Orbital Structure of Merger Remnants. I. Effect of Gas Fraction in Pure Disk Mergers

Abstract

Since the violent relaxation in hierarchical merging is incomplete, elliptical galaxies retain a wealth of information about their formation pathways in their present-day orbital structure. Recent advances in integral field spectroscopy, multi-slit infrared spectroscopy, and triaxial dynamical modeling techniques have greatly improved our ability to harvest this information. A variety of observational and theoretical evidence indicates that gas-rich major mergers play an important role in the formation of elliptical galaxies. We simulate 1: 1 disk mergers at seven different initial gas fractions (f(gas)) ranging from 0% to 40%, using a version of the TreeSPH code Gadget-2 that includes radiative heating and cooling, star formation, and feedback from supernovae and active galactic nuclei. We classify the stellar orbits in each remnant and construct radial profiles of the orbital content, intrinsic shape, and orientation. The dissipationless remnants are typically prolate-triaxial, dominated by box orbits within r