THE POST-MERGER ELLIPTIC NGC-1700 - STELLAR KINEMATIC FIELDS TO 4 EFFECTIVE RADII

We have measured the stellar motions in the elliptical galaxy NGC 1700 along four position angles, to very large radii, using absorption fea tures in spectra obtained with the Multiple Mirror Telescope. Our data extend the coverage of the stellar velocity field by a factor of 5 (2 .5 times further in radius and twice as many PAs) beyond previous work . We have attained 10 km s(-1) accuracy in the mean velocity V out to nearly 2 effective radii (r(e)), and errors are < 15% of the maximum r otation speed out to nearly 3 r(e). The lack of detectable minor-axis rotation and the nearly identical kinematics on the +/-45 degrees PAs suggest that NGC 1700 is nearly oblate for r less than or similar to 2 .5r(e). Beyond this radius, twisting of the morphological and kinemati c axes indicate increasing triaxiality, an intrinsic twist, or both. T he velocity distribution in the low-amplitude counterrotating core is weakly skewed in the direction of rotation, arguing against a central stellar disk. The small skewness and the depression of the central vel ocity dispersion are consistent with the accretion of a low-mass stell ar companion in a retrograde orbit. Photometric fine structure at larg e radii (Schweizer & Seltzer 1992) is also indicative of a merger; a v elocity reversal similar to 50'' northeast suggests a major event. How ever, radially increasing prograde rotation in the main body of the ga laxy implies that this was not the same event responsible for the coun terrotating core. The strong rotation at large R and the nearly oblate shape are consistent with N-body simulations of group mergers (Well 1 995); that all disturbances inside similar to 2.5r(e) have phase-mixed out suggests that NGC 1700 owes its present form to a merger of 3 or more stellar systems 2 - 4h(-1) Gyr ago. (C) 1996 American Astronomica l Society.