The orientation of elliptical galaxies

We determine the orientations of the light distribution of individual elliptical galaxies by combining the profiles of photometric data from the literature with triaxial models. The orientation is given by a Bayesian probability distribution. The likelihood of obtaining the data from a model is a function of the parameters describing the intrinsic shape and the orientation. Integrating the likelihood over the shape parameters, we obtain the estimates of the orientation. We find that the position angle difference between the two suitably chosen points from the profiles of the photometric data plays a key role in constraining the orientation of the galaxy. We apply the methodology to a sample of ten galaxies. The alignment of the intrinsic principle axes of the NGC 3379, 4486 and NGC 5638 are studied.Comment: accepted in Astrophysics and Space Scienc

The post-merger elliptical NGC 1700: Stellar kinematic fields to four effective radii

We have measured the stellar motions in the elliptical galaxy NGC 1700 along four position angles, to very large radii, using absorption features 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 (re), and errors are <15% of the maximum rotation speed out to nearly 3 re. The lack of detectable minor-axis rotation and the nearly identical kinematics on the ±45° PAs suggest that NGC 1700 is nearly oblate for r≲2.5re. Beyond this radius, twisting of the morphological and kinematic axes indicate increasing triaxiality, an intrinsic twist, or both. The 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 velocity dispersion are consistent with the accretion of a low-mass stellar companion in a retrograde orbit. Photometric fine structure at large radii (Schweizer & Seitzer 1992) is also indicative of a merger; a velocity reversal ∼50″ northeast suggests a major event. However, radially increasing prograde rotation in the main body of the galaxy implies that this was not the same event responsible for the counterrotating core. The strong rotation at large R and the nearly oblate shape are consistent with N-body simulations of group mergers (Weil 1995); that all disturbances inside ∼2.5re 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