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L. Hao, M. A. Strauss (Princeton University), R. R. Rojas, M. S. Vogeley (Drexel University), Sloan Digital Sky Survey Collaboration
From the Sloan Digital Sky Survey (SDSS) spectroscopic data, we have obtained an emission line galaxy sample of 18,461 galaxies in approximately 1986 deg2. We measure their oxygen abundances via three different methods. 430 galaxies have prominent [OIII]\lambda 4364 lines, allowing their temperatures and oxygen abundances to be measured directly. For the rest of the galaxies, an indirect method of using strong emission lines is adopted. In particular, we apply the oxygen abundance techniques developed by McGaugh (1991) and Pilyugin (2000) respectively. The resulting oxygen abundances measured by the three methods are compared. We find that there is a large amount of scatter among the different calibrations. Despite these uncertainties, we use the abundance measured via the McGaugh model to build the connection between metallicity of galaxies and their environment, which is characterized by the distance to their nth nearest neighbor. We find that there is a clear deficiency of metal-poor galaxies in very dense environments. In moderately dense environments, metal-poor galaxies are systematically more isolated than are metal-rich galaxies, which are yet more isolated than pure absorption-line galaxies. However for very isolated galaxies, such as those defined as void galaxies (Rojas et al. 2003), the normalized fraction of metal-poor and metal-rich galaxies are about the same, both exceeding the fraction of pure absorption line galaxies. The deficiency of metal-poor galaxies in dense environments is in agreement with the biased galaxy formation model (Dekel & Silk 1986), in which the majority of dwarf galaxies originate as low-mass primordial density fluctuations.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.