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Date and Time of the Query: 2019-04-25 T00:51:25 PDT
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For refcode 2003A&A...399..813F:
Retrieve 192 NED objects in this reference.
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NED Abstract

Copyright by European Southern Observatory (ESO). Reproduced by permission
2003A&A...399..813F Multiple merging events in Abell 521 C. Ferrari, S. Maurogordato, A. Cappi, C. Benoist 1 - CERGA, UMR 6527, CNRS, Observatoire de la Cote d'Azur, BP 4229, Le Mont-Gros, 06304 Nice Cedex 4, France 2 - INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy Received 12 August 2002 / Accepted 12 November 2002 Abstract. We present a detailed spatial and dynamical analysis of the central ~2.2 h_75_^-1^ Mpc region of the galaxy cluster Abell 521 (z= 0.247), based on 238 spectra (of which 191 new measurements) obtained at the 3.6 m Telescope of the European Southern Observatory and at the Canada-France-Hawaii Telescope. From the analysis of the 125 galaxies that are confirmed members of the cluster, we derive a location ("mean" velocity) of C_BI_ = 74 019^+112^ _-125_ km s^-1^ and detect a complex velocity distribution with high velocity scale ("dispersion", S_BI_ = 1325^+145^ _-100_ km s^-1^), but clear departure from a single Gaussian component. When excluding a possible background group of four galaxies, the velocity dispersion remains still large (~1200 km s^-1^). The general structure of the cluster follows a North-West/South-East direction, crossed by a perpendicular high density "ridge" of galaxies in the core region. The Northern region of the cluster is characterized by a lower velocity dispersion as compared to the whole cluster value; it hosts the BCG and a dynamically bound complex of galaxies, and it is associated with a group detected in X-ray (Arnaud et al. #!Arn00!#). This region could be in a stage of pre-merger onto the main cluster. The small offset (~+250 km s^-1^) in the mean velocity of the northern region as compared to the whole cluster suggests that the merging occurs partly in the plane of the sky. These results, taken together with the fact that most of the clumps detected on the isodensity maps, as well as the early-type galaxies and the brightest ones (L<L^*^) are aligned, suggest that this North-West/South-East direction is the preferred one for the formation of this cluster. The central high dense region ("ridge") shows a lower velocity location ( C_BI_ = 73 625^+344^ _-350_ km s^-1^) and significantly higher scale ( 1780^+234^ _-142_ km s^-1^) as compared to the whole cluster values. This is due to the presence of a low-velocity group of galaxies with a high fraction of emission line objects. This can be explained in a scenario in which a merging of subclusters has recently occurred along the direction of the "ridge" with a significant component along the line of sight. The low-velocity group would then be a high-speed remnant of the collision which would have also triggered an episode of intense star formation responsible for the large fraction of late-type objects in this region. Key words: galaxies: clusters: general - galaxies: clusters: individual: Abell 521 - galaxies: distances and redshifts - cosmology: observations
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