The Role of Environment in Galaxy Evolution: Results From a Multi--Wavelength Survey of Loose Groups

Previous abstract Next abstract

Session 114 -- Compact Groups, Galaxy and Quasar Clustering
Oral presentation, Thursday, 12, 1995, 10:00am - 11:30am

[114.01D] The Role of Environment in Galaxy Evolution: Results From a Multi--Wavelength Survey of Loose Groups

P.M.Marcum (U. Va), J.S.Gallagher (U. Wisconsin), P.N.Appleton (ISU)

The relationship between galaxy evolution and environment is not well understood. Indeed, the very existance of a direct relationship in the low density non--cluster environments is still debatable. To address this issue, we have produced an infrared (JHK) and optical (R--band and $H\alpha$) imaging survey of loose groups from the CfA catalogue (Geller \& Huchra 1983). Specifically, we use this data set to assess the role of the local environment and global group traits in shaping basic galaxy properties such as star formation rates (SFR), presence/absence of bars, R--band luminosity functions, near infrared colors, and morphological types.

The physical nature of the loose groups themselves and where they fit into the hierarchy of other multi-galaxy systems (e.g., clusters or compact groups of galaxies) is a matter of debate. However, the postulate that compact groups are transient ``condensations'' which are created during the infall of loose groups has recently received support through computational simulations. One observational consequence could be loose groups having a large fraction of their members with signatures of past strong tidal interactions and/or mergers. Thus, a third goal is to look for ``evolved'' groups containing many galaxies showing peculiar morphologies, enhanced SFR's, or having unusual luminosity functions.

My project compared characteristics of: (1) groups of galaxies having at least one member listed in the Catalogue of Pecular Galaxies (Arp 1966); and (2) ``control'' groups containing ``normal'', relatively isolated galaxies. The more interesting findings include: (i) all the galaxies have similar near infrared colors which lie inexplicably close to those of the dwarf stellar track. (ii) While the Arp galaxies do show a great enhancement in SFR's and the occurence of bars, the galaxies which are neighbors to the Arp galaxies have properties which are as ``normal'' as those of the control groups, suggesting that most of the galaxies in the groups containing peculiar galaxies have not experienced strong interactions in their past.

Thursday program listing