G30.79 FIR 10: A gravitationally bound infalling high-mass star-forming clump

Abstract

Context. The process of high-mass star formation is still shrouded in controversy. Models are still tentative and current observations are just beginning to probe the densest inner regions of giant molecular clouds. Aims. The study of high-mass star formation requires the observation and analysis of high-density gas. This can be achieved by the detection of emission from higher rotational transitions of molecules in the sub-millimeter. Here, we studied the high-mass clump G30.79 FIR 10 by observing molecular emission in the 345 GHz band. The goal is to understand the gravitational state of this clump, considering turbulence and magnetic fields, and to study the kinematics of dense gas. Methods. We approached this region by mapping the spatial distribution of HCO+(J = 4 →) 3, H13CO+ (J = 4 → 3), CS(J = 7 → 6), 12CO(J = 3 → 2), and 13CO(J = 3 → 2) molecular emission by using the ASTE telescope and by observing the 12C18O(J = 3 → 2), HCN(J = 4 → 3), and H 13CN(J = 4 → 3) molecular transitions with the APEX telescope. Results. Infalling motions were detected and modeled toward this source. A mean infall velocity of 0.5 km s-1  with an infall mass rate of 5 × 10-3 M⊙ yr-1 was obtained. Also, a previously estimated value for the magnetic field strength in the plane of the sky was refined to be 855 μG which we used to calculate a mass-to-magnetic flux ratio, λ = 1.9, or super-critical. The virial mass from turbulent motions was also calculated finding Mmathrmvirr = 563 M⊙, which gives a ratio of Mmathrm/M\mathrmM vir = 5.9. Both values strongly suggest that this clump must be in a state of gravitational collapse. Additionally, we estimated the HCO+ abundance, obtaining X(HCO+) = 2.4 × 10-10. © 2010 ESO.