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

P. C. Cortes^1,2, R. Parra³, J. R. Cortes² and E. Hardy²

¹ Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile e-mail: pcortes@astro.puc.cl
² National Radio Astronomy Observatory, Joint ALMA Office, Apoquindo 3846 piso 19, Las Condes, Santiago, Chile
³ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile

Received: 13 October 2008
Accepted: 10 June 2010

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 H¹³CN(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  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 = 563 , which gives a ratio of / = 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.