Distributions of Galaxy Spectral Types in the Sloan Digital Sky Survey

We perform an objective classification of 170,000 galaxy spectra in the SloanDigital Sky Survey (SDSS) using the Karhunen-Lo\`eve (KL) transform. With aboutone-sixth of the total set of galaxy spectra which will be obtained by thesurvey, we are able to carry out the most extensive analysis of its kind todate. The formalism proposed by Connolly and Szalay is adopted to correct forgappy regions in the spectra, and to derive eigenspectra and eigencoefficients. From this analysis, we show that this gap-correction formalism leads to aconverging set of eigenspectra and KL-repaired spectra. Furthermore, KLeigenspectra of galaxies are found to be convergent not only as a function ofiteration, but also as a function of the number of randomly selected galaxyspectra used in the analysis. From these data a set of ten eigenspectra ofgalaxy spectra are constructed, with rest-wavelength coverage 3450-8350angstrom. The eigencoefficients describing these galaxies naturally place thespectra into several classes defined by the plane formed by the first threeeigencoefficients of each spectrum. Spectral types, corresponding to differentHubble-types and galaxies with extreme emission lines, are identified for the170,000 spectra and are shown to be complementary to existing spectralclassifications. From a non-parametric classification technique, we find thatthe population of galaxies can be divided into three classes which correspondto early late- through to intermediate late-types galaxies. (Abridged)