Astron. Astrophys. 355, 1115-1121 (2000)

1. Introduction

Since its discovery (Cheung et al. 1968), ammonia has been observed in the Galaxy via several transitions, particularly the metastable lines (J = K, K). The spectral lines of this molecule are a powerful tool to determine the physical conditions of the clouds and good tracers of dense molecular gas. Surveys of ammonia lines have been made from the northern hemisphere toward dark clouds (e.g. Myers & Benson 1983) and giant and ultra-compact HII regions (McDonald et al. 1981, Churchwell et al. 1990). However, only recently has an extended NH₃ survey been published toward dense condensations of the southern hemisphere dark clouds (Bourke et al. 1995a, b) and only a few positions have been observed toward HII regions (Jauncey et al. 1981, Scalise et al. 1981, Gardner et al. 1985, Vilas-Boas et al. 1988).

In this paper we present the results of a (J,K) = (1,1) survey toward 108 southern hemisphere HII regions. The selected positions are the peaks of H109 recombination line emission with temperatures larger than 0.05 K, observed by Wilson et al (1970). They represent roughly 73 % of the HII regions in the sample, which was compiled from three surveys of continuum sources at 6, 11 and 20 cm in the direction and .

© European Southern Observatory (ESO) 2000

Online publication: March 21, 2000
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