Observations of the southern Milky Way at 21 centimeters.
Abstract
Observations of 21-cm line radiation from the southern Milky Way are being carried out with the four-channel fixed-frequency receiver described by Kerr, Hindman and Robinson (1954). A tentative picture of the spiral structure in the southern portion of the conventional galactic plane was obtained from observations made during 1954. The current program covers an extended range of galactic latitude, 80 wide, with the object of obtaining the three-dimensional distribution of neutral hydrogen. Observations are made along selected paths which cross the galactic circle at a number of different longitudes. For each longitude a diagram showing constant-intensity contour lines with respect to galactic latitude and radial velocity is being derived. Since the velocity scale is related to a distance scale, a series of such diagrams leads to the space distribution, providing the ambiguities inside a circle through the sun can be resolved. Diagrams of this type in the longitude range 2600 to 2750 indicate that the outer spiral arms are trailing in this region, confirming the results obtained in the galactic plane. They show in addition an increasing southward shift in galactic latitude with increasing distance. Edmondson (1955) has recently suggested that the mean motions in the galaxy may depart from circular motion by about 40 This hypothesis can be tested by comparing radial velocities in the inner part of the galaxy, along lines of sight which are symmetrically placed relative to the galactic center. Comparisons which have been made so far between the Sydney and Leiden results at corresponding longitudes near the center do not appear to show the large velocity differences predicted by Edmondson's theory. Complications are produced, however, by local structural differences and by the different antenna beam widths used in the two sets of observations, and a firm conclusion must await a systematic comparison over a wide range of longitudes. Edmondsou, F. K. 1955, Pub. A. S. P. 67, 10. Kerr, F. J., Hindman, J. V. and Rohinsen, B. J. `954, Aust. J. Phys. 7, 297. Division of Radio physics, Commonwealth Scientific and Industrial Research Organization, Sydney, Australia
- Publication:
-
The Astronomical Journal
- Pub Date:
- February 1956
- DOI:
- 10.1086/107273
- Bibcode:
- 1956AJ.....61....7K