EDP Sciences
Free access
Volume 408, Number 3, September IV 2003
Page(s) 905 - 913
Section Galactic structure and dynamics
DOI http://dx.doi.org/10.1051/0004-6361:20031016

A&A 408, 905-913 (2003)
DOI: 10.1051/0004-6361:20031016

Nature and environment of Very Luminous Galaxies

A. Cappi1, C. Benoist2, L. N. da Costa3 and S. Maurogordato4

1  INAF, Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
2  CERGA, Observatoire de la Côte d'Azur, BP 4229, Le Mont-Gros, 06304 Nice Cedex 4, France
    e-mail: benoist@obs-nice.fr
3  European Southern Observatory, Karl Schwartzschildsrtra $\beta$e 2, 85748 Garching bei München, Germany
    e-mail: ldacosta@eso.org
4  CERGA, CNRS, Observatoire de la Côte d'Azur, BP 4229, Le Mont-Gros, 06304 Nice Cedex 4, France
    e-mail: maurogor@obs-nice.fr

(Received 21 February 2003 / Accepted 12 June 2003)

The most luminous galaxies in the blue passband have a larger correlation amplitude than L* galaxies. They do not appear to be preferentially located in rich clusters or groups, but a significant fraction of them seem to be in systems which include fainter members. We present an analysis of fields centered on 18 Very Luminous Galaxies ( $M_B \le -21$) selected from the Southern Sky Redshift Survey 2, based on new observations and public data of the 2dF Galaxy Redshift Survey; we present also additional data on a CfA VLG and on Arp 127. We find that all the selected VLGs are physically associated with fainter companions. Moreover, there is a relation between the VLG morphology (early or late) and the dynamical properties of the system, which reflects the morphology-density relation. 6 out of the 18 SSRS2 VLGs are early type galaxies: 2 are in the center of rich Abell clusters with velocity dispersion $\sigma \sim 600$ km s -1, and the other 4 are in poor clusters or groups with $\sigma \sim 300$. The VLG extracted from the CfA catalog is also an elliptical in a Zwicky cluster. The remaining 2/3 of the sample are late-type VLGs, generally found in poorer systems with a larger spread in velocity dispersion, from ~100 up to ~750 km s -1. The low velocity dispersion, late-type VLG dominated systems appear to be analogous to our own Local Group. The possibile association of VLG systems with dark matter halos with mass comparable to rich groups or clusters, as suggested by the comparable correlation amplitude, would imply significant differences in the galaxy formation process. This work also shows that observing fields around VLGs represents an effective way of identifying galaxy systems which are not selected through other traditional techniques.

Key words: cosmology: observations -- galaxies: distances and redshifts -- galaxies: kinematics and dynamics

Offprint request: A. Cappi, cappi@bo.astro.it

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