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Session 14 - Surveys.
Display session, Monday, January 13
As part of a program to investigate the nature of galaxies in low density environments, we present preliminary results from a spectroscopic survey of emission line galaxies in the Bootes Void. The Bootes Void is one of the largest known regions of low density with a radius of 43 Mpc (H_0 = 75 km/sec/Mpc). Twenty six emission line galaxies are known to lie within its boundaries. We have taken spectra of 23 of these galaxies and of one additional void galaxy, 1517+3949, originally discovered in an HI radio survey. The observations were made with the CCD spectrograph on the 1 m telescope at Mount Laguna Observatory. Spectra for the 3 remaining emission line galaxies have been published and will be included in the discussion.
We present preliminary analysis of the spectra in which we use emission line ratio diagnostics to classify the galaxies. Five of the galaxies have [O III] \lambda 5007/H\beta > 3, suggesting that these galaxies may be AGNs. One of these 5 galaxies, I Zw 81, has been previously identified as an AGN. As many as 8 galaxies may have the Mg b (\lambda 5175) absorption feature, indicating the presence of older stellar populations within some of the galaxies. At least 25% of the void galaxies have large H\alpha luminosities compared to the most luminous normal galaxies. Also, for the first time emission lines have been detected in the HI galaxy 1517+3949, bringing the number of emission line galaxies in the Bootes Void to 27.
Mount Laguna Observatory is operated jointly by San Diego State University and the University of Illinois. This research has been supported in part by NASA through the Nevada Space Grant Consortium, and by the Theodore Dunham, Jr. grant from the Fund for Astrophysical Research.
Program listing for Monday