Equal-mass Mergers Research Articles

The line-of-sight velocity distributions of simulated merger remnants

We use Gauss-Hermite functions to study the line of sight velocity distributions in simulated merger remnants. Our sample contains sixteen remnants; eight produced by mergers between disk galaxies of equal mass and eight produced by mergers between disk galaxies with mass ratios of 3:1. The equal-mass mergers display a wide range of kinematic features, including counterrotation at large radii, orthogonally rotating cores, and misaligned rotational axes. Most of the unequal-mass remnants exhibit fairly regular disk-like kinematics, although two have kinematics more typical of the equalmass remnants. Our results may be compared to observations of early type objects, including ellipticals with misaligned kinematic axes, counterrotating systems, and S0 galaxies.

On the Formation of Boxy and Disky Elliptical Galaxies

The origin of boxy and disky elliptical galaxies is investigated. The results of two collisionless N-body simulations of spiral-spiral mergers with mass ratios of 1 : 1 and 3 : 1 are discussed, and the projected properties of the merger remnants are investigated. It is shown that the equal-mass merger leads to an anisotropic, slowly rotating system with preferentially boxy isophotes and significant minor-axis rotation. The unequal-mass merger results in the formation of a rotationally supported elliptical galaxy with disky isophotes and small minor-axis rotation. The observed scatter in the kinematical and isophotal properties of both classes of elliptical galaxies can be explained by projection effects.

Simulations of galaxy mergers

We present a number of N-body simulations of mergers of equal and unequal galaxies. A new code is presented which determines the potential from a mass distribution by a fourth-order expansion in Tesseral harmonics in three dimensions as an approximation to a collisionless system. The total number of particles in the system is 1200. Two galaxies, each a spherical non-rotating system with isothermal or Hubble density profile, are put in orbit around each other where tidal effects and dynamical friction lead to merging. The final system has a Hubble profile, and in some mergers an ‘isothermal’ halo forms as found in cD galaxies. Equal mass mergers are more flattened than unequal mass mergers. The central surface brightness decreases except in a merger of isothermal galaxies which shows a major redistribution of energy towards a Hubble profile. Mixing is severe in equal mass mergers, where radial gradients are weakened, while in unequal mass encounters gradients can build up due to less mixing and the formation of a halo. Oblate systems with strong rotation form in high angular momentum encounters while prolate systems with little rotation are formed in near head-on collisions.