Virgo Early-Type Dwarfs in ALFALFA

Early-type dwarf galaxies dominate cluster populations, but their formation and evolutionary histories are poorly understood. The ALFALFA (Arecibo Legacy Fast ALFA) survey has completed observations of the Virgo Cluster in the declination range of 6 - 16 degrees. Less than 2% of the early-type dwarf population is detected, a significantly lower fraction than reported in previous papers based on more limited samples. In contrast ~30 of the irregular/BCD dwarf population is detected. The detected early-type galaxies tend to be located in the outer regions of the cluster, with a concentration in the direction of the M Cloud. Many show evidence for ongoing/recent star formation. Galaxies such as these may be undergoing morphological transition due to cluster environmental effects.Comment: 2 pages. To be published in proceedings of IAU Symposium 244: 'Dark Galaxies and Lost Baryons', J. I. Davies & M. D. Disney. eds., Cambridge University Pres

Observations of Stripped Edge-on Virgo Cluster Galaxies

We present observations of highly inclined, HI deficient, Virgo cluster spiral galaxies. Our high-resolution VLA HI observations of edge-on galaxies allow us to distinguish extraplanar gas from disk gas. All of our galaxies have truncated H-alpha disks, with little or no disk gas beyond a truncation radius. While all the gas disks are truncated, the observations show evidence for a continuum of stripping states: symmetric, undisturbed truncated gas disks indicate galaxies that were stripped long ago, while more asymmetric disks suggest ongoing or more recent stripping. We compare these timescale estimates with results obtained from two-dimensional stellar spectroscopy of the outer disks of galaxies in our sample. One of the galaxies in our sample, NGC 4522 is a clear example of active ram-pressure stripping, with 40% of its detected HI being extraplanar. As expected, the outer disk stellar populations of this galaxy show clear signs of recent (and, in fact, ongoing) stripping. Somewhat less expected, however, is the fact that the spectrum of the outer disk of this galaxy, with very strong Balmer absorption and no observable emission, would be classified as ``k+a'' if observed at higher redshift. Our observations of NGC 4522 and other galaxies at a range of cluster radii allow us to better understand the role that clusters play in the structure and evolution of disk galaxies.Comment: 4 pages, 2 figures, to appear in the proceedings of the Island Universes conference held in Terschelling, Netherlands, July 2005, ed. R. de Jong, version with high resolution figures can be downloaded from ftp://ftp.astro.yale.edu/pub/hugh/papers/iu_crowl_h.ps.g

The Trouble with Hubble Types in the Virgo Cluster

Quantitative measures of central light concentration and star formation activity are derived from R and Halpha surface photometry of 84 bright S0-Scd Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a good correlation between these two parameters and assigned Hubble types. In the Virgo Cluster, the correlation between central light concentration and star formation activity is significantly weaker. Virgo Cluster spirals have systematically reduced global star formation with respect to isolated spirals, with severe reduction in the outer disk, but normal or enhanced activity in the inner disk. Assigned Hubble types are thus inadequate to describe the range in morphologies of bright Virgo Cluster spirals. In particular, spirals with reduced global star formation activity are often assigned misleading early-type classifications, irrespective of their central light concentrations. 45+-25% of the galaxies classified as Sa in the Virgo Cluster sample have central light concentrations more characteristic of isolated Sb-Sc galaxies. The misleading classification of low concentration galaxies with low star formation rates as early-type spirals may account for part of the excess of `early-type' spiral galaxies in clusters. Thus the morphology-density relationship is not all due to a systematic increase in the bulge-to-disk ratio with environmental density.Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2 Postscript (embedded) figures. Also available at http://www.astro.yale.edu/koopmann/preprint.htm

Uniform Interpolation and Forgetting for ALC Ontologies with ABoxes

Uniform interpolation and the dual task of forgetting restrict the ontology to a specified subset of concept and role names. This makes them useful tools for ontology analysis, ontology evolution and information hiding. Most previous research focused on uniform interpolation of TBoxes. However, especially for applications in privacy and information hiding, it is essential that uniform interpolation methods can deal with ABoxes as well. We present the first method that can compute uniform interpolants of any ALC ontology with ABoxes. ABoxes bring their own challenges when computing uniform interpolants, possibly requiring disjunctive statements or nominals in the resulting ABox. Our method can compute representations of uniform interpolants in ALCO. An evaluation on realistic ontologies shows that these uniform interpolants can be practically computed, and can often even be presented in pure ALC

An Atlas of H-alpha and R Images and Radial Profiles of 29 Bright Isolated Spiral Galaxies

Narrow-band H-alpha+[NII] and broadband R images and surface photometry are presented for a sample of 29 bright (M_B < -18) isolated S0-Scd galaxies within a distance of 48 Mpc. These galaxies are among the most isolated nearby spiral galaxies of their Hubble classifications as determined from the Nearby Galaxies Catalog (Tully 1987a).Comment: To appear in Astrophysical Journal Supplement Series. 17 pages, including 8 atlas pages in JPEG format. Version with high resolution figures available at http://www1.union.edu/~koopmanr/preprints.htm