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| Joint Astronomy Centre |
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Tuesday 9 September at 1:30pm @ JACTomotsugu Goto - Univ. of Tokyo
ABSTRACTS: Environmental Effects on Galaxy Evolution and The Origin of E+A Galaxies It is a remarkable feature that various properties of galaxies vary according to their environments. However, only little has been known on the origin of this variety in galaxies. Using the Sloan Digital Sky Survey (SDSS) data, we investigate the morphology-density relation to find two characteristic environment where the morphology-density relation abruptly changes (0.3 and 2 Rvir).The result has significant implication for the underlying physical mechanism since it suggests that two different mechanisms might be responsible for the morphology-density relation. In addition, we study the environment of unusual spiral galaxies with no [OII] or Halpha emission lines (passive spirals), and find that passive spiral galaxies preferentially live in cluster infalling regions (1-10 Rvir}). Thus, the origin of passive spiral galaxies is likely to be cluster related. Based on all of our observational results, we propose possible fate of cluster infalling galaxies. E+A galaxies are interpreted as a post-starburst galaxy due to their strong Balmer absorption lines and their lack of any [OII] or Halpha emission lines. For more than 20 years, however, it has been a mystery why E+A galaxies started starburst and why they stopped star formation abruptly. There have been three possible explanations for E+A galaxies; (i) cluster-related phenomena (e.g., ram-pressure stripping)(ii) galaxy-galaxy merger/interaction (iii) dust enshrouded star formation. Using one of the largest samples of 133 E+A galaxies selected from the Sloan Digital Sky Survey data, we tested these three possible scenarios one by one to reach a definitive conclusion on the origin of E+A galaxies. |