The three-dimensional mass distribution in NGC 1700

A variety of modeling techniques is used with surface photometry from the l iterature and recently acquired high-accuracy stellar kinematic data to con strain the three-dimensional mass distribution in the luminous cuspy ellipt ical galaxy NGC 1700. First, we model the radial velocity field and photome try and, using a Bayesian technique, estimate the triaxiality T and short-t o-long axis ratio c in five concentric annuli between approximately 1 and 3 effective radii. The results are completely consistent with T being consta nt inside about 2.5r(e) (36 "; 6.7 h(-1) kpc). Adding an assumption of cons tant T as prior information gives an upper limit of T < 0.16 (95% confidenc e); this relaxes to T < 0.22 if it is also assumed that there is perfect al ignment between the angular momentum and the galaxy's intrinsic short axis. Near axisymmetry permits us then to use axisymmetric models to constrain t he radial mass profile. Using the Jeans (moment) equations, we demonstrate that two-integral, constant-M/L models cannot fit the data; but a two-integ ral model in which the cumulative enclosed M/L increases by a factor of sim ilar to 2 from the center out to 12 h(-1) kpc can. Three-integral models co nstructed by quadratic programming show that, in fact, no constant-M/L mode l is consistent with the kinematics. Anisotropic three-integral models with variable M/L, while not uniquely establishing a minimum acceptable halo ma ss, imply, as do the moment models, a cumulative M/L-B approximate to 10 h at 12 h(-1) kpc. We conclude that NGC 1700 represents the best stellar dyna mical evidence to date for dark matter in elliptical galaxies.