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Date and Time of the Query: 2019-06-18 T21:05:40 PDT
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For refcode 1989A&A...222....5P:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1989A&A...222....5P Hierarchical pairs and the evolution of elliptical galaxies P. Prugniel, E. Davoust, and J.-L. Nieto Observatoire Midi-Pyrenees, Laboratoire Associe au CNRS n 285, 14, Avenue E Belin, F-31400 Toulouse, France Received October 3, 1988; accepted February 28, 1989 Summary. We investigate the photometric and kinematic characteristics of galaxies in 8 close pairs of ellipticals involving a bright galaxy and a faint companion of compact aspect. The photometric and geometric characteristics of the individual galaxies are determined after an automatic iterative procedure disentangles the light contribution from each galaxy of the pairs. Redshifts and central velocity dispersions are also determined, from high-dispersion spectra. The fainter galaxies of our pairs have photometric and kinematic characteristics intermediate between those of massive and compact (M32-type) ellipticals. Evidence for interaction in these pairs includes strong isophote twists in most galaxies and isophote off-centerings in two pairs, but no truncation of the photometric profiles. Despite the interaction, our galaxies belong to the "fundamental plane" of ellipticals. This is evidence for the robustness of this plane against gravitational encounters. Furthermore, their mean surface brightness and their central velocity dispersion are tightly correlated with their luminosity. This is particularly true for the fainter galaxies which are among the ellipticals of higher surface brightness and velocity dispersion at a given luminosity. This leads us to define two sequences of ellipticals (excluding dwarf spheroidals) on the basis of their kinematic and photometric characteristics, extending earlier work by Michard. Our galaxies, as well as classical compact ellipticals and most of the luminous ellipticals, appear to belong to the first sequence. The galaxies of the second sequence are characterized by a lower surface brightness and a lower velocity dispersion than sequence I galaxies. Gravitational interaction provides a physical basis for this dichotomy. Our pairs belong to sequence I, composed of systems whose properties result from their presence in a dense environment. The galaxies of sequence II evolve toward sequence I through dissipation of internal energy and loss of angular momentum, driven by the tidal interaction. This scenario is suggested to be a general and important factor in the dynamical evolution of elliptical galaxies. Key words: galaxies: ellipticals, compact - galaxies: structure, kinematics and dynamics - evolution
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