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University of Groningen the Galaxy Population in the Coma Cluster Beijersbergen, Marco University of Groningen The galaxy population in the Coma cluster Beijersbergen, Marco IMPORTANT NOTE: You are advised to consult the publisher's version (publisher's PDF) if you wish to cite from it. Please check the document version below. Document Version Publisher's PDF, also known as Version of record Publication date: 2003 Link to publication in University of Groningen/UMCG research database Citation for published version (APA): Beijersbergen, M. (2003). The galaxy population in the Coma cluster. s.n. Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons). The publication may also be distributed here under the terms of Article 25fa of the Dutch Copyright Act, indicated by the “Taverne” license. More information can be found on the University of Groningen website: https://www.rug.nl/library/open-access/self-archiving-pure/taverne- amendment. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Download date: 07-10-2021 4 A Catalogue of Galaxies in the Coma Cluster Morphologies, Luminosity Functions and Cluster Dynamics M. Beijersbergen & J. M. van der Hulst ABSTRACT — We present a new multi-color catalogue of 583 spectroscopically confirmed members of the Coma cluster based on a deep wide field survey covering 5.2 deg2. This large, uniform data set provides an excellent low redshift comparison sample for studies of galaxies in distant clusters. We use it to study the galaxy luminosity function (LF) and its dependence on distance to the cluster center. Comparison to LFs derived without spectroscopic membership information shows good agreement between both determinations of the LFs. The spatial and velocity distributions of different galaxy types are examined. It is found that the early-type galaxies have a Gaussian velocity distribution, whereas the late-types have not. We find cz = 6926, σ = 893 km s−1 for early-type galaxies and cz = 7243, σ = 1077 km s−1 for late-types. This result is consistent with the hypothesis that early-type galaxies are a virialized cluster population and part of the late-types are still falling onto the cluster. In the cluster center the galaxy composition is markedly different than in the cluster outer parts. The relative fractions of early- and late-type galaxies in the cluster center are 90% and 10%, respectively, versus 60% and 40% at all measured radii outside∼of the cluster∼core. ∼ ∼ CHAPTER 4. A CATALOGUE OF GALAXIES IN THE COMA CLUSTER 50 4.1 Introduction The Coma cluster (Abell 1656, z = 0.023) is the best studied rich cluster of galaxies in the nearby universe. The amount of evidence for significant substructures has largely grown, in particular through X-ray studies (e.g. White et al. 1993; Briel et al. 2001; Arnaud et al. 2001) and the once generally accepted view of Coma being a relaxed, virialized cluster must be abandoned. The presence of two dominant central galaxies (NGC 4874 and NGC 4889), with velocities significantly different from the cluster mean, indicates that the cluster is not completely virialized. A third dominant galaxy (NGC 4839) is located 400 south-west of the cluster center and is either about to merge with the main cluster (e.g. Colless & Dunn 1996) or has already made one pass through (e.g. Bravo-Alfaro et al. 2000). The Coma cluster has a high galactic latitude (b = 88◦) and a low redshift which makes it best suited as z = 0 reference for studies of galaxy formation and evolution. But despite the large amounts of data and numerous studies that focused on the Coma cluster there remains controversy on many aspects of its galaxy population. It is therefore essential to have accurate CCD based and uniform morphological classifications for as many members as possible (Fabricant et al. 2000). Studies of the galaxy population in Coma have hitherto been based on morphological classifications from either photographic plates (e.g. Dressler 1980) or from CCD observations of relatively small samples (e.g. Andreon et al. 1996). We have obtained the largest uniform multi-color catalogue of classified galaxies in the Coma cluster based on high resolution CCD observations. The high data quality makes it perfectly suited to re-study properties of Coma’s galaxy population based on an unprecedented sample of cluster members. Published work on galaxy luminosity functions (LF) in Coma has been based on a statisti- cal method (e.g. Lobo et al. 1997; Bernstein et al. 1995) or on samples of redshift confirmed members (e.g. Biviano et al. 1995; Adami et al. 2000). Our data set offers the possibility to directly compare the results from both methods for galaxies drawn from the same parent distribution. Recent work by Adami et al. (2000) suggests that the number of faint galaxies belonging to Coma estimated from spectroscopic data could be much smaller than estimated by using a statistical field subtraction. Their result, however, is based on a very small region located near the cluster center and we can now test this idea for much larger areas of Coma. Until now relatively few attempts have been made to determine how LFs vary for different galaxy types. Small samples of confirmed members are the main reason to compose so-called composite clusters in order to obtain sufficiently high numbers of galaxies to determine the LF for each galaxy type. Andreon (1998) presented improved type-dependent LFs (LFT) based on a cluster composed of three poor and two rich clusters that supersede previous determi- nations for such a large range of environments. The bright parts of the LFTs of galaxies in Coma can be compared to his results to test their proposed universality (Binggeli et al. 1988; Andreon 1998). Colless & Dunn (1996) were the first to detect statistically significant substructure in the galaxy line-of-sight velocity distribution. Based on the galaxy’s position in the color- magnitude diagram they identified early- and late-type galaxies and studied their kinematics. Their results support the hypothesis that the early-type galaxies are a virialized cluster popula- tion and the late-type galaxies a freely infalling population. The new Coma catalogue allows a much more accurate study of the kinematics of the different galaxy populations in Coma. The morphological segregation in clusters was first demonstrated by Dressler (1980) and 51 COMA CATALOGUE Figure 4.1— Low resolution, 10 10 binned, mosaic image with annuli× overlaid. Radii are: I: 0-0.2, II: 0.2- 0.3, III: 0.3-0.42, IV: 0.42-0.74 and ◦ −1 V: 0.74-1.4 degrees (1 = 1:22 h100 Mpc at Coma distance). All spec- troscopically confirmed cluster mem- bers are enclosed in circles. The ob- served area spans 5:2 deg2. North is up and east is to∼the left. seems to be a well established fact by now (Dressler et al. 1997; Whitmore et al. 1993). Most studies searched for segregation with respect to density or radius by averaging data of many clusters in order to obtain sufficiently large samples of each galaxy type. But in Coma, surprisingly, Andreon (1996) failed to find any morphological segregation within 1 degree from the cluster center. The new Coma data provides a more complete sample and allows to study the morphological composition out to larger cluster radii. We have used the Wide Field Camera (WFC) on the Isaac Newton Telescope (INT) to obtain a large and uniform multi-color catalogue of the Coma cluster area. We identify 583 members and 219 non-members in our survey and extend the number of galaxies with reliable morphological classifications down to fainter limits. Our catalogue provides an accurate low z zeropoint for studies of the evolution of galaxy morphology, color and luminosity. In this chapter, we use it to study the shapes of the general LFs. The LFs derived from the cluster members can be directly compared to statistical results (Beijersbergen et al. 2002) and give good estimates of the accuracy of the statistical method. In addition, we extend the work by Adami et al. (2000) over a much larger area. Van Dokkum classified as many galaxies as possible in our survey (for details see van Dokkum et al. 2002) and here we use these classifications to construct type-dependent LFs and to examine the spatial and kinematical distributions of the different galaxy types. −1 Throughout this chapter we use H0 = 100 h100 km s and a distance modulus of 34.23. 4.2 Coma catalogue 4.2.1 Observations We have undertaken a large photometric survey of the Coma cluster with the WFC on the INT. The total area covered by the observations is 5:2 deg2 in the B and r bands and 1:3 deg2 in the U band. A complete description of the∼observations and the pipeline data reduction∼ is given in Beijersbergen et al. (2002). In short, we have used 25 overlapping WFC pointings with broadband filters RGO U, Harris B and Sloan r to create a uniform multi-color catalogue CHAPTER 4. A CATALOGUE OF GALAXIES IN THE COMA CLUSTER 52 Figure 4.2— Slice diagram display- ing the spatial and velocity distribu- tions of all identified Coma mem- bers.
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