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For refcode 1989AJ.....98.2044V:
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1989AJ.....98.2044V THE BUTCHER-OEMLER EFFECT IN A NEARBY CLUSTER OF GALAXIES? LAURENT VIGROUX AND OLIVIER BOULADE Service d-Astrophysique, CEN-Saclay, 91191 Gif-sur-Yvette, France JAMES A. ROSE Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599 Received 27 June 1989 ABSTRACT A comparative study has been made between the integrated spectra of early-type galaxies in the nearby Abell 262, Pegasus I, and Virgo Clusters of galaxies, and those of a number of "field" galaxies. Both A262 and Pegasus I are comparable in richness to the Virgo Cluster, but while A262 has a similar x-ray luminosity to that of Virgo, that of Pegasus I is at least an order of magnitude lower. Spectra have been obtained for ten galaxies in each cluster using the UV prime focus spectrograph at the Canada-France-Hawaii Telescope; the spectra cover the wavelength region 3500-4300 A at a resolution of 2.5 A (FWHM). The following results have been obtained: (I) In Pegasus I, spectra for five of the ten early-type galaxies studied show evidence of recent star formation, similar to the "starburst" and "post starburst" spectra found by Gunn and Dressler (1988) for blue galaxies in Butcher-Oemler (1984) clusters. This large fraction of early-type galaxies undergoing recent star formation is well in excess of that found in nearby "field" galaxies and in the Virgo Cluster. In A262, one galaxy (out of ten studied) exhibits similar evidence for recent star formation. (2) The star-forming galaxies may be preferentially located outside of the central regions of the two clusters. In Pegasus I, three of the five star-forming galaxies are at radial distances greater than 0.75 Mpc from the cluster center (for H_0_ = 75 km s^-1^ Mpc^-1^). In A262, the sole star-forming galaxy is also situated at R > 0.75 Mpc. (3) The average absolute blue magnitude for the star-forming galaxies is M_B_ ~ -20. Their B - V colors are ~0.15 mag bluer than for the normal galaxies. (4) Both the five star-forming and the five normal early-type galaxies in Pegasus I are unexceptional in terms of their H I content in that upper limits on their H I mass is typically (2-3) x 10^9^ M_sun_ (Richter and Huchtmeier (1982). Given that an unusually large fraction of early-type galaxies in Pegasus I exhibits similar star-formation activity to that of the "starburst" and "poststarburst" galaxies in Butcher-Oemler (B-O) clusters at z > 0.2, and that the star-forming galaxies appear to be located outside the cluster center, as in the case of those in B-O clusters, we may be observing a low-redshift analog to the B-O effect. If so, the fact that the Pegasus I cluster has a very low x-ray luminosity, internal velocity dispersion, and richness compared to the typical B-O cluster indicates that low-redshift counterparts to the B-O effect should be sought primarily in clusters that are at early stages of their dynamical evolution.
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