The G305 star-forming complex: radio continuum and molecular line observations

Abstract

We present 109–115 GHz (3 mm) wide-field spectral line observations of 12CO, 13CO and C18O J = 1–0 molecular emission and 5.5 and 8.8 GHz (6 and 3 cm) radio continuum emission towards the high-mass star-forming complex known as G305. The morphology of G305 is dominated by a large evacuated cavity at the centre of the complex driven by clusters of O stars surrounded by molecular gas. Our goals are to determine the physical properties of the molecular environment and reveal the relationship between the molecular and ionized gas and star formation in G305. This is in an effort to characterize the star-forming environment and constrain the star formation history in an attempt to evaluate the impact of high-mass stars on the evolution of the G305 complex. Analysis of CO emission in G305 reveals 156 molecular clumps with the following physical characteristics; excitation temperatures ranging from 7 to 25 K, optical depths of 0.2–0.9, H2 column densities of 0.1–4.0 × 1022 cm−2, clump masses ranging from 102 to 104 M⊙ and a total molecular mass of >3.5 × 105 M⊙. The 5.5 and 8.8 GHz radio continuum emission reveals an extended low surface brightness ionized environment within which we identify 15 large-scale features with a further eight smaller sources projected within these features. By comparing to mid-infrared emission and archival data, we identify nine H ii regions, seven compact H ii regions, one UC H ii region and four extended regions. The total integrated flux of the radio continuum emission at 5.5 GHz is ∼180 Jy corresponding to a Lyman continuum output of 2.4 × 1050 photons s−1. We compare the ionized and molecular environment with optically identified high-mass stars and ongoing star formation, identified from the literature. Analysis of this data set reveals a star formation rate of 0.008–0.016 M⊙ yr−1 and efficiency of 7–12 per cent, allows us to probe the star formation history of the region and discuss the impact of high-mass stars on the evolution of G305.