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A High-Resolution 21-CM Hydrogen-Line Survey of the Andromeda Nebula

1966; IOP Publishing; Volume: 144; Linguagem: Inglês

10.1086/148645

1538-4357

Morton S. Roberts,

Astronomy and Astrophysical Research

view Abstract Citations (120) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A High-Resolution 21-CM Hydrogen-Line Survey of the Andromeda Nebula Roberts, Morton S. Abstract A survey of 21-cm hydrogen-line radiation was made over the central 2" of the Andromeda Nebula (M31). The observations were obtained with a 20-channel receiver and the 300-foot radio telescope; at 21 cm the beam width of this telescope is 10', which corresponds to 2 kpc at the distance of M31. Among the results derived are: a map of the radial-velocity field, the rotation-curve, the total mass, and the distribution of the integrated brightness temperature. The radial-velocity map for M31 displays a striking diagonal symmetry-one pair of quadrants agrees quite well with predictions from a model based on a thin disk in pure rotation while the other pair is in marked disagreement with such a model. An over-all expansion or contraction on a galactic scale cannot explain these features. The most direct explanation of the complex regions is in terms of bends at the ends of the hydrogen distribution similar to those found in our own Galaxy. The positions of loci of constant radial velocity near the minor axis require an additional mechanism for their explanation; a combination of expansion and contraction over various parts of M31 appears necessary. A rotation-curve was derived from data points in the "ordered" quadrants. The two halves of this rotation-curve are not symmetrical; this has been noted previously by Burke, Turner, and Tuve. The average total mass derived from the two quadrants as well as the mass computed from the combined (reflected) data is 3.1 X 1011 O. The systemic radial velocity derived from the rotation-curve is -310 km/sec. A comparison is made between Mayall's optically derived radial velocities and the 21-cm data. There is qualitative agreement between his measures and the complex-region data. Over the region common to the present study, his measures are of emission regions confined exclusively to the complex regions. The integrated hydrogen distribution shows a clear ringlike shape of 10 kpc radius with a distinct minimum in the central regions of Andromeda. A comparison between the locations of the peak H I ridge line and the distribution of emission nebulae mapped by Baade and Arp shows good general agreement. The H I distribution is, however, shifted west by 1' with respect to the concentrations of H ii regions. This displacement could be attributed to uncertainties in the 300-foot telescope pointing corrections only by invoking the combined maximum errors in right ascension and declination. There is thus a high probability that there is a displacement in the plane of up to 1 kpc between the optical spiral features and the location of the peak hydrogen concentrations. Publication: The Astrophysical Journal Pub Date: May 1966 DOI: 10.1086/148645 Bibcode: 1966ApJ...144..639R full text sources ADS | data products SIMBAD (1) NED (1)