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For refcode 1994ApJ...437L.103M:
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Copyright by American Astronomical Society. Reproduced by permission
1994ApJ...437L.103M LENSING BY COMPACT GROUPS OF GALAXIES C. MENDES DE OLIVEIRA European Southern Observatory, La Silla, Casilla 19001, Santiago. Chile; coliveir@eso.org AND E. GIRAUD European Southern Observatory, La Silla, Casilla 19001, Santiago, Chile; and Observatoire de Marseille, Place Le Verrier, 13248 Marseille Cedex 4, France; egiraud@eso.org Received 1994 July 14; accepted 1994 September 30 ABSTRACT The observations of diffuse X-ray emission attributed to a hot intragroup gas observed in some of the Hickson compact groups of galaxies suggest that a fraction of these objects are physical entities embedded in large potential wells. We analyze here the average efficiency of compact groups as gravitational lenses. Assuming the conservative hypothesis of an isothermal profile for the mass distribution of the group, and using the measured dynamical parameters of each Hickson compact group, we find that very few of the groups are able to image objects onto arcs. However, a high fraction of groups have densities close to the critical density, and they can distort and enhance the magnitudes of background galaxies. A fraction of 5%-66%, depending on the core radius assumed for the density profile of the group, can cause amplifications of at least 0.5 mag on background galaxies situated at twice the distance of the group. Our most interesting result, however, is that, more than one-third of a hypothetical distant sample of compact groups, with intrinsic parameters similar to Hickson's, could image background galaxies onto arcs, if they were at distances an order of magnitude higher (z ~ 0.2). At these redshifts, more than two-thirds of the groups can amplify background objects by >= 0.5 mag. Subject headings: galaxies: clustering - gravitational lensing
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