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T. Goto (Johns Hopkins University), SDSS Collaboration
E+A galaxies are characterized as a galaxy with strong Balmer absorption lines but without any [OII] or H\alpha emission lines. The existence of strong Balmer absorption lines means that E+A galaxies have experienced starburst within recent one Gyr. However, the lack of [OII] nor H\alpha emission lines indicates that E+A galaxies do not have any on-going star formation. Therefore, E+A galaxies are interpreted as a post-starburst galaxy. In this work, we pursue the origin of E+A galaxies using one of the largest samples of 133 E+A galaxies selected from the Sloan Digital Sky Survey data. We tested three popular explanations for E+A galaxies; (i) cluster-related phenomena (e.g., ram-pressure stripping) (ii) galaxy-galaxy merger/interaction (iii) dust enshrouded star formation. By studying the environment of E+A galaxies as a function of local galaxy density, we found many E+A galaxies in the rarefied field region. These field E+A galaxies can not be explained by the cluster related phenomena. The optical-infrared colors of E+A galaxies are not much redder than normal galaxies. Radio derived star formation rate shows that E+As are not dusty starbursting galaxies. Therefore, dusty star formation origin is not plausible. Based on the population synthesis model, we identified young E+A galaxies as a galaxy 270-430 Myrs after the burst (E+As with H\delta EW > 7Å). While examining the image of these galaxies, we found that the young E+As often have accompanying galaxies. Statistically, these galaxies have, in fact, accompanying galaxies ~2.5 (8.0) times more frequent than randomly selected galaxies within 75 (50) kpc at two \sigma significance level. Considering that neither the dusty origin nor the cluster origin is plausible, we conclude that merger/interaction with closely accompanying galaxies is the most likely mechanism to be responsible for the E+A phenomenon.
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The author(s) of this abstract have provided an email address for comments about the abstract: tomo@jhu.edu
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.