Gas dynamics and disk formation in 3 : 1 mergers

We performed N-body/SPH simulations of merging gas rich disk-galaxies with a mass ratio of 3:1. A stellar disk and bulge component and a dark halo is realized with collisionless particles, the gas is simulated using SPH particles. In this paper we focus on the gas dynamics in mergers and its influence on the structure of the final merger remnant, neglecting star formation. During the merger around 8 × 109M⊙ of gas accumulate in the central region of the merger remnant (inside 300 pc). Part of the gas falls to the center, channeled by a tidally induced bar in the more massive galaxy. A peak accretion rate of 150 solar masses/year is reached when the two galaxy centers merge. It is likely that the gas will experience a central starburst and/or fuel a central black hole. The gas in the outer regions accumulates in dense knots within tidal tails which could lead to the formation of open clusters or dwarf satellites. Later on, the gas knots loose angular momentum by dynamical friction and also sink to the center of the remnant, thereby increasing the central gas content. In the end, the gas settles in a central power-law disk with surface density Σ ∝ r surrounded by dense, orbiting gas clumps. The stellar profile is of de Vaucouleurs-type, like in simulations of pure stellar mergers 1. Initial Conditions and merger model The disk-galaxies are constructed in dynamical equilibrium (Hernquist, 1993) and consist of an exponential stellar and gaseous disk of the same mass, a bulge with a Hernquist-profile, and a pseudo-isothermal dark halo. The small galaxy has 1/3 of the mass and 1/3 of the particles of the massive one. The scale length is reduced by (1/3)1/2. In total we used 88888 collisionless particles and 26666 gas particles simulated using SPH with an isothermal equation of state. Both galaxies approach each other on nearly parabolic prograde orbits with slightly inclined disks relative to the orbital plane. The simulations were performed on a Sun ULTRA 60 workstation.