FOUR HIGHLY LUMINOUS MASSIVE STAR-FORMING REGIONS IN THE NORMA SPIRAL ARM. I. MOLECULAR GAS AND DUST OBSERVATIONS

Abstract

We report molecular line and dust continuum observations, made with the Swedish-ESO Submillimeter Telescope, toward four young high-mass star-forming regions associated with highly luminous (L > 6 × 105 L ) Infrared Astronomical Satellite sources (15290−5546, 15502−5302, 15567−5236, and 16060−5146). Molecular emission was mapped in three lines of CS (J = 2 → 1, 3 → 2, and 5 → 4), two lines of SiO (J = 2 → 1 and 3 → 2), two rotational transitions of CH3OH (Jk = 3k → 2k and 2k → 1k), and in the C34S(J = 3 → 2) line. In addition, single spectra at the peak position were taken in the CO(J = 1 → 0), 13CO(J = 1 → 0), and C18O(J = 1 → 0) lines. We find that the luminous star-forming regions are associated with molecular gas and dust structures with radii of typically 0.5 pc, masses of ∼5 × 103M , column densities of ∼5 × 1023 cm−2, molecular hydrogen densities of typically ∼2 × 105 cm−3, and dust temperatures of ∼40 K. The 1.2 mm dust continuum observations further indicate that the cores are centrally condensed, having radial density profiles with power-law indices in the range 1.9–2.3. We find that under these conditions dynamical friction by the gas plays an important role in the migration of high-mass stars toward the central core region, providing an explanation for the observed stellar mass segregation within the cores. The CS profiles show two distinct emission components: a bright component, with line widths of typically 5 km s−1 (FWHM), and a weaker and wider velocity component, which typically extends up to ±13 km s−1 from the ambient cloud velocity. The SiO profiles also show emission from both components, but the intensity of the pedestal feature relative to that of the bright component is stronger than for CS. The narrow SiO component is likely to trace warm ambient gas close to the recently formed massive stars, whereas the high velocity emission indicates mass outflows produced by either the expansion of the Hii regions, stellar winds, and/or collimated outflows. We find that the abundances of CS, CH3OH, and SiO, relative to H2, in the warm ambient gas of the massive cores are typically 4 × 10−8, 6 × 10−9, and 5 × 10−11, respectively.