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M. Boylan-Kolchin, C.-P. Ma, E. Quataert (UC Berkeley)
Several independent lines of evidence indicate that late-time, dissipationless mergers play a substantial role in assembling massive elliptical galaxies. These mergers can place interesting constraints on galaxy formation theories because of the very tight scaling relations low-redshift ellipticals are observed to obey. We use controlled N-body simulations to study these dissipationless mergers. Our initial galaxy models consist of a stellar bulge and a dark matter halo and include the effects of adiabatic contraction; we also vary the initial orbital energy and angular momentum to characterize the dependence of the merger remnant on the orbit. The orbital parameters determine how much energy is transfered from the bulge to the halo during the merging process, which in turn determines the bulge's scaling relations. We find that mergers on cosmologically probable orbits reproduce projections of the fundamental plane (the Faber-Jackson and stellar mass-size relations) while less probable orbits produce deviations from these relations. We also quantify the scatter induced in the scaling relations due to variations in viewing angle and compare with the scatter in the observed relations. Our simulations also have implications for the black hole M-\sigma relation, which we discuss. The dark matter fraction within one effective radius increases as a result of the merger, indicating that a systematic variation in dynamical to stellar mass can cause the observed tilt in the fundamental plane.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.