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ALABAMA University Libraries THE UNIVERSITY OF ALABAMA University Libraries Radio-Selected Galaxies in Very Rich Clusters at z ≤ 0.25. I. Multiwavelength Observations and Data Reduction Techniques William C. Keel – University of Alabama et al. Deposited 09/26/2018 Citation of published version: Keel, W., et al. (2003): Radio-Selected Galaxies in Very Rich Clusters at z ≤ 0.25. I. Multiwavelength Observations and Data Reduction Techniques. The Astrophysical Journal Supplement Series. 146(2) DOI: 10.1086/368014 © 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. The Astrophysical Journal Supplement Series, 146:267–298, 2003 June E # 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. RADIO-SELECTED GALAXIES IN VERY RICH CLUSTERS AT z 0.25. I. MULTIWAVELENGTH OBSERVATIONS AND DATA REDUCTION TECHNIQUES G. E. Morrison,1,2,3,4,5 F. N. Owen1,2 M. J. Ledlow,1,6 W. C. Keel,1,7 J. M. Hill,8 W. Voges,9 and T. Herter10 Received 2000 September 5; accepted 2002 December 5 ABSTRACT Radio observations were used to detect the ‘‘ active ’’ galaxy population within rich clusters of galaxies in a nonbiased manner that is not plagued by dust extinction or the K-correction. We present wide-field radio, optical (imaging and spectroscopy), and ROSAT All-Sky Survey (RASS) X-ray data for a sample of 30 very 22 rich Abell (R 2) clusters with z 0:25. The VLA radio data samples the ultrafaint radio (L1:4 2 Â 10 W À1 Hz ) galaxy population within these extremely rich clusters for galaxies with MR À21. This is the largest sample of low-luminosity 20 cm radio galaxies within rich Abell clusters collected to date. À1 The radio-selected galaxy sample represents the starburst (star formation rate 5 M yr ) and active galactic nuclei populations contained within each cluster. Archival and newly acquired redshifts were used to verify cluster membership for most (95%) of the optical identifications. Thus, we can identify all the star- bursting galaxies within these clusters, regardless of the level of dust obscuration that would affect these galaxies being identified from their optical signature. Cluster sample selection, observations, and data reduction techniques for all wavelengths are discussed. Subject headings: galaxies: clusters: general — galaxies: evolution — galaxies: starburst — radio continuum: galaxies On-line material: machine-readable table 1. INTRODUCTION galaxies in rich clusters may be related to hierarchical large- scale structure (LSS) formation and the accretion of field Optical studies of rich clusters to determine the star for- mation rates (SFRs) of their cluster members have been galaxies. Where the starburst population occurs within the cluster environment yields clues to the origin of the perturb- ongoing since the early photometric study by Butcher & ing mechanism. To study this ‘‘ active ’’ galaxy population Oemler (1978) over 20 years ago. Such studies have sought to recover the star formation properties of galaxies in rich (starburst/active galactic nucleus) requires a method that will detect this population in a unbiased manner. clusters via optical photometry, spectroscopy, and more Radio observations allow one to detect starbursts and recently from Hubble Space Telescope (HST) morphologi- active galactic nuclei (AGNs) without the drawbacks of cal studies. The discovery by Butcher & Oemler (1978, 1984) optical observations, such as dust attenuation and the opti- of the increased fraction of blue galaxies within the core of cal K-correction. In principle, far-IR (FIR) observations selected rich regular clusters indicated significant evolution would detect reemission from the dust, of the UV photons in the SFR and/or galaxy type within the central regions of emitted by the OB stars formed in a massive starburst. Until these massive systems over the last 5 Gyr (assuming the launch of SIRTF, FIR instruments will not have the sen- H ¼ 75 km sÀ1, q ¼ 0:1) or zd0:4. The change in SFR of 0 0 sitivity or the resolution to be effective. However, the well- known FIR-radio continuum correlation based on ongoing 1 Visiting Astronomer, Kitt Peak National Observatory (KPNO), star formation allows easier detection of starbursting sys- National Optical Astronomy Observatory, operated by the Association of tems in distant clusters. Studies of the local radio luminosity Universities for Research in Astronomy, Inc., under contract with the function (e.g., Condon et al. 1991), indicate that the star- National Science Foundation. 2 National Radio Astronomy Observatory, P.O. Box O, Socorro, bursting and spiral galaxy population dominate the 20 cm 23 À1 NM 87801; The National Radio Astronomy Observatory is operated by radio luminosity function below 10 WHz . Associated Universities, Inc., under a cooperative agreement with the Radio selection of cluster members by their low radio National Science Foundation; [email protected]. luminosity yields two kinds of objects—weak AGNs and 3 Also Department of Physics and Astronomy, University of New objects with active star formation. The FIR-radio correla- Mexico, Albuquerque, NM 87131. 4 Vanguard Research, Inc., Scotts Valley, CA 95066. tion ties the nonthermal radio emission to the ongoing star 5 Current address: California Institute of Technology, IPAC, M/S 100- formation (Condon 1992). In starbursts, radio emission 22, Pasadena, CA 91125; [email protected]. fades faster than blue starlight, so clusters with large num- 6 Gemini Observatory, Southern Operations Center, AURA, Casilla ber of radio sources will preferentially be those that have 603, La Serena, Chile; [email protected]. 7 Department of Physics and Astronomy, University of Alabama, had a large numbers of recent or ongoing starbursts. This Tuscaloosa, AL 35487; [email protected]. may indicate the entry of a new group of galaxies into the 8 Steward Observatory, University of Arizona, Tucson, AZ 85721; cluster with star formation in its members. [email protected]. This paper is the first in a series studying the ultrafaint 9 Max-Planck-Institut fu¨r Extraterrestrische Physik, Postfach 1312, radio-selected galaxy populations associated with rich clus- D-85741 Garching bei Mu¨nchen, Germany; [email protected]. 10 202 Space Sciences Building, Cornell University, Ithaca, NY 14853- ters of galaxies as a function of redshift. This paper presents 6801; [email protected]. the radio, optical, and X-ray data for a sample of 30 very 267 268 MORRISON ET AL. Vol. 146 rich clusters (Abell richness class R 2) with z 0:25 2.1. The Redshift Samples selected from the catalog of Abell et al. (1989, hereafter The 0:02 z 0:07 sample.—The lowest redshift sample ACO). The VLA offers a large field of view (300) permit- contains the 10 richest nearby clusters11 (z 0:07). Here the ting us to go out to 2.5 Mpc radius from the cluster core. 1.4 GHz, 4500 resolution, D-array NRAO VLA sky survey This allows us to detect infalling starbursting field galaxies (NVSS) provided sufficient sensitivity to survey the richest and any supercluster induced effects such as cluster-cluster local clusters out to a radius of 2.5 Mpc and down to our mergers. Our detection limit of 2 Â 1022 WHzÀ1 allows limiting luminosity of about 2 Â 1022 WHzÀ1. However, detection of galaxies undergoing moderate to vigorous star since the local clusters were not as rich as the clusters in our formation with star formation rates 5 M yrÀ1. z ¼ 0:4 sample, we must go to a higher redshifts to find In this data paper, we discuss selection of the cluster sam- clusters of comparably high richness. ple along with the multiwavelength observations, and the The 0:10 z 0:18 sample.—This low-redshift sample data reduction techniques for a sample of the richest Abell of 14 clusters provides the extremely rich clusters that was clusters from 0:02 z 0:25. These clusters were chosen to lacking in the local sample and were comparable to the be as rich or richer than our four rich z ¼ 0:4 clusters (Abell z ¼ 0:40 sample. This provides a baseline useful for deter- 370, Cl 0024+1654, Cl 0939+4713, and Cl 1447+2619), mining the dependence of redshift on cluster properties. which will be presented in future papers. We also present a The 0:20 z 0:25 sample.—Our intermediate-redshift radio-selected sample of starburst and AGN galaxies within sample contains 12 very rich, X-ray luminous clusters culled these 30 rich clusters. Most of the detected galaxies had from the ACO catalog. The two clusters that provided the follow-up spectroscopy to verify cluster membership. original motivation for this study, A2125 and A2645 were Future papers analyze the radio properties (Morrison & included in this sample. Some of these clusters show a signif- Owen 2003, hereafter Paper II), the optical properties of the icant increase in their blue galaxy population compared to clusters (G. E. Morrison, F. N. Owen, & M. J. Ledlow 2003, local-epoch rich clusters. One of these clusters was A2125, in preparation, hereafter Paper III), and spectroscopy of the which also showed a substantially larger radio-selected gal- optical counterparts (G. E. Morrison, F. N. Owen, M. J. axy population from 1022.3–1023 WHzÀ1 compared with Ledlow, J. Hill, & T. Herter 2004, in preparation, hereafter A2645 (Owen et al. 1999). Paper IV). Deep (15 hr) wide-field VLA B-array observa- The z ¼ 0:4 sample.—This sample will be presented in a tions of Cl 0939+4713 at z 0:41 and subsequent spectro- ¼ future paper. scopic analysis of the radio-selected galaxy population will appear in Paper V (G. E. Morrison et al. 2003, in prepara- 2.2. Cluster Membership Requirements tion). HST NICMOS and WFPC2 results of several of the radio-selected galaxies in Cl 0939+4713 were discussed in For an identification to be considered a cluster member, it Smail et al.
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