The effects of feedback in simulations of disk-galaxy major mergers

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  • 9 March 2005
Abstract
Using hydrodynamic simulations of disk-galaxy major mergers we investigate the star-formation history and remnant properties when various parameterizations of a simple stellar feedback model are implemented. The simulations include radiative cooling, a density-dependent star-formation recipe and a model for feedback from massive stars. The feedback model stores supernova feedback energy within individual gas particles and dissipates this energy on a time-scale specified by two free parameters; beta, which sets the efficiency, and n, which sets the effective equation of state in star-forming regions. Using a self-consistent disk galaxy, modeled after a local Sbc spiral, in both isolated and major-merger simulations, we investigate parameterizations of the feedback model. Model parameters are selected by requiring quiescent disk stability and star formation that is consistent with the Schmidt law found by Kennicutt (1998). Models that satisfy these criteria produce varying star-formation histories for disks evolved in isolation, or during a major merger. All major mergers produce a population of new stars that is highly centrally concentrated, demonstrating a distinct break in the r^{1/4} surface density profile, consistent with previous findings. The half-mass radius and one-dimensional velocity dispersion are affected by the feedback model used. We perform tests addressing the numerical resolution, the effects of star-formation normalization, the version of smoothed particle hydrodynamics (SPH) employed, and assumptions about the interstellar medium. Our results suggest previous simulations overpredicted the efficiency of star formation due to major mergers.

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