Test of Current Ideas about Compact Groups of Galaxies

Details Test of Current Ideas about Compact Groups of Galaxies Test of Current Ideas about Compact Groups of Galaxies

Dec 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........2r&link_type=abstract

Thesis (PHD). THE UNIVERSITY OF ALABAMA , Source DAI-B 58/06, p. 3091, Dec 1997, 152 pages.

Physics

2

Vv 172, Seyfert'S Sextet

Scientific paper

In this dissertation we test a number of current ideas about compact groups by focusing on some fundamental paradoxes that they pose about galaxy evolution. Conflicts between observations and models have led some to propose that compact groups are not real physical systems. We tested the physical reality of the groups by studying the strength of the interaction-induced enhancement in the optical and infrared luminosity functions. We also searched for optical interaction tracers in two famous groups: VV 172 and Seyfert's Sextet. The presence of a luminosity enhancement was verified, relative to a sample of isolated field galaxies, supporting the reality of, at least, some of the groups. The luminosity function enhancement was found to be smaller than the one observed in samples of paired galaxies and, especially, merger candidates. We also addressed the question of which groups were most likely physical with a statistical analysis of their environment relative to field galaxies, loose groups, and clusters of galaxies. Groups of only three accordant members were found to be more likely chance alignments and to be located closer to denser aggregates of galaxies than field galaxies. Models for compact groups predict that they are dynamically unstable to rapid coalescence. We searched for the (theoretically) expected population of merger remnants by comparing the optical luminosity function of the groups as units with that of field ellipticals. We found very few field ellipticals with luminosities as high as those expected from compact group mergers even allowing for some dimming. The detection of optical diffuse light in the potential of VV 172 is a further indication that these systems are physically dense and more dynamically evolved than predicted by the theoretical models. A detailed analysis of Seyfert's Sextet using Hubble Space Telescope images revealed that a quiescent coalescence event may be occurring among the galaxies in that compact group. Compact groups also show a surprising number of discordant redshift components. We tested the relative distance between the discordant redshift member and the accordant quartet of galaxies in Seyfert's Sextet. The result is consistent with the chance alignment hypothesis.

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