Nature of the Radio Source W 49.

Abstract

The galactic radio source W 49 is an association of a giant H II region, a nonthermal source, and OH emission clouds. The nature of this source has been investigated using radio astronomical observaLions of both its continuum and associated line radiation. W 49 consists of the thermal component A (G 43.2+0.0) and the nonthermal component B(G 43.30.2). Both components are at about the same distance, 14.1 kpc, from the sun and a distance of about 10 kpc from the galactic center. The projected distance between the centers of components A and B is 12.5 min of arc or 51 pc. If the nonthermal component is a supernova remnant it must be a considerably older and originally much more powerful supernova remnant than Cassiopeia A. Both the analysis of the spectrum and high angular resolution observations of the brightness temperature distribution of the radio continuum of the thermal component A suggests that it consists of one or more high-density components A2 of small angular diameters (Os< 14"; N0> 1.2 X 10~ cm-3) which are embedded in a component Al of lower density and larger angular diameter (Os = 3.5'; N0 =271 cm-3). The high-density component A2- although different from any type of emission nebula known to date could be ionized by a star with Mv= -7.0 and T5=5.1040K. It is, however, doubtful if stars with this characteristics exist. It is more probable that component A2 consists of several high-density condensations, which can not be resolved with an angular resolution of 2 min of arc. The total thermal component A seems to be surrounded by a shell of neutral hydrnge~ which may contain as much as 3.3 X 10~ solar masses. Shell and H II region together from a gravitationally stable system, and could be a young 0 and B star association. Xonthermal emission of the 18 cm OH lines close to W 49 comes from two emission centers. There is a close correlation in the radial velocities of the OH emission lines and the lO9a recombination line emitted by the thermal component A of W 49. Our observations show that the projected positions of the two OH emission centers lie within the 30% contours of a contour map of component A observed at N= 1.95 cm with an angular resolution of 2'. The OH emission clouds seem to be located inside the low-density H II region Al and close to the high- density H II regions A2. The Xational Radio Astronomy Observatory is operated by Associated Universities, Inc., under contract with the Xational Science Foundation. The Arecibo Ionospheric Observatory is operated by Cornell University with the support of the Advanced Research Projects Agency under a research contract with the Air Force Office of Scientific Research OAR.