters in the Small Magellanic Cloud (SMC) with the ultimate aim of determining the line-of-sight (LOS) depth of the SMC using these clusters as proxies. Our dataset contains 12 objects and is limited to clusters with the highest quality data for which the ages and abundances are best known and can be placed on an internally consistent scale. We have analyzed the variation of the clusters' properties with position on the sky and with line-of-sight depth. Based on this analysis, we draw the following conclusions. 1) The observational data indicates that the eastern side of the SMC (facing the LMC) contains younger and more metal-rich clusters as compared with the western side. This is not a strong correlation because our dataset of clusters is necessarily limited, but it is suggestive and warrants further study. 2) Depending on how the reddening is computed to our clusters, we find a mean distance modulus that ranges from (m − M) 0 = 18.71 ± 0.06 to (m − M) 0 = 18.82 ± 0.05. 3) The intrinsic ±1-σ line-of-sight depth of the SMC populous clusters in our study is between ∼ 6 kpc and ∼ 12 kpc depending primarily on whether we adopt the Burstein & Heiles reddenings or those from Schlegel et al. 4) Viewing the SMC as a triaxial galaxywith the Declination, Right Ascension, and LOS depth as the three axes, we find axial ratios of approximately 1:2:4. Taken together, these conclusions largely agree with those of previous investigators and serve to underscore the utility of populous star clusters as probes of the structure of the Small Magellanic Cloud.

We present a multi-wavelength study of NGC 4330, a highly-inclined spiral galaxy in the Virgo Cluster which is a clear example of strong, ongoing ICM-ISM ram pressure stripping. The HI has been removed from well within the undisturbed old stellar disk, to 50% -65% of R 25 . Multi-wavelength data (WIYN a BVR-Hα, VLA b 21-cm HI and radio continuum, and GALEX c NUV and FUV) reveal several one-sided extraplanar features likely caused by ram pressure at an intermediate disk-wind angle. At the leading edge of the interaction, the Hα and dust extinction curve sharply out of the disk in a remarkable and distinctive "upturn" feature that may be generally useful as a diagnostic indicator of active ram pressure. On the trailing side, the ISM is stretched out in a long tail which contains 10% of the galaxy's total HI emission, 6 -9% of its NUV-FUV emission, but only 2% of the Hα. The centroid of the HI tail is downwind of the UV/Hα tail, suggesting that the ICM wind has shifted most of the ISM downwind over the course of the past 10 -300 Myr. Along the major axis, the disk is highly asymmetric in the UV, but more symmetric in Hα and HI, also implying recent changes in the distributions of gas and star formation. The UV-optical colors indicate very different star formation histories for the leading and trailing sides of the galaxy. On the leading side, a strong gradient in the UV-optical colors of the gas-stripped disk suggests that it has taken 200-400 Myr to strip the gas from a radius of >8 to 5 kpc, but on the trailing side there is no age gradient. All our data suggest a scenario in which NGC 4330 is falling into cluster center for first time and has experienced a significant increase in ram pressure over the last 200-400 Myr.