Neutral Hydrogen Mapping of Virgo Cluster Blue Compact Dwarf Galaxies

A new installment of neutral hydrogen mappings of Blue Compact Dwarf galaxies, as defined by optical morphology, in and near the Virgo cluster is presented. The primary motivation was to search for outlying clouds of HI as potential interactive triggers of the enhanced star formation, and therefore the mapped galaxies were selected for large HI} mass, large optical diameter, and large velocity profile width. Approximately half the sample proved to have one or more small, low column density star-free companion clouds, either detached or appearing as an appendage in our maps, at resolution of order 4 kpc. Comparison is made to a sample of similarly mapped field BCD galaxies drawn from the literature; however, the Virgo cluster sample of mapped BCDs is still too small for conclusive comparisons to be made. We found, on the one hand, little or no evidence for ram pressure stripping nor, on the other, for extremely extended low column density HI envelopes. The HI rotation curves in most cases rise approximately linearly, and slowly, as far out as we can trace the gas.Comment: To appear in AJ, Dec. 200

The Fine Structure and Outskirts of DDO 154

Mapping of the HI disk of the isolated irregular galaxy DDO 154 with the C array of the Very Large Array and with the 3.2' upgraded Arecibo beam is presented. Our results show a truncation (or temporary drop) of the HI disk at a column density around 10^19 atoms cm^-2, consistent with theoretical expectations for the truncation produced by the extragalactic UV field. We also detect a marginally significant levelling off of the HI distribution along the continuation of the major axis at a column density near 2X10^18 atoms cm^-2. The VLA results show that the gas beyond ~6' in radius must be relatively smooth, with no structure larger in size than ~300 pc exhibiting a density contrast of a factor of 10 or more. However, there is considerable few-hundred-parsec scale structure in the gas disk at smaller radii, even well outside the regions where there are visible stars. Two prominent cavities well removed from any significant stellar populations are studied. While the energies required for evacuation are consistent with those produced by multiple supernovae, there is no visible trace of stars within a kpc of the center of the larger cavity, and the smaller of the two cavities is centered just outside the 26.5 mag arcsec^-2 B isophote. The velocity dispersion of the gas, measured within our 270 pc beam, is 7 to 8 km s^-1 throughout the disk (to 6' radius). This translates to a scaleheight of ~700 pc at the point where the rotation curve flattens, at a radius of ~4.5 kpc. Velocity profiles are well fit by single gaussians at all points.Comment: 14 pages, 2 tables, 13 figures, accepted for AJ Nov. 200

Complete Genome Sequence of the Complex Carbohydrate-Degrading Marine Bacterium, Saccharophagus degradans Strain 2-40T

The marine bacterium Saccharophagus degradans strain 2-40 (Sde 2-40) is emerging as a vanguard of a recently discovered group of marine and estuarine bacteria that recycles complex polysaccharides. We report its complete genome sequence, analysis of which identifies an unusually large number of enzymes that degrade >10 complex polysaccharides. Not only is this an extraordinary range of catabolic capability, many of the enzymes exhibit unusual architecture including novel combinations of catalytic and substrate-binding modules. We hypothesize that many of these features are adaptations that facilitate depolymerization of complex polysaccharides in the marine environment. This is the first sequenced genome of a marine bacterium that can degrade plant cell walls, an important component of the carbon cycle that is not well-characterized in the marine environment