Physical Characteristics Of G331.5-0.1: The Luminous Central Region Of A Giant Molecular Cloud
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We report molecular line and dust continuum observations toward the high-mass star-forming region G331.5-0.1, one of the most luminous regions of massive star formation in the Milky Way, located at the tangent region of the Norma spiral arm, at a distance of 7.5 kpc. Molecular emission was mapped toward the G331.5-0.1 GMC in the CO(J = 1 -> 0) and (CO)-O-18(J = 1. 0) lines with NANTEN, while its central region was mapped in CS(J = 2 -> 1 and J = 5 -> 4) with SEST, and in CS(J = 7 -> 6) and (CO)-C-13(J = 3 -> 2) with ASTE. Continuum emission mapped at 1.2 mm with SIMBA and at 0.87 mm with LABOCA reveal the presence of six compact and luminous dust clumps, making this source one of the most densely populated central regions of a GMC in the Galaxy. The dust clumps are associated with molecular gas and they have the following average properties: size of 1.6 pc, mass of 3.2 x 10(3)M(circle dot), molecular hydrogen density of 3.7 x 10(4) cm(-3), dust temperature of 32 K, and integrated luminosity of 5.7 x 10(5) L-circle dot, consistent with values found toward other massive star-forming dust clumps. The CS and (CO)-C-13 spectra show the presence of two velocity components: a high-velocity component at similar to-89 km s(-1), seen toward four of the clumps, and a low-velocity component at similar to-101 km s(-1) seen toward the other two clumps. Radio continuum emission is present toward four of the molecular clumps, with spectral index estimated for two of them of 0.8 +/- 0.2 and 1.2 +/- 0.2. A high-velocity molecular outflow is found at the center of the brightest clump, with a line width of 26 km s(-1) (FWHM) in CS(J = 7 -> 6). Observations of SiO(J = 7 -> 6 and J = 8. 7), and SO(J(K) = 8(8) -> 7(7) and J(K) = 8(7) -> 7(6)) lines provide estimates of the gas rotational temperature toward this outflow > 120 K and > 75 K, respectively.