Hubble Space Telescope observations of two dynamically young elliptical galaxies

High-resolution images of the candidate dynamically young ellipticals NGC 1700 and NGC 3610 have been obtained with the WFPC2 of the Hubble Space Telescope. NGC 1700 contains approximately a dozen dust clouds arranged in a chaotic distribution near the center of the galaxy, suggestive of a merger or accretion event. NGC 3610 contains a remarkably twisted stellar disk within 2.7 '' (0.4 kpc for H-0 = 75) of the center, but no apparent dust features. The smooth, symmetric appearance of this disk and the lack of correlation with the color image suggest that it is a relaxed stellar component, possibly a disk twisted by differential precession. Its relevance to a past interaction remains unclear since the feature appears to be unique among ellipticals observed so far. A search for intermediate-age globular clusters formed during merger or accretion events reveals a population of clusters in NGC 3610 which are similar to 0.7 mag brighter in V, similar to 0.2 mag redder in V-I, and more centrally located than a typical old, metal-poor population. Simulations using Bruzual-Charlot (1996, in preparation) cluster evolution models suggest that the colors and magnitudes of these clusters are consistent with an age of 4 Gyr (assuming near-solar metallicity). However, spectroscopic measurements of the cluster metallicities will be needed to confirm this age estimate. In the case of NGC 1700 few if any new globular clusters seem to have formed during the accretion event that produced the loops and shells of this galaxy. Combining the present results with previous HST observations of other merger remnants shows generally good agreement between age estimates based on photometric, spectroscopic, and/or kinematic observations of the remnants, and age estimates based on the colors and luminosities of young and intermediate-age star clusters. (C) 1997 American Astronomical Society.