Rochester Institute of Technology RIT Scholar Works Articles 2007 The CA S Fornax Cluster Survey. I. Introduction to the Survey and Data Reduction Procedures Andrés Jordán European Southern Observatory John P. Blakeslee Washington State University Patrick Côté Herzberg Institute of Astrophysics Laura Ferrarese Herzberg Institute of Astrophysics Leopoldo Infante Pontificia Universidad Católica de Chile See next page for additional authors Follow this and additional works at: http://scholarworks.rit.edu/article Recommended Citation Andrés Jordán et al 2007 ApJS 169 213 This Article is brought to you for free and open access by RIT Scholar Works. It has been accepted for inclusion in Articles by an authorized administrator of RIT Scholar Works. For more information, please contact [email protected]. Authors Andrés Jordán, John P. Blakeslee, Patrick Côté, Laura Ferrarese, Leopoldo Infante, Simona Mei, David Merritt, Eric W. Peng, John L. Tonry, and Michael J. West This article is available at RIT Scholar Works: http://scholarworks.rit.edu/article/1187 Accepted for Publication in ApJS A Preprint typeset using LTEX style emulateapj v. 11/26/04 THE ACS FORNAX CLUSTER SURVEY. I. INTRODUCTION TO THE SURVEY AND DATA REDUCTION PROCEDURES1 Andres´ Jordan´ 2, John P. Blakeslee3, Patrick Cotˆ e´4, Laura Ferrarese4, Leopoldo Infante5, Simona Mei6, David Merritt7, Eric W. Peng4, John L. Tonry8, Michael J. West9,10 Accepted for Publication in ApJS ABSTRACT The Fornax Cluster is a conspicuous cluster of galaxies in the southern hemisphere and the second largest collection of early-type galaxies within <∼ 20 Mpc after the Virgo Cluster. In this paper, we present a brief introduction to the ACS Fornax Cluster Survey — a program to image, in the F475W (g475) and F850LP (z850) bandpasses, 43 early-type galaxies in Fornax using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. Combined with a companion survey of Virgo, the ACS Virgo Cluster Survey, this represents the most comprehensive imaging survey to date of early-type galaxies in cluster environments in terms of depth, spatial resolution, sample size and homogeneity. We describe the selection of the program galaxies, their basic properties, and the main science objectives of the survey which include the measurement of luminosities, colors and structural parameters for globular clusters associated with these galaxies, an analysis of their isophotal properties and surface brightness profiles, and an accurate calibration of the surface brightness fluctuation distance indicator. Finally, we discuss the data reduction procedures adopted for the survey. Subject headings: galaxies: clusters: individual (Fornax) — galaxies: elliptical and lenticular, cD — galaxies: distances and redshifts — galaxies: star clusters — galaxies: nuclei — methods: data analysis 1. INTRODUCTION cluster, the most conspicuous concentration of galaxies in the southern hemisphere, is centered roughly at α ∼ Much of our current understanding of galaxy forma- h m ◦ tion and evolution is based on observations of galaxies 3 35 and δ ∼ −35.7 (Ferguson 1989a). It is located in cluster environments. While not necessarily represen- in the Fornax constellation, which was introduced in the tative of clusters at high redshift, nearby clusters have 18th century by the Abb´eNicolas Louis de la Caille while mapping the southern skies from the Cape of Good Hope played a key role in shaping this understanding for the 11 simple reason that they are amenable to study in a level during the years 1751–1753 . of detail that will never be possible for the more distant To the best of our knowledge, it was first identified as a systems. bonafide galaxy cluster by Shapley (1943) who compiled Among the nearby clusters, Virgo is almost certainly data on many of the most prominent members and wrote the most thoroughly studied. Indeed, it can probably be “Table 3 lists some of the information we have at hand said that Virgo is the most closely examined cluster of concerning a score of bright objects in the constellation galaxies in the entire universe (see, e.g., the discussions Fornax, which are so located with respect to one another in Huchra 1985; Binggeli, Sandage & Tammann 1985; that the law of chance is hard pressed if these objects are only accidentally near together. They appear to con- arXiv:astro-ph/0702320v1 13 Feb 2007 Binggeli 1999; Gavazzi et al. 2003; Cˆot´eet al. 2004). After Virgo, the largest concentration of galaxies within stitute a real colony of galaxies, mutually operating.”. 20 Mpc of our galaxy is the Fornax cluster. This However, a complete census of cluster members was still many years away, and even as late as 1956, NGC 1399 — 1 Based on observations with the NASA/ESA Hubble Space Tele- the luminous cD/E0 galaxy at the dynamical center of scope obtained at the Space Telescope Science Institute, which is the main component of the cluster (Drinkwater, Gregg operated by the Association of Universities for Research in Astron- & Colless 2001a) — was listed as a non-cluster galaxy in omy, Inc., under NASA contract NAS 5-26555 2 European Southern Observatory, Karl-Schwarzschild-Str. 2, the catalog of Humason, Mayall & Sandage (1956). 85748 Garching bei M¨unchen, Germany; [email protected] Studies of the Fornax cluster have often followed on 3 Department of Physics and Astronomy, Washington State Uni- the heels of similar studies of the Virgo cluster. For in- versity, 1245 Webster Hall, Pullman, WA 99163-2814 stance, one of the first studies of Fornax reported the 4 Herzberg Institute of Astrophysics, Victoria, BC V9E 2E7, Canada discovery of dwarf galaxies (Hodge 1959) after a simi- 5 Departamento de Astronom´ıa y Astrof´ısica, Pontificia Univer- lar population had been uncovered in Virgo by Reaves sidad Cat´olica de Chile, Avenida Vicu˜na Mackenna 4860, Casilla (1956). The earliest catalogs of Fornax cluster members 306, Santiago 22, Chile 6 GEPI, Observatoire de Paris, Section de Meudon, 5 place Jules 11 The Fornax constellation was originally named “Le Janssen, 92195 Meudon Cedex, France 7 Fourneau”, later latiniced to “Fornax Chimiae” (Chemical Fur- Department of Physics, Rochester Institute of Technology, 84 nace). In the spirit of the illustration de la Caille named several Lomb Memorial Drive, Rochester, NY 14623 8 constellations after instruments of the liberal and philosophical Institute for Astronomy, University of Hawai’i, 2680 Woodlawn arts. He gave us also ’Apparatus Sculptoris’ (sculptor’s apparatus, Drive, Honolulu, HI 96822 9 now Sculptor) and ’Antlia Pneumatica’ (air pump, now Antlia), Department of Physics & Astronomy, University of Hawai’i, among others. See Evans (1951) for a brief account of La Caille’s Hilo, HI 96720 work in the Cape. 10 Gemini Observatory, Casilla 603, La Serena, Chile 2 JORDAN´ ET AL. (Hodge 1960, Hodge, Pyper & Webb 1965) were eventu- ing capabilities. In the first cycle of operations with ACS, ally supplanted by the Fornax Cluster Catalog (FCC) of we initiated the ACS Virgo Cluster Survey (ACSVCS; Ferguson (1989a), who surveyed 40 square degrees using Cˆot´eet al. 2004), a program to obtain deep F475W (≈ large-scale plates from the 2.5m Las Campanas telescope Sloan g) and F850LP (≈ Sloan z) ACS/WFC images for — the same telescope that was used some years before 100 early-type members of the Virgo cluster. As the sec- to assemble the Virgo Cluster Catalog (Binggeli et al. ond step in a broader program to obtain high-resolution 1985). The FCC remains the most comprehensive cata- imaging for a large, well-defined sample of early-type log of Fornax currently available. galaxies in nearby clusters, we initiated the ACS For- The globular cluster systems of the brightest For- nax Cluster Survey (ACSFCS). This ACS/WFC survey nax galaxies were first tentatively detected around of 43 early-type galaxies in the Fornax cluster was car- NGC 1374, NGC 1379, and NGC 1399 by carrying out ried out using the same observational strategy that was starcounts in a single deep photographic plate (Dawe & employed in the ACSVCS. Collectively, these two sur- Dickens 1975), a full two decades after a similar popula- veys provide homogeneous g475- and z850-band imaging tion had been first discussed for M87, the giant elliptical of 143 galaxies with magnitudes BT <∼ 16, a dataset with in the center of the Virgo cluster (Baum 1955). A system- wide-ranging scientific potential. atic study of globular cluster systems in Fornax was later In this paper, the first in a series, we present an intro- presented by Hanes & Harris (1986) as one of a series of duction to the ACSFCS and discuss the data reduction papers on extragalactic globular clusters (which had in- procedures adopted for it. The paper is organized as cluded the study of globular clusters in Virgo galaxies in follows: we present a brief description of the survey ob- previous installments). jectives in §2, outline selection of sample galaxies in §3 In the all-important task of establishing the cosmo- and describe the observations in §4. We detail the data logical distance ladder, Cepheids were used by the HST reduction procedures of the survey in §5 and conclude Key Project on the Extragalactic Distance Scale to de- in §6. rive a distance to Fornax (Madore et al. 1999) shortly after the same program had identified Cepheids in Virgo 2. MOTIVATION AND OBJECTIVES (Freedman et al. 1994; Ferrarese et al. 1996). Following The motivations for undertaking a high-spatial reso- initial feasibility tests of the surface brightness fluctua- lution, multi-wavelength imaging survey of galaxies in tions (SBF; Tonry & Schneider 1988) distance indicator nearby clusters has been presented in the context of the on M32 and NGC 3379, the method was applied to a sig- ACSVCS by Cˆot´eet al. (2004). The survey images have nificant number of galaxies in the Virgo Cluster (Tonry, a wide-ranging use for a variety of scientific applications, Ajhar & Luppino 1989, 1990).