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For refcode 2001AJ....121..793R:
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Copyright by American Astronomical Society. Reproduced by permission
2001AJ....121..793R STARBURSTS VERSUS TRUNCATED STAR FORMATION IN NEARBY CLUSTERS OF GALAXIES JAMES A. ROSE Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599; jim@physics.unc.edu ALEJANDRO E. GABA Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599; gaba@physics.unc.edu NELSON CALDWELL F. L. Whipple Observatory, Smithsonian Institution, P.O. Box 97, Amado, AZ 85645; caldwell@flwo99.sao.arizona.edu AND BRIAN CHABOYER Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755-3528; Brian.Chaboyer@Dartmouth.edu Received 2000 August 11; accepted 2000 November 1 ABSTRACT We present long-slit spectroscopy, B- and R-bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters, which are known to be either in a star-forming phase or to have had star formation that recently terminated. From the long-slit spectra, obtained with the Blanco 4 m telescope, we find that emission lines in the star- forming cluster galaxies are significantly more centrally concentrated than in a sample of field galaxies. The broadband imaging reveals that two currently star-forming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has been concentrated. In contrast, the two galaxies for which star formation has already ended show no central color gradient. The Pegasus I galaxy with the most evident signs of ongoing star formation (NGC 7648), exhibits signatures of a tidal encounter. Neutral hydrogen observations of that galaxy with the Arecibo radio telescope reveal the presence of ~4 x 10^8^ M_sun_ of H I. Arecibo observations of other current or recent star-forming early-type galaxies in Pegasus I indicate smaller amounts of gas in one of them, and only upper limits in others. These observations indicate that NGC 7648 in the Pegasus I cluster owes its present star formation episode to some form of tidal interaction. The same may be true for the other galaxies with centralized star formation, but we cannot rule out the possibility that their outer disks have been removed via ramm pressure stripping, followed by rapid quenching of star formation in the central region. Key words: galaxies: clusters: general-galaxies: elliptical and lenticular, cD-galaxies: evolution-galaxies: interactions -galaxies: starburst- intergalactic medium
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