Interferometric multi-wavelength (sub) millimeter continuum study of the young high-mass protocluster IRAS 05358+3543

Aims. We study the small-scale structure of massive star-forming regions through interferometric observations in several ( sub) mm wavelength bands. These observations resolve multiple sources, yield mass and column density estimates, and give information about the density profiles as well as the dust and temperature properties. Methods. We observed the young massive star-forming region IRAS 05358+3543 at high spatial resolution in the continuum emission at 3.1 and 1.2mm with the Plateau de Bure Interferometer, and at 875 and 438 mu m with the Submillimeter Array. The observations are accompanied by VLA 3.6 cm archival continuum data. Results. We resolve at least four continuum sub-sources that are likely of protostellar nature. Two of them are potentially part of a proto-binary system with a projected separation of 1700 AU. Additional ( sub) mm continuum peaks are not necessarily harboring protostars but maybe caused by the multiple molecular outflows. The spectral energy distributions ( SEDs) of the sub-sources show several features. The main power house mm1, which is associated with CH3OH maser emission, a hypercompact HII region and a mid-infrared source, exhibits a typical SED with a free-free emission component at cm and long mm wavelengths and a cold dust component in the ( sub) mm part of the spectrum ( spectral index between 1.2mm and 438 mu m m alpha similar to 3.6). The free-free emission corresponds to a Lyman continuum flux of an embedded 13 M-circle dot B1 star. The coldest source of the region, mm3, has alpha similar to 3.7 between 1.2 mm and 875 mu m, but has lower than expected fluxes in the shorter wavelength 438 mu m band. This turnover of the Planck-function sets an upper limit on the dust temperature of mm3 of approximately 20 K. The uv-data analysis of the density structure of individual sub-cores reveals distributions with power-law indices between 1.5 and 2. This resembles the density distributions of the larger-scale cluster-forming clump as well as those from typical low-mass cores.