Neutral hydrogen in the Andromeda Nebula. III - The velocity field.

Details Neutral hydrogen in the Andromeda Nebula. III - The velocity field. Neutral hydrogen in the Andromeda Nebula. III - The velocity field.

Nov 1983

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983mnras.205..773u&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 205, Nov. 1983, p. 773-791.

Astronomy and Astrophysics

Astronomy

17

Andromeda Galaxy, Galactic Rotation, Hydrogen Clouds, Neutral Gases, Radial Velocity, Astronomical Maps, Density Wave Model, Galactic Nuclei, Galactic Structure, H Lines, Kinematics, Radio Galaxies

Scientific paper

The H I velocity field of the Andromeda Nebula (M31) has been observed using the Cambridge Half-Mile telescope, with a synthesized beam of 0.8 x 1.2 arcmin2 and a resolution in radial velocity of 16 km S-1. Contour maps of the radial velocities within 20 kpc of the nucleus are presented, and the dynamics of neutral hydrogen gas in the disc of the galaxy are discussed. These observations represent the most detailed kinematic information available on an external galaxy and they reveal complicated fine structure on scales of a few hundred parsecs. In many areas of the galaxy, velocity are double-peaked, indicating the presence of two systems of gas motion along the line-of-sight. By treating the velocity field as double-valued, confused spiral arms may be separated, and the geometry of the warp in the M31 disc deduced. Systematic deviations from simple rotation models of up to 50 km S-1 are found in the spiral arms; some of these are of the form predicted by the density-wave theory, but most are ambiguous. The measured rms velocity dispersion of 8.1 ± 0.9 km S-1 is independent of position in the galaxy when due allowance is made for complex velocity profiles. The H I disc thickness estimated by combining this value with a mass model for the disc places strong limits on the thickness of the stellar z-distribution.

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