KK246, a dwarf galaxy with extended H I disk in the Local Void

We have found that KK 246, the only confirmed galaxy located within the nearby Tully Void, is a dwarf galaxy with an extremely extended H I disk and signs of an H I cloud with anomalous velocity. It also exhibits clear misalignment between the kinematical major and minor axes, indicative of an oval distortion, and a general misalignment between the H I and optical major axes. We measure a H I mass of 1.05 +- 0.08 x 10^8 M_sun, and a H I extent 5 times that of the stellar disk, one of the most extended H I disks known. We estimate a dynamical mass of 4.1 x 10^9 M_sun, making this also one of the darkest galaxies known, with a mass-to-light ratio of 89. The relative isolation and extreme underdense environment make this an interesting case for examining the role of gas accretion in galaxy evolution.Comment: 15 pages, 8 figures, 2 tables, accepted for publication in A

Gipsy 3D: Analysis, Visualization and Vo-Tools

The scientific goals of the AMIGA project are based on the analysis of a significant amount of spectroscopic 3D data. In order to perform this work we present an initiative to develop a new VO compliant package, including present core applications and tasks offered by the Groningen Image Processing System (GIPSY), and new ones based on use cases elaborated in collaboration with ad- vanced users. One of the main goals is to provide local interoperability between GIPSY (visualization and data analysis) and other VO software. The connectivity with the Virtual Observatory environment will provide general access to 3D data VO archives and services, maximizing the potential for scientific discovery.Comment: 2 pages, 1 figure, to appear in the proceedings of the "Multi-wavelength Astronomy and Virtual Observatory" Workshop held at ESAC 1-3 Dec 200

From gas to galaxies

The unsurpassed sensitivity and resolution of the Square Kilometer Array (SKA) will make it possible for the first time to probe the continuum emission of normal star forming galaxies out to the edges of the universe. This opens the possibility for routinely using the radio continuum emission from galaxies for cosmological research as it offers an independent probe of the evolution of the star formation density in the universe. In addition it offers the possibility to detect the first star forming objects and massive black holes. In deep surveys SKA will be able to detect HI in emission out to redshifts of $z \approx 2.5$ and hence be able to trace the conversion of gas into stars over an era where considerable evolution is taking place. Such surveys will be able to uniquely determine the respective importance of merging and accreting gas flows for galaxy formation over this redshift range (i.e. out to when the universe was only one third its present age). It is obvious that only SKA will able to see literally where and how gas is turned into stars. These and other aspects of SKA imaging of galaxies will be discussed.Comment: To be published in New Astronomy Reviews, Elsevier, Amsterdam as part of "Science with the Square Kilometre Array", eds. C. Carilli and S. Rawlings. 18 pages + 13 figures; high resolution version and other chapters of "Science with the Square Kilometre Array" available at http://www.skatelescope.org/pages/science_gen.ht

Tidal Remnants and Intergalactic HII Regions

We report the discovery of two small intergalactic HII regions in the loose group of galaxies around the field elliptical NGC 1490. The HII regions are located at least 100 kpc from any optical galaxy but are associated with a number of large HI clouds that are lying along an arc 500 kpc in length and that have no optical counterpart on the Digital Sky Survey. The sum of the HI masses of the clouds is almost 10^10 M_sun and the largest HI cloud is about 100 kpc in size. Deep optical imaging reveals a very low surface brightness counterpart to this largest HI cloud, making this one of the HI richest optical galaxies known (M_HI/L_V~200). Spectroscopy of the HII regions indicates that the abundance in these HII regions is only slightly sub-solar, excluding a primordial origin of the HI clouds. The HI clouds are perhaps remnants resulting from the tidal disruption of a reasonably sized galaxy, probably quite some time ago, by the loose group to which NGC1490 belongs. Alternatively, they are remnants of the merger that created the field elliptical NGC1490. The isolated HII regions show that star formation on a very small scale can occur in intergalactic space in gas drawn from galaxies by tidal interactions. Many such intergalactic small star formation regions may exist near tidally interacting galaxies.Comment: To appear in the proceedings of the IAU Symposium #217, Recycling Intergalactic and Interstellar Matter, eds. P.-A. Duc, J. Braine, and E. Brinks, 6 pages with low resolution figures. The full paper with high resolution images can be downloaded from http://www.astron.nl/~morganti/Papers/cloud.ps.g

ESO 381-47, an early-type galaxy with extended HI and a star forming ring

ESO 381-47 is an early type galaxy with an extended HI disk. GALEX and very deep optical images reveal a distinct stellar ring far outside the optical body with a diameter of ~30 kpc, which has undergone recent star formation at 1.8 x 10^-4 Msun/yr/kpc^-2, consistent with other new results which detect low level star formation below the traditional Kennicutt relation in the outer parts of spiral galaxies. The morphology of this galaxy resembles the recently identified class of ultraviolet objects called extended ultraviolet disks, or XUV-disks. New HI observations of this galaxy taken at the ATCA and in the CnB array at the VLA show that the cold gas lies in an extended (diameter ~90 kpc) ring around the central S0 galaxy. The HI data cube can be well modeled by a warped ring. The faint ionized gas in the inner parts of the galaxy is kinematically decoupled from the stars and instead appears to exhibit velocities consistent with the rotation of the HI ring at larger radius. The peak of the stellar ring, as seen in the optical and UV, is slightly displaced to the inside relative to the peak of the HI ring. We discuss the manner in which this offset could be caused by the propagation of a radial density wave through an existing stellar disk, perhaps triggered by a galaxy collision at the center of the disk, or possibly due to a spiral density wave set up at early times in a disk too hot to form a stellar bar. Gas accretion and resonance effects due to a bar which has since dissolved are also considered to explain the presence of the star forming ring seen in the GALEX and deep optical data.Comment: 48 pages, 16 figures, 4 tables. Accepted for publication in the Astronomical Journa

Deprojection of luminosity functions of galaxies in the Coma cluster

We use a simple analytic model to deproject 2-d luminosity functions (LF) of galaxies in the Coma cluster measured by Beijersbergen et al. 2002. We demonstrate that the shapes of the LFs change after deprojection. It is therefore essential to correct LFs for projection effects. The deprojected LFs of the central area have best-fitting Schechter parameters of M^{*}_U=-18.31^{+0.08}_{-0.08} and \alpha_U=-1.27^{+0.018}_{-0.018}, M^{*}_B=-19.79^{+0.14}_{-0.15} and \alpha_B=-1.44^{+0.016}_{-0.016} and M^{*}_r=-21.77^{+0.20}_{-0.28} and \alpha_r=-1.27^{+0.012}_{-0.012}. The corrections are not significant enough to change the previously observed trend of increasing faint end slopes with increasing distance to the cluster center. The weighted U, B, and r band slopes of the deprojected LFs show a slightly weaker steepening with increasing projected cluster radius.Comment: Accepted for publication in A&A as a Research Not

Fast outflow of neutral hydrogen in the radio galaxy 3C293

We report the detection of very broad HI absorption against the central regions of the radio galaxy 3C293. The absorption profile, obtained with the Westerbork Synthesis Radio Telescope, has a full width at zero intensity of about 1400 km/s and most of this broad absorption (~1000 km/s) is blueshifted relative to the systemic velocity. This absorption represents a fast outflow of neutral gas from the central regions of this AGN. Possible causes for such an outflow are discussed. We favour the idea that the interaction between the radio jet and the rich ISM produces this outflow. Some of the implications of this scenario are considered.Comment: 11 pages, 4 Figures To be published in: Astrophysical Journal Letter

Spin alignment of dark matter haloes in filaments and walls

The MMF technique is used to segment the cosmic web as seen in a cosmological N-body simulation into wall-like and filament-like structures. We find that the spins and shapes of dark matter haloes are significantly correlated with each other and with the orientation of their host structures. The shape orientation is such that the halo minor axes tend to lie perpendicular to the host structure, be it a wall or filament. The orientation of the halo spin vector is mass dependent. Low mass haloes in walls and filaments have a tendency to have their spins oriented within the parent structure, while higher mass haloes in filaments have spins that tend to lie perpendicular to the parent structure.Comment: 4 pages, 2 figure