The evolution of the galaxy populations in rich clusters of galaxies is strongly dependent on the ability to discriminate between morphological classes along the Hubble sequence. Recent studies have used visual morphological classification by several individuals, with some systematic differences found among various classifiers and in the ultimate results. Here, a different approach is used: the ratio of bulge to total luminosity B/T is measured using detailed photometric profiles from HST/WFPC-2 images of a magnitude-limited sample of galaxies, most with spectroscopic confirmation of membership, in cluster MS1358+62 at z=0.33. These measurements of B/T are used as an indicator of galaxy morphological classification. The galaxies in this cluster have been visually classified independently by A. Dressler and D. Fabricant et al. The measured B/T values follow a similar relationship with morphological type in the cluster at z=0.33 as has been found for galaxies in the local universe, implying that B/T can be used as an indicator of morphological type. Both visual classifications show clear distinctions in mean < B/T> between major morphological classes (e.g., E versus S0), but are unable statistically to distinguish intermediate morphological classes (e.g., E/S0) from the major classes, at least as indicated by < B/T >. The detectability of evolution in the morphological mix is discussed in light of these results. An improved indicator, the cumulative distribution in B/T, is suggested to study this evolutionary signature with higher precision once suitable local samples of cluster galaxies can be assembled. This work has been supported by NASA from HST archival grant AR-08766.01-A and Hubble Fellowship grant HF-01099.01-97A from STScI.
American Astronomical Society Meeting Abstracts
- Pub Date:
- December 2000