Dwarf Galaxy Collisional Experiments

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Session 48 -- Spiral, Dwarf and Irregular Galaxies
Display presentation, Wednesday, 1, 1994, 9:20-6:30

[48.20] Dwarf Galaxy Collisional Experiments

Lance K. Erickson (ERAU)

Gravitational perturbations were made on dwarf galaxy models to measure the internal motion and mean densities for later correlation with dwarf stellar activity. The models consist of 100,000 particles distributed as n=3 polytropes in two separate objects with a mass difference ranging from 10:1 to 100:1. To produce perturbations in the smaller, dwarf object, the larger object and dwarf were placed in collisional orbits. The larger (primary) model included a warm, rotating, equatorial disk component of 50% to 90% of the primary mass.

The $10^{5}$ particle experiments represented a total mass of $2x10^{11}M_{\sun}$, with each particle equivalent to $2x10^{6}M_{\sun}$. Although these numbers suggest individual particle masses of the order of molecular clouds, point-mass potentials were used in the N-body gridded mass potential code developed by Miller (Miller, Ap.J., 1978, 223, 122).

The density perturbations in the dwarf were assumed to follow the potential variation in the dwarf-primary encounter. Radial motion and density measurements verified this assumption, however, significant radial motion was also observed in the dwarf at formation. The initial dwarf radial pulsation exhibited a period of approximately 40 time steps, or $2x10^{8}$ years, and an amplitude of a few percent of the radius. The period of greatest potential variation occurs in the encounters as the dwarf passes through the disk structure; approximately 10 time steps, or $4x10^{7}$ years with approximately the same few-percent amplitude. Dwarf encounters with a primary model that does not have a disk shows less contraction in similar orbital encounters, and nearly complete disruption if the dwarf center passes closer than 0.7 of the primary object's outer radius.

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