Physics
Scientific paper
Jul 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990nascp3084...21r&link_type=abstract
In NASA, Ames Research Center, The Interstellar Medium in External Galaxies: Summaries of Contributed Papers p 21-22 (SEE N91-14
Physics
Gas Density, Hydrogen, Neutral Gases, Spiral Galaxies, Very Large Array (Vla), Asymmetry, Brightness Temperature, Mass To Light Ratios, Milky Way Galaxy, Radii, Sensitivity, Temperature Distribution, Thickness
Scientific paper
Very Large Array (VLA) observations of the neutral hydrogen (HI) gas in two nearby edge-on spirals (NGC 4565 and NGC 891) successfully resolve the thickness of the gas layers in both disks over a wide range in radii. The combination of B, C, and D array data produces a 4 arcsec (approx. 200 pc) beam and 21 km s-1 velocity resolution, combined with sensitivity to structures as large as 18 arcmin (approx. 54 kpc). These observations directly constrain the mid-plane disk mass densities, under the assumption of an equilibrium between the thermal pressure of the gas and the gravitational attraction of the disk. The results of a preliminary analysis are given regarding the z-velocity dispersion of the gas, the mass-to-light ratio of the disk in NGC 4565, and the roles of atomic and molecular gases. The data also allow a detailed study of the HI in these galaxies; in general their brightness temperature distributions seem similar to that in the Milky Way. Both galaxies show asymmetric HI extensions beyond the optical disk. In NGC 4565 the extension is a surprisingly abrupt warp, which may bend back to parallel the galactic plane; the velocity structure implies the warp is continuous around the disk.
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