THE ASTROPHYSICAL JOURNAL SUPPLEMENT SERIES, 126:209È269, 2000 February ( 2000. The American Astronomical Society. All rights reserved. Printed in U.S.A. THE BRIGHT SHARC SURVEY: THE CLUSTER CATALOG1 A. K. ROMER2 AND R. C. NICHOL3,4 Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213; romer=cmu.edu, nichol=cmu.edu B. P. HOLDEN2,3 Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637; holden=oddjob.uchicago.edu M. P. ULMER AND R. A. PILDIS Department of Physics and Astronomy, Northwestern University, 2131 North Sheridan Road, Evanston, IL 60207; ulmer=ossenu.astro.nwu.edu A. J. MERRELLI2 Department of Physics, Carnegie Mellon University, 5000. Forbes Avenue, Pittsburgh, PA 15213; merrelli=andrew.cmu.edu C. ADAMI4 Department of Physics and Astronomy, Northwestern University, 2131 North Sheridan Road, Evanston, IL 60207;adami=lilith.astro.nwu.edu; and Laboratoire d Astronomie Spatiale, Traverse du Siphon, 13012 Marseille, France D. J. BURKE3 AND C. A. COLLINS3 Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, L41 1LD, UK; djb=astro.livjm.ac.uk, cac=astro.livjm.ac.uk A. J. METEVIER UCO/Lick Observatory, University of California, Santa Cruz, CA 95064; anne=ucolick.org R. G. KRON Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637; rich=oddjob.uchicago.edu AND K. COMMONS2 Department of Physics and Astronomy, Northwestern University, 2131 North Sheridan Road, Evanston, IL 60207; commons=lilith.astro.nwu.edu Received 1999 April 12; accepted 1999 August 23 ABSTRACT We present the Bright SHARC (Serendipitous High-Redshift Archival ROSAT Cluster) Survey, which is an objective search for serendipitously detected extended X-ray sources in 460 deep ROSAT PSPC pointings. The Bright SHARC Survey covers an area of 178.6 deg2 and has yielded 374 extended sources. We discuss the X-ray data reduction, the candidate selection and present results from our on- going optical follow-up campaign. The optical follow-up concentrates on the brightest 94 of the 374 extended sources and is now 97% complete. We have identiÐed 37 clusters of galaxies, for which we present redshifts and luminosities. The clusters span a redshift range of 0.0696 \ z \ 0.83 and a lumi- ] 44 ~1 \ ~1 ~1 nosity range of0.065 \ L X \ 8.3 10 ergs s [0.5È2.0 keV] (assumingH0 50 km s Mpc and q \ 0.5). Twelve of the clusters have redshifts greater than z \ 0.3, eight of which are at luminosities 0 \ ] 44 ~1 brighter thanL X 3 10 ergs s . Seventeen of the 37 optically conÐrmed Bright SHARC clusters have not been listed in any previously published catalog. We also report the discovery of three candidate ““ fossil groups ÏÏ of the kind proposed by Ponman et al. Subject headings: catalogs È galaxies: clusters: general È galaxies: distances and redshifts È surveys È X-rays: galaxies INTRODUCTION 1. persion in the values of)m derived from measurements of the cluster number density; e.g.,) \ 0.2`0.3 (Bahcall & Clusters of galaxies play a key role in constraining \ `0.3 m ~0.1 \ Fan 1998),)m 0.4~0.2 (Borgani et al. 1999), )m cosmological models. It has been shown (e.g., Oukbir & 0.5B0.14 (Henry 1997),) \ 0.85B0.2 (Sadat et al. 1998), Blanchard 1992; Carlberg et al. 1997; Henry 1997; Sadat, \ `0.36 m )m 0.96~0.32 (Reichart et al. 1999). Blanchard, & Oukbir 1998; Viana & Liddle 1999) that mea- To fully exploit clusters as cosmological tools one needs surements of the cluster number density, and its evolution, to have access to large, objectively selected, cluster catalogs play an important role in the derivation of the mean mass that cover a wide redshift range. Most cluster catalogs con- density of the universe,)m. At present, there is a large dis- structed prior to 1990 had a very limited redshift range and were not constructed in an objective manner (e.g., Abell 1 Based on data taken at the European Southern Observatory, Kitt 1958; Abell, Corwin, & Olowin 1989). However, recent Peak National Observatory, Cerro Tololo Inter-American Observatory, developments, such as CCD mosaic cameras, optical plate Canada-France-Hawaii, and Apache Point Observatory. digitizers, and imaging X-ray satellites, have resulted in a 2 Visiting Astronomer, Kitt Peak National Observatory. KPNO is growing number of high-quality cluster catalogs. These operated by AURA, Inc., under contract to the National Science Founda- tion. include optically selected cluster samples derived from digi- 3 Visiting Astronomer, European Southern Observatory. tized plate material, e.g., the EDCC (Lumsden et al. 1992) 4 Visiting Astronomer, Canada-France-Hawaii Telescope. and the APM (Dalton et al. 1994), or from CCD imaging 209 210 ROMER ET AL. Vol. 126 surveys, e.g., the PDCS (Postman et al. 1996) and the ESO unabsorbed Ñux (observer frame) and luminosity (rest Imaging Survey (Lobo et al. 1998). X-ray selected cluster frame) in the [0.5È2.0 keV] energy band in units of 10~13 samples derived from imaging X-ray satellite data include ergs s~1 cm~2 and 1044 ergs s~1, respectively. those from the Einstein mission, e.g., the EMSS cluster sample (Gioia et al. 1990), and those from the ROSAT 2. TRANSFER AND REDUCTION OF ROSAT PSPC (Tru mper 1993) mission. POINTING DATA The various ROSAT cluster catalogs divide into two categories; those based on ROSAT All-Sky Survey (RASS) The pointed PSPC data used in the construction of the data and those based on ROSAT pointing data. The former Bright SHARC was obtained from the HEASARC ROSAT category includes the SRCS (Romer 1995), XBACS (Ebeling data archive using an automated FTP process over a period et al. 1996), BCS (Ebeling et al. 1998), REFLEX (Bo hringer of two years starting in 1995 June. The criteria used to select et al. 1998; De Grandi et al. al 1999a) and NEP (Gioia et al. data from the archive were (i) a listed exposure time greater 1999; Henry et al. 1997) surveys. Examples of surveys based than 10 ks and (ii) an absolute Galactic latitude greater than on ROSAT pointing data are the SHARC (Collins et al. 20¡. Based on these criteria, 638 PSPC pointings were trans- 1997); RIXOS (Castander et al. 1995); RDCS (Rosati et al. ferred to local machines and then reduced using a pipeline 1998); WARPS (Jones et al. 1998) and 160 deg2 (Vikhlinin processing based on the Extended Source Analysis Software et al. 1998a) surveys. The ROSAT instrument of choice (ESAS) package (Snowden et al. 1994). for cluster surveys has been the PSPC, which combines An overview of our pipeline is as follows. First, the raw imaging capabilities with a large Ðeld of view (2¡ in data were sorted into good and bad time intervals. Bad diameter), low background contamination and some spec- intervals were deÐned as those in which the background tral resolution. The angular resolution of the ROSAT level was higher than 170 counts s~1. Data obtained during PSPC is better than that of Einstein, allowing one to take bad intervals were discarded. The remaining data were advantage of the extended nature of cluster emission to binned, as a function of position, into seven di†erent energy distinguish clusters from X-ray point sources, e.g., active bandsÈwhich Snowden et al. (1994) deÐne as R1 through galactic nuclei (AGNs) and quasars. Moreover, the R7Èto produce seven 512 ] 512 pixel maps with a pixel enhanced sensitivity of ROSAT over Einstein means that scale of14A.947. The Ðve highest energy bands, R3 through ROSAT cluster surveys can reach fainter Ñux limits than the R7, were then co-added to produce a hard band [0.4È2.0 EMSS. keV] count rate map for each pointing. Accompanying each The RASS surveys have yielded several important count rate map was a count rate uncertainty map and a insights into the clustering properties (Romer et al. 1994) vignetting corrected exposure map. and evolution (Ebeling et al. 1997; De Grandi et al. 1999b) For each of the 638 pointings reduced by the ESAS pipe- of the z \ 0.3 cluster population. At higher redshifts, the line, the ROSAT pointing name (col. [1]), the J2000 posi- ROSAT pointing data surveys have shown that there is no tion (cols. [2] and [3]), Galactic latitude in degrees (b, col. evidence for evolution in the cluster population at lumi- [4]), the exposure time in seconds (col. [5]) and pointing \ ] 44 ~1 nosities fainter thanL X 5 10 ergs s [0.5È2.0 keV] target (col. [6]) are listed in Tables 4 and 5 (see Appendix A and redshifts less than z ^ 0.7 (Nichol et al. 1997; Burke et and Appendix B). Table 4 lists the 460 pointings selected to al. 1997; Collins et al. 1997; Vikhlinin et al. 1998b; Rosati et form the Bright SHARC survey. Two points should be al. 1998; Jones et al. 1998; Nichol et al. 1999). At brighter noted about these 460 pointings. First, 371 of the pointings, luminosities, the 160 deg2 and Bright SHARC surveys, have those with three character extensions e.g., ““ n00,ÏÏ ““ a01 ÏÏ provided evidence for negative evolution (Nichol et al. etc., were processed after an important change was made to 1999; Vikhlinin et al. 1998b) similar to that seen in the the Standard Analysis Software System (SASS). This change EMSS cluster sample (Henry et al. 1992; Reichart et al. e†ected those pointings for which the total exposure time 1999). was broken up into more than one observation interval. The SHARC (Serendipitous High-Redshift Archival After the change, each observation interval was analyzed ROSAT Cluster) survey was designed to optimize studies of separately, whereas before the change they were analyzed X-ray cluster evolution and combines two complementary together.