Search for Starbursts among X-Ray--selected Galaxies: Optical Spectroscopy

To establish the nature of X-ray-selected galaxies and to probe the potential contribution of "starburst" galaxies to the X-ray background, we have obtained low-resolution spectra, in the range 3500-7300 A, of the optical counterparts of 15 X-ray sources selected from the Einstein Observatory Extended Medium-Sensitivity Survey and Imaging Proportional Counter Source Catalog. At least three X-ray sources can be classified as starburst galaxies on the basis of line-ratio diagnostics alone. This is consistent with the number expected from recent models which predict that starburst galaxies could account for at least ~15%-20% of the extra- galactic X-ray background at 2 keV.