Measuring galaxy potentials using shell kinematics
Abstract
We show that the kinematics of the shells seen around some elliptical galaxies provide a new, independent means for measuring the gravitational potentials of elliptical galaxies out to large radii. A numerical simulation of a set of shells formed in the merger between an elliptical and a smaller galaxy reveals that the shells have a characteristic observable kinematic structure, with the maximum line-of-sight velocity increasing linearly as one moves inward from a shell edge. A simple analytic calculation shows that this structure provides a direct measure of the gradient of the gravitational potential at the shell radius. In order to extract this information from attainable data, we have also derived a complete distribution of line-of-sight velocities for material within a shell; comparing the observed spectra of a shell to a stellar template convolved with this distribution will enable us to measure the gradient of the potential at this radius. Repeating the analysis for a whole series of nested shells in a galaxy allows the complete form of the gravitational potential as a function of radius to be mapped out. The requisite observations lie within reach of the up-coming generation of large telescopes.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 1998
- DOI:
- 10.1046/j.1365-8711.1998.01625.x
- arXiv:
- arXiv:astro-ph/9803053
- Bibcode:
- 1998MNRAS.297.1292M
- Keywords:
-
- GRAVITATION;
- METHODS: ANALYTICAL;
- METHODS: NUMERICAL;
- GALAXIES: ELLIPTICAL AND LENTICULAR;
- CD;
- GALAXIES: KINEMATICS AND DYNAMICS;
- Astrophysics
- E-Print:
- 6 pages, LaTeX, including 3 figures, using mn and epsf style files. Accepted for publication in MNRAS