The Interaction of Radio Sources and X-ray-Emitting Gas in Cooling Flows

Recent observations of the interactions between radio sources and the X-ray-emitting gas in cooling flows in the cores of clusters of galaxies are reviewed. The radio sources inflate bubbles in the X-ray gas, which then rise buoyantly outward in the clusters transporting energy to the intracluster medium (ICM). The bright rims of gas around the radio bubbles are cool, rather than hot, and do not show signs of being strongly shocked. Energy deposited into the ICM over the lifetime of a cluster through several outbursts of a radio source helps to account for at least some of the gas that is missing in cooling flows at low temperatures.Comment: Invited Review, "The Riddle of Cooling Flows in Galaxies and Clusters of Galaxies," Charlottesville, VA, USA. May 31 - June 4, 2003, see http://www.astro.virginia.edu/coolflow/ Editors: Reiprich, T. H., Kempner, J. C., and Soker, N.; 8 page

A Stellar Mass Threshold for Quenching of Field Galaxies

We demonstrate that dwarf galaxies (10^7 < M_stellar < 10^9 Msun) with no active star formation are extremely rare (<0.06%) in the field. Our sample is based on the NASA-Sloan Atlas which is a re-analysis of the Sloan Digital Sky Survey Data Release 8. We examine the relative number of quenched versus star forming dwarf galaxies, defining quenched galaxies as having no Halpha emission (EW_Halpha < 2 AA) and a strong 4000AA-break. The fraction of quenched dwarf galaxies decreases rapidly with increasing distance from a massive host, leveling off for distances beyond 1.5 Mpc. We define galaxies beyond 1.5 Mpc of a massive host galaxy to be in the field. We demonstrate that there is a stellar mass threshold of M_stellar < 1.0x10^9 Msun below which quenched galaxies do not exist in the field. Below this threshold, we find that none of the 2951 field dwarf galaxies are quenched; all field dwarf galaxies show evidence for recent star formation. Correcting for volume effects, this corresponds to a 1-sigma upper limit on the quenched fraction of 0.06%. In more dense environments, quenched galaxies account for 23% of the dwarf population over the same stellar mass range. The majority of quenched dwarf galaxies (often classified as dwarf elliptical galaxies) are within 2 virial radii of a massive galaxy, and only a few percent of quenched dwarf galaxies exist beyond 4 virial radii. Thus, for galaxies with stellar mass less than 1.0x10^9 Msun, ending star-formation requires the presence of a more massive neighbor, providing a stringent constraint on models of star formation feedback.Comment: 9 pages, 6 figures, accepted to Ap

Galaxy Cluster Environments of Radio Sources

Using the Sloan Digital Sky Survey (SDSS) and the FIRST (Faint Images of the Radio Sky at Twenty Centimeters) catalogs, we examined the optical environments around double-lobed radio sources. Previous studies have shown that multi-component radio sources exhibiting some degree of bending between components are likely to be found in galaxy clusters. Often this radio emission is associated with a cD-type galaxy at the center of a cluster. We cross-correlated the SDSS and FIRST catalogs and measured the richness of the cluster environments surrounding both bent and straight multi-component radio sources. This led to the discovery and classification of a large number of galaxy clusters out to a redshift of z ~ 0.5. We divided our sample into smaller subgroups based on their optical and radio properties. We find that FR I radio sources are more likely to be found in galaxy clusters than FR II sources. Further, we find that bent radio sources are more often found in galaxy clusters than non-bent radio sources. We also examined the environments around single-component radio sources and find that single-component radio sources are less likely to be associated with galaxy clusters than extended, multi-component radio sources. Bent, visually-selected sources are found in clusters or rich groups ~78% of the time. Those without optical hosts in SDSS are likely associated with clusters at even higher redshifts, most with redshifts of z > 0.7.Comment: 47 pages, 24 figures. Accepted by A

The Impact of Short-Term International Volunteers on the Capacity Development of a School for Students With Disabilities in the Caribbean

This qualitative study contributes to the field of international volunteerism by giving insight into the impact of short-term international volunteerism on the capacity development of a school for students with disabilities in the Caribbean. In the United States over one million people volunteer abroad annually, with 70-80% of these volunteers serving eight weeks or less (Lough, 2010). However, whether the international volunteers are having an impact on the capacity development of the population served remains to be seen. This study focused on an aspect of short-term international volunteerism that has largely been ignored – how short-term international volunteers impact the capacity development of host organizations. The study was guided by the United Nations Development Programme’s Framework for Measuring Capacity Development which was utilized as the theoretical framework. This case study found that five years after an educational program was conducted by short-term international volunteers at a school for students with disabilities in the Caribbean, there was a noted impact on capacity development. Teachers were continuing to use some of the strategies taught by the international volunteers as well as use some of the resources provided. Recommendations for further studies are provided as well as the study’s implications for the design of short-term international volunteer projects

Where’s My Money? Using Experiential Learning to Increase Financial Capability

This paper looks at how experiential learning is being implemented at Texas A&M University-San Antonio to expand the financial capability of students; and how the project engages students and parents at local school districts. Presented below is the purpose, structure, funding, learning, and assessment of the program that can serve as insight into other campuses that may want to implement something similar