Scaling Relations in Dissipationless Spiral-like Galaxy Mergers

Abstract

We determine both representations of the Fundamental Plane [Re Sig^a Ie^b and Re (Sig^2/Ie)^lambda] and the luminosity-effective phase space density [L fe^(-gamma)] scaling relation for N-body remnants of binary mergers of spiral-like galaxies. The main set of merger simulations involves a mass-ratio of the progenitors in the range of about 1:1 to 1:5, harboring or not a bulge-like component, and are constructed using a cosmological motivated model. Equal-mass mergers are also considered. Remnants lead to average values for the scaling indices of <a>~1.6, <b>~0.6, <lambda>~0.7, and <gamma>~0.65. These values are consistent with those of K--band observations (Mobasher et al. 1999) of ellipticals: <a>~1.5, <b>~0.8, <lambda>~0.7, and <gamma>~0.60. The b index is, however, not well reproduced. This study does not allow us to establish a conclusive preference for models with or without a bulge as progenitors. Our results indicate that the L--fe and FP scalings might be determined to a large extent by dissipationless processes, a result that appears to be in contradiction to other dissipationless results.