Two high-velocity encounters of elliptical galaxies |
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| Authors: | Marc Balcells Kirk D Borne John G Hoessel |
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| Institution: | (1) Washburn Observatory, University of Wisconsin, Madison, Wis., USA |
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| Abstract: | We present the results of our study of two collisions of binary elliptical galaxies, NGC 4782/4783 and NGC 2672/2673. Each pair has a high relative velocity (>500 km s–1 along the line-of-sight) but the two pairs differ in mass ratio ( 1 for the first pair, and 10 for the second). CCD images and velocities obtained from digital spectra are used to constrain simulations of the galaxy collisions. Once a solution has been found and its uniqueness verified, we derive the binary orbital elements, the orientation of the orbit in the sky, the time since pericenter, and the dynamical mass of the pair. This method provides a quantitative determination of galaxy masses on the scale of the binary separations free from uncertainties due to projection effects. We also derive accurate timing of the collision and information about the fate of the pairs (merger/escape). Among our conclusions, we find that the dumb-bell galaxy NGC 4782/4783 isnot a supermassive galaxy as claimed from the high relative velocity and the high central dispersions, but has a moderateM/L
B10. Its trajectory has been changed from hyperbolic to elliptical as a result of energy lost during the collision. NGC 2672/2673 provides an interesting example of how the collision probes the internal structure and dynamics of a galaxy. It also has a moderateM/L
B7.Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., for the National Aeronautics and Space Administration, MA, U.S.A.Kitt Peak National Observatory, National Optical Astronomy Observatories, operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation, AR, U.S.A. |
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