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We report molecular line and dust continuum observations, made with the SESTtelescope, towards four young high-mass star forming regions associated withhighly luminous (L> 6x10^5 Lsun) IRAS sources (15290-5546, 15502-5302,15567-5236 and 16060-5146). Molecular emission was mapped in lines of CS(J=2-1, 3-2 and 5-4), SiO (J=2-1 and 3-2), CH3OH (Jk=3k-2k and 2k-1k), and C34S(J=3-2). In addition, single spectra at the peak position were taken in the CO,13CO and C18O (J=1-0) lines. We find that the luminous star forming regions areassociated with molecular gas and dust structures with radii of typically 0.5pc, masses of ~5x10^3 Msun, column densities of ~5x10^{23} cm^{-2}, molecularhydrogen densities of typically ~2x10^5 cm^{-3} and dust temperatures of ~40 K.The 1.2 mm dust continuum observations further indicate that the cores arecentrally condensed, having radial density profiles with power-law indices inthe range 1.6-1.9. We find that under these conditions dynamical friction bythe gas plays an important role in the migration of high-mass stars towards thecentral core region, providing an explanation for the observed stellar masssegregation within the cores.

Four highly luminous massive star forming regions in the Norma Spiral Arm.: I. Molecular gas and dust observations