Different evolutionary stages in massive star formation. Centimeter continuum and H O maser emission with ATCA

Received; accepted Aims. We present ATCA observations of the H2O maser line and radio continuum at 18.0 GHz and 22.8 GHz, toward a sample of 192 massive star forming regions containing several clumps already imaged at 1.2 mm. The main aim of this study is to investigate the water maser and centimeter continuum emission (likely tracing thermal free-free emission) in sources at different evolutionary stages, using the evolutionary classifications proposed by Palla et al. (1991) and Molinari et al. (2008). Methods. We used the recently comissioned CABB backend at ATCA obtaining images with ∼20 ′ ′ resolution in the 1.3 cm continuum and H2O maser emission, in all targets. For the evolutionary analysis of the sources we used the millimeter continuum emission from Beltrán et al. (2006) and the infrared emission from the MSX Point Source Catalogue. Results. We detect centimeter continuum emission in 88 % of the observed fields with a typical rms noise level of 0.45 mJy beam−1. Most of the fields show a single radio continuum source, while in 20 % of them we identify multiple components. A total of 214 centimeter continuum sources have been identified, likely tracing optically thin H ii regions, with physical parameters typical of both extended and compact H ii regions. Water maser emission was detected in 41 % of the regions, resulting in a total of 85 distinct components. The low angular (∼20 ′′) and spectral (∼14 km s−1) resolutions do not allow a proper analysis of the water maser emission, but suffice to investigate its association with the continuum sources. We have also studied the detection rate of H ii region