Distribution and kinematics of neutral hydrogen in the spiral galaxies M81. I. Observations.
Abstract
Summary. In this paper we present observations of the early type spiral galaxy M 81 (NGC 3031) made with the Westerbork Synthesis Radio Telescope in the 21-cm line of neutral hydrogen. The angular resolution is 24" x 26" which, at a distance of 3.25 Mpc, corresponds to a linear resolution in the plane of the sky of 380 x 400 pc, or 400 x 800 pc in the plane of the galaxy. We confine ourselves to an area of 36' x 52'. A velocity range from -300 km/s to +320 km/s is covered at a resolution of 27 km/s. In Section 2 we describe the observations, in Section 3 the subsequent reduction of the data. In Section 4 we discuss the results briefly. A more detailed analysis will be presented in Paper II. In general there is a good qualitative agreement with the observations of Gottesman and Weliachew (1975). There is, however, an as yet unresolved discrepancy in the total amount of H I detected. The central regions exhibit a marked lack of H I. Between 3 and 10 kpc radius the distribution of H I shows a distinct regular two-armed spiral pattern. Outside 10 kpc two outer arm features develop. Within R = 13 kpc the eastern half of the galaxy contains about 50 % more H ithan the western half. At larger radii, on the eastern side of fhe galaxy, two large H I complexes are found. These may be part of a bridge connecting M 81 and M 82. Inside a radius of 10 kpc the velocity field is on the whole fairly regular, except for systematic non-circular motions in the spiral arms. Outside 10 kpc the velocity field is dominated by the non-circular motions of the two large H I complexes and the northern outer arm. Key words: neutral hydrogen - spiral galaxies - Messier8t
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- December 1975
- Bibcode:
- 1975A&A....45...25R
- Keywords:
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- Astronomical Maps;
- Density Distribution;
- Hydrogen;
- Kinematics;
- Line Spectra;
- Spiral Galaxies;
- Absorption Spectra;
- Brightness Temperature;
- Data Processing;
- Fast Fourier Transformations;
- Galactic Rotation;
- Radio Astronomy;
- Schmidt Cameras;
- Astrophysics