Optical Galactic Spiral Patterns as the Gas Response to a Rotating 2-Armed Stellar Spiral

Details Optical Galactic Spiral Patterns as the Gas Response to a Rotating 2-Armed Stellar Spiral Optical Galactic Spiral Patterns as the Gas Response to a Rotating 2-Armed Stellar Spiral

Sep 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aipc..784..362m&link_type=abstract

MAGNETIC FIELDS IN THE UNIVERSE: From Laboratory and Stars to Primordial Structures. AIP Conference Proceedings, Volume 784, pp

Computer Science

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Galaxy, Computer Aided Analysis, Interstellar Matter, Spiral Arms And Galactic Disk, Mathematical Procedures And Computer Techniques, Spiral Galaxies, Astronomical Catalogs, Atlases, Sky Surveys, Databases, Retrieval Systems, Archives, Etc.

Scientific paper

We report ongoing simulations of the gas response to a rigidly rotating spiral pattern in the non-self-gravitating hydrodynamic regime using the ZEUS code in a Galactic disk model. The disk model is a bidimensional projection of a 3D mass distribution representing the known axisymmetric Galactic components including a massive dark matter halo, and a spiral 2-armed pattern modelled following the locus and pitch angle of K-band observations in our Galaxy. We find that the isothermal gaseous response is a sensitive function of the pattern rotation speed Ωp. The same behavior was found in previous work for the dynamical self-consistency of the stellar orbital structure, for this model of the Milky Way. Here we studied the response as a function of Ωp and the pattern termination placed at different galactocentric radii R (12 kpc, corotation, and the 4:1 resonance) to test known theoretical predictions for the extent of spiral arms according to their strength. Our results suggest that the Milky Way is a weak spiral, with its gaseous pattern ending at corotation; however, there are as well indications of an abrupt fall off in density along the spiral, in agreement with infrared data analysis. The spiral mass, hence the forcing, was also varied within plausible values for a Sb galaxy. The response to the 2-armed stellar pattern is a 4-armed gaseous pattern for Ωp of 20 km s-1 kpc-1. Values close to this optimal Galactic (dynamically self-consistent) rotation speed present similar bifurcations of the arms. Except possibly for very high forcing, low rotation speeds of 10 km s-1 kpc-1 or so lead to a gas response that only mimics the imposed 2-armed pattern and there are no arm bifurcations. For values of Ωp higher than 20 km s-1 kpc-1, a complex multi-arm response is produced. While most cases explored rapidly reach steady state (in timescales of the order 300 Myr or less) and maintained it to elapsed times of the order 3 Gyr, the high spiral mass case at that elapsed time is an oval inner dense structure of an oscillatory nature in the rotating pattern frame, where all calculations were performed.

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