2008A&A...485..497S

The goal of this work is to characterize the millimeter and centimeter properties of intermediate/high mass young stellar objects (YSOs) to search for any evolutionary trends.We carried out observations at 1.2mm with the IRAM 30m telescope, and at 3.6 and 1.3cm with the VLA toward a sample of 11 luminous (>10³L_☉) IRAS sources classified as high mass protostellar object candidates. The most promising regions additionally were observed at 7mm with the VLA. The 1.2mm emission, tracing the dust core in which the massive YSO is forming, shows a clear peak surrounded by some substructure in most cases, while in others it is very extended and weak. The masses from the 1.2mm data range from 10 to 140M_☉. For all (but one) of the sources, we detected centimeter emission associated with the IRAS source, with spectral indices between 3.6 and 1.3cm typical of optically thin emission, and deconvolved sizes from <0.01 to 0.3pc, suggesting that the emission comes from compact or ultra-compact (UC) HII regions. The physical parameters of the UCHII regions indicate that the ionizing stars are early B-type. The 7mm emission is partially resolved for the four regions observed at this wavelength, and we estimated the contribution of the dust emission to the 7mm flux density, ranging from negligible to 45%. By combining our data with infrared surveys, we built the spectral energy distribution and fitted a modified blackbody law. We found dust temperatures between 25 and 35K, dust emissivity indices between 1.5 and 2.2, and masses similar to the masses derived from the 1.2mm continuum emission. In addition, we found a correlation between the degree of disruption of the natal cloud, estimated from the fraction of dust emission associated with the centimeter source relative to the total amount of dust in its surroundings, and the size of the centimeter source.From the correlation found, we established an evolutionary sequence in which sources with compact millimeter emission clearly associated with compact centimeter emission are younger than sources with the millimeter emission dispersed and with the centimeter emission extended. Such a sequence is consistent with the evolutionary stage expected from maser/outflow/dense gas emission reported in the literature, and with the infrared excess of the 2MASS sources associated with the centimeter source.