AN OPTICAL STUDY OF THE NUCLEI OF S0 STAR-BURST GALAXIES

Abstract

Optical observations of the nuclei of 10 S0 Markarian galaxies and two non-Markarian early type galaxies have been obtained with the McDonald Observatory 2.7m telescope. The spectra of 7 Markarian galaxies show deep Balmer absorption lines and stellar-like continua. The nuclear spectra of UGC 01157, 04902, 06570, and 12618 show strong (O II), (O III), and H$\beta$ emission lines analogous to normal H II regions. None of the galaxy continua show a featureless non-thermal component or (O I) $\lambda$ 6300 line emission typical of LINER activity. The continua of UGC 02093 and 07933 are similar to normal early type galaxies. Composite model spectra with decreasing birthrates, IMF exponents of $-1$, $-2.5$, and $-4$, and solar metallicity have been constructed from observed stellar spectra. Comparison of CaH + H$\varepsilon$ to CaK absorption line flux ratios measured in 5 star-burst galaxies to single star-bust episode models implies stellar population ages greater than 5 $\times$ 10\sp9 years