How galaxies assembled from the primordial plasma and evolved to their present-day masses and shapes is a question of great interest to astrophysicists. A central issue is the dichotomy of galactic shapes: Why are most galaxies disk-shaped like our Milky Way, yet others--including the massive ellipticals in rich clusters of galaxies--are spheroidal or even triaxial? What determined whether a density perturbation of the early universe evolved into a present-day disk galaxy or an elliptical?

In search of answers, François Schweizer pursues observing programs aimed at studying galaxy assembly in nearby colliding and merging galaxies. Past research indicates that collisions and mergers are more frequent than was once thought and may, in fact, have been a dominant process in shaping galaxies and determining their present-day stellar and gaseous contents. Whereas mergers at low redshifts may only partially illustrate extreme phenomena that occurred in mergers of more gaseous galaxies at high redshifts, they can be studied in great detail and offer valuable clues about some of the processes at work.

One such process being investigated by Schweizer is the formation of new, second-generation globular clusters during major mergers. Having found that many of the luminous blue "knots" seen in colliding galaxies like NGC~4038/4039 are, in fact, young globular star clusters of relatively high metallicity, Schweizer is now studying possible connections between such merger-generated clusters and the reddish, metal-rich globulars found in elliptical and S0 galaxies. During the past year, he and co-investigators Bradley Whitmore, Michael Fall (both of the Space Telescope Science Institute), and Bryan Miller (Gemini Observatory) used the Hubble Space Telescope to obtain deep images of six E and S0 galaxies suspected of having formed through mergers during the past few billion years. The excellent spatial resolution of these images makes it relatively easy to separate candidate globular clusters in the host galaxies from images of Milky Way foreground stars and distant background galaxies, and a few hundred candidate globulars were found in each galaxy. Schweizer plans to do follow-up spectroscopy of these objects with the new Walter Baade telescope in order to determine their velocities, chemical compositions, and ages. Since the Baade spectrographs will cover a much wider field of view than the Hubble does, Schweizer and collaborator Patrick Seitzer of the University of Michigan used the du Pont telescope at Las Campanas to obtain supplementary wide-field images of the same galaxies and of hitherto unobserved merger remnants. The investigators hope that the end result of this 4 to 5 year program of Hubble photometry and Baade spectroscopy will be new information on how and when elliptical and S0 galaxies formed their metal-rich globular clusters.

In a related Northern-Hemisphere program, Schweizer, Seitzer, Jean Brodie of Lick Observatory, and her collaborators used the Keck telescope to continue collecting spectra of candidate globular clusters in the elliptical galaxy NGC 3610 and in NGC 3921, a remnant of two merged disk galaxies. All objects were confirmed to be globular clusters, and an analysis of their ages and compositions is in progress.