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Title:
Thermal and Non-Thermal Radio Continuum Sources in the W51 Complex
Authors:
Moon, Dae-Sik; Koo, Bon-Chul
Affiliation:
AA(Department of Astronomy, Seoul National University, Korea), AB(Department of Astronomy, Seoul National University, Korea)
Publication:
Journal of the Korean Astronomical Society, vol. 27, no. 1, p. 81-102
Publication Date:
04/1994
Origin:
JKAS
Keywords:
RADIO COMPLEX: W51, RADIO CONTINUUM: THERMAL AND NON-THERMAL, ISM:HII REGIONS, SUPERNOVA REMNANT, MOLECULAR CLOUDS
Bibliographic Code:
1994JKAS...27...81M

Abstract

We have decomposed the 11-cm radio continuum emission of the W51 complex into thermal and non-thermal components. The distribution of the thermal emission has been determined by analyzing HI, CO and IRAS 60-micrometer data. We have found a good correlation between the 11-cm thermal continuum and the 60-micrometer emissions, which is used to obtain the thermal and non-thermal 11-cm continuum maps of the W51 complex. Most of the thermal continuum is emanating from the compact HII regions and their low-density ionized envelopes in W51A and W51B. All the HII regions, except G49.1-0.4 in W51B, have associated molecular clumps. The thermal radio continuum fluxes of the compact HII regions are proportional to the CO fluxes of molecular clumps. This is consistent with the previous results that the total mass of stars in an HII regions is proportional to the mass of associated molecular clump. According to our result, there are three non-thermal continuum sources in W51: G49.4-04 in W51A, a week source close to G49.2-03 in W51B, and the shell source W51C. The non-thermal flux of G49.5-04 at 11-cm is about 28 Jy, which is about 25% of its total 11-cm flux. The radio continuum spectrum between 0.15 and 300 GHz also suggests an excess emission over thermal free-free emission. We show that the excess emission can be described as a non-thermal emission with a spectral index alpha = -1.0 attenuated by thermal free-free absorptions at low frequencies. The non-thermal source close to G49.2-03 is week(about 9 Jy). the nature of the source is not known and the reality of the non-thermal emission needs to be confirmed. The non-thermal shell source W51C has a 11-cm flux of about 130 Jy and a spectral index alpha = -0.26

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