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Публикации по объекту
The Radio Galaxy Populations of Nearby Northern Abell Clusters
We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radiogalaxies in 18 nearby Abell clusters. The listings extend from the coresof the clusters out to radii of 3 h-175 Mpc, whichcorresponds to 1.5 Abell radii and approximately 4 orders of magnitudein galaxy density. To create a truly useful catalog, we have collectedoptical spectra for nearly all of the galaxies lacking public velocitymeasurements. Consequently, we are able to discriminate between thoseradio galaxies seen in projection on the cluster and those that are inactuality cluster members. The resulting catalog consists of 329 clusterradio galaxies plus 138 galaxies deemed foreground or backgroundobjects, and new velocity measurements are reported for 273 of theseradio galaxies. The motivation for the catalog is the study of galaxyevolution in the cluster environment. The radio luminosity function is apowerful tool in the identification of active galaxies, as it isdominated by star-forming galaxies at intermediate luminosities andactive galactic nuclei (AGNs) at higher luminosities. The flux limit ofthe NVSS allows us to identify AGNs and star-forming galaxies down tostar formation rates less than 1 Msolar yr-1. Thissensitivity, coupled with the all-sky nature of the NVSS, allows us toproduce a catalog of considerable depth and breadth. In addition tothese data, we report detected infrared fluxes and upper limits obtainedfrom IRAS data. It is hoped that this database will prove useful in anumber of potential studies of the effect of environment on galaxyevolution. Based in part on observations obtained with the Apache PointObservatory 3.5 m telescope, which is owned and operated by theAstrophysical Research Consortium (ARC).
| The Einstein Two-Sigma Catalog: Silver Needles in the X-Ray Haystack
To facilitate the study of X-ray sources fainter than those contained inthe Einstein Medium-Sensitivity Survey (EMSS), we have constructed a newcatalog of sources and fluctuations exceeding 2 σ significance in2520 high-latitude Einstein IPCC images. We have employed various teststo validate our source-search algorithm for both high- and low-significance sources, and to identify and remove the small number ofspurious sources induced by our detection procedure. Based on the knownvignetting and background characteristics of the IPC and the measured X-ray log N-log S relation, we have modeled the number of real sourcesexpected in the catalog in order to evaluate its statistical propertiesbelow 4 σ significance. Our modeling suggests that ~13,000 sourcesin the catalog are real celestial X-ray sources, an increase of ~9100over the number found in previous analyses of the same IPC images. Wefind that not only is the reliability of the Two-Sigma Catalog afunction of source significance σ, it is a function of off-axisangle on the detector as well. The application of differentsignal-to-noise thresholds at different off-axis angles thus enables oneto tune the reliability of the catalog. The chief motivation forstudying large numbers of faint X-ray sources is to search for possiblenew components of the cosmic X-ray background. To select out realcelestial X-ray sources in the Two-Sigma Catalog, we apply astronomicalcatalogs at other wavelengths as filters. For example, thecross-correlation of the Two-Sigma Catalog with catalogs from surveys ofthe radio and infrared sky has yielded large samples of faint X-raysources that are ~90% reliable. Optical spectroscopy of 77 unidentifiedfaint X-ray sources has turned up several surprises, illustrating themerits of selecting X-ray sources using a variety of methods: high-redshift quasars (one at z = 4.30), which are absent in the EMSS, X-ray-luminous (L_x_ ~ 10^43^ ergs s^-1^) radio-loud elliptical galaxies withoptical spectra devoid of emission lines, and infrared-bright activegalactic nuclei whose optical spectra are dominated by starburst galaxyfeatures. Follow-up observations are scheduled to determine whether anyof these types of objects represent a previously unrecognized componentof the X-ray background.
| Redshifts for Fainter Galaxies in the First CFA Slice. III. To the Zwicky Catalog Limit
We have measured redshifts for 241 galaxies selected from the Zwickycatalog with magnitudes 15.6 or 15.7 in the region (26.5^deg^ <=32.5^deg^, 8^h^<= α <= 17^h^, 1950). This region is theoriginal CfA "Slice of the Universe," which was complete to 15.5; nownearly all Zwicky-catalog galaxies in the region have measuredredshifts. These somewhat fainter galaxies outline the same structuresas the brighter ones. By examining a sample of 27 galaxies within themost prominent void we find (1) the fraction of absorption-line galaxiesis typical of regions outside the cores of rich clusters; and (2) thelocal morphology- density relation holds within the globally underdensevoid.
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