AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 4. Evolution of Galaxies, Galaxy Surveys
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southwest Exhibit Hall

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[4.04] The Effect of Environment on Galaxy Spectral Type

B.J. Carter, D.G. Fabricant, M.J. Geller, M.J. Kurtz (CfA), B. McLean (STScI)

We have examined the optical spectra of a complete sample of over 3100 galaxies to determine their spectral types as a function of their environment. The sample is drawn from a redshift survey with median z ~.046 which is 90% complete to 15.4 in R\@. All spectra, which cover 3600--7400Å, were taken with a 3 arcsecond slit and have typical S/N ~ 10. We determine spectral types from measurements of detected spectral lines, where H\alpha, [OII]\lambda3727, and other prominent lines are detected at equivalent widths of \ge~5Å\@. Galaxies with detected emission make up slightly more than half our sample. The relative fraction of emission-line galaxies drops at the highest densities, presumably because the cluster environment strips gas from galaxies. The galaxies with the highest star-forming rates (measured from H\alpha flux) occur mainly in the lowest density regions. We also find that both AGNs and galaxies with high star-formation rates are more likely to have nearby companions than less-active galaxies, suggesting that both star formation and AGN activity can be boosted by interactions with a nearby galaxy.

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