A high-resolution neutral-hydrogen study of the galaxy M81

Abstract

view Abstract Citations (103) References (37) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A high-resolution neutral-hydrogen study of the galaxy M81. Gottesman, S. T. ; Weliachew, L. Abstract A 2' synthesis of M81 (NGC 3031) has been made in the 21-cm neutral-hydrogen emission line. In addition to the interferometric data, a single-dish measurement provided information about the large-scale structure. One-third of the H I observed appears to be divorced from the main body of the galaxy and shows large non- circular motions. The satellite system DDO 66/Ho IX has been observed with an indicative total mass of 5 x 10 M0 of which percent is H I, assuming a distance of 3.25 Mpc to M81. The neutral-hydrogen content of this dwarf irregular galaxy is very high for its luminosity when compared with normal galaxies. The diffuse ring located north of M81 and first noted by Arp has 1.2 x 10 M0 of H I associated with it. The line-of-sight velocities in this feature are totally inconsistent with rotation in the main plane of M81. A rotation curve was established for M 81, and within 20 kpc of the center a mass of 1.1 x 1011 M0 is found. The neutral-hydrogen mass in M81 is 4.9 >c 10 M0. The disk of M81 shows strong noncircular motion in the vicinity of DDO 66/Ho IX. The spiral arms of the galaxy are resolved with a width of 2 kpc at a radial distance of 7-10 kpc from the center. In the same region the intrinsic contrast of the gas density of the arms is 3:1-5:1. Employing our new results, a density-wave model is discussed which appears to be in better agreement with the structure of the galaxy than the model using older optical data proposed by Shu et al. The kinematics of M81, as derived from our study, do not show the systematic pattern of noncircular velocities expected from the density-wave theory. However, the magnitude of these noncircular terms expected from our density-wave model are too small to be detected where the H I arms are well resolved. Subject headings: galaxies, individual - galaxies, motions in - 21-cm radiation Publication: The Astrophysical Journal Pub Date: January 1975 DOI: 10.1086/153301 Bibcode: 1975ApJ...195...23G Keywords: Galactic Radiation; Hydrogen Clouds; Radio Emission; Spatial Distribution; Spectral Emission; Astronomical Maps; Astronomical Models; Density Distribution; Galactic Structure; Radio Spectra; Astrophysics full text sources ADS | data products SIMBAD (5) NED (1)