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Morphologies and stellar populations of galaxies in the core of Abell 2218

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Sánchez, S. F. and Cardiel López, Nicolás and Verheijen, M. A. W. and Pedraz, S. and Covone, G. (2007) Morphologies and stellar populations of galaxies in the core of Abell 2218. Monthly notices of the Royal Astronomical Society, 376 (1). pp. 125-150. ISSN 0035-8711

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Official URL: http://dx.doi.org/10.1111/j.1365-2966.2007.11335.x




Abstract

We present a study of the stellar populations and morphologies of galaxies in the core of the galaxy cluster Abell 2218. Integral field spectroscopy (IFS) observations were performed using PMAS in the PPAK mode covering a field of view of similar to 74 x 64 arcsec(2) centred on the core of the cluster, in order to obtain spectroscopy of an unbiased flux-limited sample of cluster galaxies. 43 objects were detected in the IFS data, 31 of them with enough signal-to-noise ratio to derive the redshift, all of them brighter than I < 21.5 mag. 28 are at the redshift of the cluster (17 with previously unknown redshift). Individual spectra of the cluster members were extracted and compared with single stellar population models to derive the luminosity-weighted ages and metallicities. In addition, deep Hubble Space Telescope (HST)/ACS F475W-, F555W-, F625W- and F850LP-band images centred on the cluster core were obtained from the HST archive (z(lim) similar to 28 mag). A detailed morphological analysis of all the galaxies within the field of view of these images down to z(lim) < 22.5 mag was performed classifying them as late-type, intermediate and early-type, on the basis of their Sersic indices. The literature was scanned to look for spectroscopically confirmed cluster members located within the field of view of the ACS image. The final sample of 59 galaxies comprises our reported sample of 28 galaxies in the core, and 31 additional galaxies in the outer regions. In addition, multiband broad-band photometry was extracted from the literature for all objects. The morphologically segregated colour-magnitude diagram shows that the early-type galaxies cover the range of brighter and redder colours (the so-called 'red sequence'). A large fraction of spiral galaxies (similar to 50 per cent) is found, most of them fainter than the limit of previous studies. They cover a wide range in colours, from blue colours typical of Butcher-Oemler galaxies to red colours similar to those of early-type galaxies. This result indicates that early-type galaxies are more massive and have older stellar populations, while late-type galaxies are less massive and have a wider range of stellar populations. The distribution of luminosity-weighted ages as a function of metallicities and luminosity-weighted masses, and the distribution of Sersic indices as a function of the luminosity-weighted masses confirm these results. They in fact agree with a proposed two-step scenario for the evolution of galaxies in clusters, where the star formation is quenched first in the infalling spirals, after which a morphological transformation follows that requires larger time-scales. This scenario naturally explains the population faint late-type galaxies with old stellar populations observed in this cluster. In addition, an extremely blue merging galaxy system is found at the core, with the nominal redshift of the cluster.


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This article has been accepted for publication in Monthly notices of the Royal Astronomical Society. © 2007 The Authors. Journal compilation. © 2007 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). Based in part on observations with the NASA/ESA HST, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. We thank Dr R. Gredel, former director of Calar Alto, for supporting this work and providing us with the telescope time for finishing it. We thank support from the Spanish Plan Nacional de Astronomía programme AYA2005-09413-C02-02, of the Spanish Ministery of Education and Science and the Plan Andaluz de Investigación of Junta de Andalucía as research group FQM322. We thank Dr R. Peletier, who kindly read the article cleaning the English. His comments on the science content have helped us to increase the quality of this article.

Uncontrolled Keywords:Integral-field spectroscopy; Potsdam multiaperture spectrophotometer; Dynamically hot galaxies; Extra-galactic nebulae; Distant rich clusters; To-light ratios; Star-formation; Elliptic galaxies; Surface photometry; Globular-clusters
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
Sciences > Physics > Atmospheric physics
ID Code:28287
Deposited On:11 Feb 2015 15:54
Last Modified:10 Dec 2018 15:05

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