S. T. Gottesman

The Two Pattern Speeds of NGC 3359

Abstract: Using both observations and theoretical techniques, we show that the barred spiral galaxy NGC 3359 contains two pattern speeds. The faster pattern speed for the bar is obtained from isophotal analysis and stellar orbit theory. To explain the spiral arms and the observed velocity field of the disk, a slower pattern speed is required. Nonlinear resonance coupling is the supporting theory for the existence of two pattern speeds for the galaxy. The best match of our models with the observed data indicates a pattern speed for the bar of 39.17 km·sec−1∼kpc−1 and a value between 10 and 16 km·sec−1·kpc−1 for the spiral.

Mass Ditribution in Spiral Galaxies II

The VLA telescope was used to observe the atomic hydrogen emission from the Magellanic Cloudlike satellite surrounding several large spiral galaxies. The disks of these systems were resolved and their rotation masses were determined. The satellite kinematics were analyzed to determine an orbital mass in a volume of an average about 3.5 times that of the disk. Simulations were carried out on models on two kinds of models: those in which the satellite orbits were constrained to remain within the halo and those for which the constraint was not imposed. The most successful models have halo radii three to four times the disk radii of their primaries and their satellites have orbital eccentricities less than 0.3. The ratio of halo mass to disk mass is less than five with an average mass of about three disk masses. The observation that most of the satellites are undamaged militates against model galaxies with large halos and satellites with moderately eccentric orbits. 15 refs.