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An Hα survey of cluster galaxies - V. Cluster-field comparison for early-type galaxies
We have extended our Hα objective prism survey of eightlow-redshift clusters (viz. Abell 262, 347, 400, 426, 569, 779, 1367 and1656) to include a complete sample of early-type galaxies within 1.5Abell radii of the cluster centres. Of the 379 galaxies surveyed, 3 percent of E, E-S0 galaxies, 6 per cent of S0 galaxies, and 9 per cent ofS0/a galaxies were detected in emission. From a comparison of clusterand supercluster field galaxies, we conclude that the frequency ofemission-line galaxies (ELGs; Wλ>= 20 Å) issimilar for field and cluster early-type galaxies. A similar result haspreviously been obtained for galaxies of types Sa and later. Together,these results confirm the inference of Biviano et al. that the relativefrequency of ELGs in clusters and the field can be entirely accountedfor by the different mix of morphological types between the differingenvironments, and that, for galaxies of a given morphological type, thefraction of ELGs is independent of environment. Detected emission isclassified as `compact' or `diffuse', identified as circumnuclearstarburst or active galactic nucleus (AGN) emission and disc emission,respectively. By comparing spectroscopic data for cluster early-typeELGs with data for field galaxies from the Palomar spectroscopic surveyof nearby galactic nuclei, we demonstrate that there is modest evidencefor an enhancement of compact HII emission relative to AGN emission inthe early-type cluster ELGs as compared to the field. For the clusterearly-type galaxies, compact HII emission correlates strongly with adisturbed morphology. This suggests that, as for later-type clustergalaxies, this enhanced compact HII emission can readily be explained asan enhancement of circumnuclear starburst emission due to gravitationaltidal interactions, most likely caused by subcluster merging and otheron-going processes of cluster virialization.
| Evolution of Star-forming and Active Galaxies in Nearby Clusters
We have used optical spectroscopy to investigate the active galaxypopulations in a sample of 20 nearby Abell clusters. The targets wereidentified on the basis of 1.4 GHz radio emission, which identifies themas either active galactic nuclei (AGNs) or galaxies forming stars atrates comparable to or greater than that of the Milky Way. The spectrawere used to characterize the galaxies via their emission and absorptionfeatures. The spectroscopy results reveal a significant population ofstar-forming galaxies with large amounts of nuclear dust extinction.This extinction eliminates bluer emission lines such as [O II] from thespectra of these galaxies, meaning their star formation could easily beoverlooked in studies that focus on such features. Around 20% of thecluster star-forming galaxies have spectra of this type. The radialdistributions of active galaxies in clusters show a strong segregationbetween star-forming galaxies and AGNs, with star-forming galaxiesbroadly distributed and AGNs preferentially in the cluster cores. Theradial distribution of the dusty star-forming galaxies is more centrallyconcentrated than the star-forming galaxies in general, which arguesthat they are a consequence of some cluster environmental effect.Furthermore, we note that such galaxies may be identified using their4000 Å break strengths. We find that discrepancies in reportedradio luminosity functions for AGNs are likely the result ofclassification differences. There exists a large population of clustergalaxies whose radio fluxes, far-infrared fluxes, and optical magnitudessuggest their radio emission may be powered by stars yet whose spectralack emission lines. Understanding the nature of these galaxies iscritical to assessing the importance of AGNs in the radio luminosityfunction at low luminosities. We also find that regardless of thispopulation, the crossover point where the radio luminosity function iscomposed equally of star-forming galaxies and AGNs occurs at lowerluminosities in clusters than in the field. This is likely a simpleconsequence of the reduction in star formation in cluster galaxies andthe morphological mix in clusters compared with the field.Based in part on observations obtained with the Apache Point Observatory(APO) 3.5 m telescope, which is owned and operated by the AstrophysicalResearch Consortium.
| 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).
| An Hα survey of eight Abell clusters: the dependence of tidally induced star formation on cluster density
We have undertaken a survey of Hα emission in a substantiallycomplete sample of CGCG galaxies of types Sa and later within 1.5 Abellradii of the centres of eight low-redshift Abell clusters (Abell 262,347, 400, 426, 569, 779, 1367 and 1656). Some 320 galaxies weresurveyed, of which 116 were detected in emission (39 per cent ofspirals, 75 per cent of peculiars). Here we present previouslyunpublished data for 243 galaxies in seven clusters. Detected emissionis classified as `compact' or `diffuse'. From an analysis of the fullsurvey sample, we confirm our previous identification of compact anddiffuse emission with circumnuclear starburst and disc emissionrespectively. The circumnuclear emission is associated either with thepresence of a bar, or with a disturbed galaxy morphology indicative ofongoing tidal interactions (whether galaxy-galaxy, galaxy-group, orgalaxy-cluster). The frequency of such tidally induced (circumnuclear)starburst emission in spirals increases from regions of lower to higherlocal galaxy surface density, and from clusters with lower to highercentral galaxy space density. The percentages of spirals classed asdisturbed and of galaxies classified as peculiar show a similar trend.These results suggest that tidal interactions for spirals are morefrequent in regions of higher local density and for clusters with highercentral galaxy density. The prevalence of such tidal interactions inclusters is expected from recent theoretical modelling of clusters witha non-static potential undergoing collapse and infall. Furthermore, inaccord with this picture, we suggest that peculiar galaxies arepredominantly ongoing mergers. We conclude that tidal interactions arelikely to be the main mechanism for the transformation of spirals to S0sin clusters. This mechanism operates more efficiently in higher densityenvironments, as is required by the morphological type-local surfacedensity (T-Σ) relation for galaxies in clusters. For regions ofcomparable local density, the frequency of tidally induced starburstemission is greater in clusters with higher central galaxy density. Thisimplies that, for a given local density, morphological transformation ofdisc galaxies proceeds more rapidly in clusters of higher central galaxydensity. This effect is considered to be the result of subclustermerging, and could account for the previously considered anomalousabsence of a significant T-Σ relation for irregular clusters atintermediate redshift.
| Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.
| Redshift and Optical Properties for S Statistically Complete Sample of Poor Galaxy Clusters
From the poor cluster catalog of White et al. (1996), we define a sampleof 71 optically-selected poor galaxy clusters. The surface-densityenhancement we require for our clusters falls between that of the looseassociations of Turner & Gott [AJ, 91,204(1976)] and the Hicksoncompact groups [Hickson, ApJ, 255, 382(1982)]. We review the selectionbiases and determine the statistical completeness of the sample. Forthis sample, we report new velocity measurements made with the ARC 3.5-mDual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiberspectrograph. Combining our own measurements with those from theliterature, we examine the velocity distributions, velocity dispersions,and ID velocity substructure for our poor cluster sample, and compareour results to other poor cluster samples. We find that approximatelyhalf of the sample may have significant ID velocity substructure. Theoptical morphology, large-scale environment, and velocity field of manyof these clusters are indicative of young, dynamically evolving systems.In future papers, we will use this sample to derive the poor clusterx-ray luminosity function and gas mass function, and will examine theoptical/x-ray properties of the clusters in more detail.
| An image database. II. Catalogue between δ=-30deg and δ=70deg.
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
| Corrections to the Reference Catalogue of Bright Galaxies (Third List)
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972PASP...84..462C&db_key=AST
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