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

Metal enrichment processes

There are many processes that can transport gas from the galaxies to their environment and enrich the environment in this way with metals. These metal enrichment processes have a large influence on the evolution of both the galaxies and their environment. Various processes can contribute to the gas transfer: ram-pressure stripping, galactic winds, AGN outflows, galaxy-galaxy interactions and others. We review their observational evidence, corresponding simulations, their efficiencies, and their time scales as far as they are known to date. It seems that all processes can contribute to the enrichment. There is not a single process that always dominates the enrichment, because the efficiencies of the processes vary strongly with galaxy and environmental properties.Comment: 18 pages, 8 figures, accepted for publication in Space Science Reviews, special issue "Clusters of galaxies: beyond the thermal view", Editor J.S. Kaastra, Chapter 17; work done by an international team at the International Space Science Institute (ISSI), Bern, organised by J.S. Kaastra, A.M. Bykov, S. Schindler & J.A.M. Bleeke

Lethe::Saturation-based reasoning for non-standard reasoning tasks

Abstract. We present the saturation-based reasoning system Lethe. Lethe is a tool that can be used for uniform interpolation, forgetting, TBox abduction and logical dierence. To solve these problems, Lethe uses saturation-based reasoning to eliminate certain symbols from an ontology, such that entailments in the remaining vocabulary are preserved. This is known as forgetting or uniform interpolation. Lethe is an implementation of our forgetting methods for various expressive description logics, and can be used as a Java library and as a standalone tool for the mentioned reasoning tasks. We give a high level description of the calculi used by Lethe, describe the reasoning algorithm implemented in Lethe, and give an evaluation of the system on realistic ontologies

Count and Forget: Uniform Interpolation of SHQ-Ontologies

Abstract. We propose a method for forgetting concept symbols and non-transitive roles symbols of SHQ-ontologies, or for computing uni-form interpolants in SHQ. Uniform interpolants restrict the symbols occuring in an ontology to a specified set, while preserving all logical entailments that can be expressed using this set in the description logic under consideration. Uniform interpolation has applications in ontology reuse, information hiding and ontology analysis, but so far no method for computing uniform interpolants for expressive description logics with number restrictions has been developed. Our results are not only inter-esting because they allow to compute uniform interpolants of ontologies using a more expressive language. Using number restrictions also allows to preserve more information in uniform interpolants of ontologies in less complex logics, such as ALC or EL. The presented method computes uni-form interpolants on the basis of a new resolution calculus for SHQ. The output of our method is expressed using SHQµ, which is SHQ extended with fixpoint operators, to always enable a finite representation of the uniform interpolant. If the uniform interpolant uses fixpoint operators, it can be represented in SHQ without fixpoints operators using additional concept symbols or by approximation.

Virgo Filaments. II. Catalog and First Results on the Effect of Filaments on Galaxy Properties

Virgo is the nearest galaxy cluster; it is thus ideal for studies of galaxy evolution in dense environments in the local universe. It is embedded in a complex filamentary network of galaxies and groups, which represents the skeleton of the large-scale Laniakea supercluster. Here we assemble a comprehensive catalog of galaxies extending up to ∼12 virial radii in projection from Virgo to revisit the cosmic-web structure around it. This work is the foundation of a series of papers that will investigate the multiwavelength properties of galaxies in the cosmic web around Virgo. We match spectroscopically confirmed sources from several databases and surveys including HyperLeda, NASA Sloan Atlas, NASA/IPAC Extragalactic Database, and ALFALFA. The sample consists of ∼7000 galaxies. By exploiting a tomographic approach, we identify 13 filaments, spanning several megaparsecs in length. Long >17 h -1 Mpc filaments, tend to be thin (<1 h -1 Mpc in radius) and with a low-density contrast (<5), while shorter filaments show a larger scatter in their structural properties. Overall, we find that filaments are a transitioning environment between the field and cluster in terms of local densities, galaxy morphologies, and fraction of barred galaxies. Denser filaments have a higher fraction of early-type galaxies, suggesting that the morphology-density relation is already in place in the filaments, before galaxies fall into the cluster itself. We release the full catalog of galaxies around Virgo and their associated properties. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

The Arecibo Pisces-Perseus Supercluster Survey. I. Harvesting ALFALFA

We report a multi-objective campaign of targeted 21 cm H i line observations of sources selected from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey and galaxies identified by their morphological and photometric properties in the Sloan Digital Sky Survey. The aims of this program have been (1) to confirm the reality of some ALFALFA sources whose enigmatic nature suggest additional multiwavelength observations; (2) to probe the low signal-to-noise ratio (S/N) regime, below the ALFALFA reliability limit; and (3) to explore the feasibility of using optical morphology, color, and surface brightness to identify gas-rich objects in the region of the Pisces-Perseus Supercluster (PPS) whose H i fluxes are below the ALFALFA sensitivity limit at that distance. As expected, the reliability of ALFALFA detections depends strongly on the S/N of the H i line signal and its coincidence with a probable stellar counterpart identified by its optical properties, suggestive of ongoing star formation. The identification of low-mass, star-forming populations enables targeted H i line observations to detect galaxies with H i line fluxes below the ALFALFA sensitivity limits in fixed local volumes (D < 100 Mpc). The method explored here serves as the basis for extending the sample of gas-bearing objects as part of the ongoing Arecibo Pisces-Perseus Supercluster Survey (APPSS). © 2019. The American Astronomical Society. All rights reserved.This work has been supported by NSF grants AST-1211005, AST-1637339, and AST-1637271. R.G., M.P.H., L.L., and M.G.J. acknowledge support from NSF grants AST-1107390 and AST-1714828 and by grants from the Brinson Foundation. M.G.J. acknowledges support from the grant AYA2015-65973-C3-1-R (MINECO/FEDER, UE).Peer Reviewe