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For refcode 1999ApJ...518...94I:
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1999ApJ...518...94I On the Influence of the Environment on the Star Formation Rates of a Sample of Galaxies in Nearby Compact Groups J. IGLESIAS-PARAMO AND J. M. VILCHEZ Instituto de Astrofisica de Canarias, C/Via Lactea s.n., 38200 La Laguna, Tenerife, Spain; jiglesia@ll.iac.es, jvm@ll.iac.es Received 1998 September 18; accepted 1999 January 19 ABSTRACT We present the results of a study of the star formation rates (SFRs) of a sample of disk galaxies in nearby compact groups compared with the SFRs of a sample of field galaxies. For this purpose, H{alpha} luminosities and equivalent widths were derived for the galaxies of our sample. A direct comparison of the equivalent widths and H{alpha} luminosities, normalized to the B luminosities and estimated area of the galaxies of both samples, yields the result that the median values of these quantities are almost identical for both samples, although the distributions for the compact- group sample are broader around the mean value than was found in the field galaxy sample. This result can be explained by assuming that although interactions between galaxies in compact groups can alter the SFRs, the median value of the normalized SFRs is preserved, being almost indistinguishable from the corresponding value for field galaxies. Measuring the global L_H{alpha}_/L_B_ of the groups, including early-type galaxies, we find that most of the groups that show the highest level of L_H{alpha}_/L_B_ with respect to a set of synthetic groups built out of field galaxies show tidal features in at least one of their members. Finally, we have explored the relationship between the ratio L_H{alpha}_/L_B_ and several relevant dynamical parameters of the groups: velocity dispersion, crossing time, radius, and the mass-to-luminosity ratio, finding no clear correlation. This suggests that the exact dynamical state of a group does not control the SFR of the group as a whole. Our results are compatible with a scenario for compact groups of galaxies in which the dark matter of the group is arranged in a common halo, therefore preventing a fast collapse of the galaxies. Subject headings: galaxies: clusters: general-galaxies: interactions- galaxies: ISM-galaxies: stellar content
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