The Fundamental Plane and Merger Scenario. I. Star Formation History of Galaxy Mergers and Origin of the Fundamental Plane

Abstract

We perform numerical simulations of galaxy mergers between star-forming and gas-rich spirals in order to explore the origin of the fundamental plane (FP) of elliptical galaxies. We consider, in particular, that the origin of the slope of the FP is essentially due to the nonhomology in the structure and kinematics of elliptical galaxies and, accordingly, investigate structural and kinematic properties of elliptical galaxies formed by dissipative galaxy merging with star formation. We found that the rapidity of star formation, which is defined as the ratio of dynamical timescale of a merger progenitor to the timescale of gas consumption by star formation, is a key determinant for nonhomology parameters, such as the density profile of the stellar component, the relative importance of global rotation in kinematics, and the ratio of total dynamical mass to luminous mass, in merger remnants. We furthermore found that this result does not depend so strongly on initial intrinsic spins of progenitor disks and orbital energy and angular momentum of mergers. These results strongly suggest that the structural and kinematic nonhomology observed in elliptical galaxies can be closely associated with the difference in star formation history between elliptical galaxies formed by dissipative galaxy merging. Based on these results, we discuss a close physical relation between the origin of the FP and the star formation history of elliptical galaxies.