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S.D. Hunsberger (Lowell), A.D. Glenn (U. Wisc.), J.C. Charlton, R. Ciardullo (Penn State), D. Zaritsky (UCSC)
Compact groups are active sites of galaxy interactions/mergers and thus provide an environment in which to study the formation of dwarf galaxies in tidal debris, i.e., tidal dwarfs. Such dwarf galaxies, still within the tidal debris where they were born, are being studied in both field and cluster environments (Duc and Mirabel 1997, Hibbard et al. 1997, Malphrus et al. 1997). In order to evaluate their contribution to the general galaxy population, we need to focus on some property which distinguishes ``tidal'' dwarfs from ``classical'' dwarfs (those galaxies whose origin is primordial).
If tidal dwarf galaxies are formed from material stripped from the outer regions of giant galaxies then we expect enhanced metallicities in dwarfs of tidal origin, particularly those produced during the present epoch when the ISM of giant galaxies has been chemically enriched by many generations of stars. Duc and Mirabel (1998) report that their sample of tidal dwarf galaxies are more metal rich than classical dwarfs of the same luminosity.
In a survey of 42 Hickson compact groups (HCGs), we detected 47 tidal dwarf candidates (Hunsberger et al. 1996). In two of the groups (HCGs 31 and 92), 15 candidates were also emission-line objects. We obtained long-slit spectra with the Kitt Peak 2.1m and used the line ratio [OII]+[OIII]/[H\beta] to estimate oxygen abundances. We find higher than expected oxygen abundances based on the metallicity-luminosity relation for ``classical'' dwarfs (Richer and McCall 1995, Skillman et al. 1989). We will present our results and discuss implications for assessing the survivability of tidal dwarfs in compact groups and other environments.
The author(s) of this abstract have provided an email address for comments about the abstract: sdh@lowell.edu