Rotating toroids in G10.62–0.38, G19.61–0.23, and G29.96–0.02^⋆

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: mbeltran@arcetri.astro.it
² IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France

Received: 26 May 2010
Accepted: 1 October 2010

Abstract

Context. In recent years, we have detected clear evidence of rotation in more than 5 hot molecular cores (HMCs). Their identification is confirmed by the fact that the rotation axes are parallel to the axes of the associated bipolar outflows. We have now pursued our investigation by extending the sample to 3 known massive cores, G10.62–0.38, G19.61–0.23, and G29.96–0.02.

Aims. We wish to make a thorough study of the structure and kinematics of HMCs and corresponding molecular outflows to reveal possible velocity gradients indicative of the rotation of the cores.

Methods. We carried out PdBI observations at 2.7 and 1.4 mm of gas and dust with angular resolutions of  ~2′′–3′′ and  ~1′′–2′′, respectively. To trace both rotation and expansion, we simultaneously observed CH₃CN, a typical HMC tracer, and ¹³CO, a typical outflow tracer.

Results. The CH₃CN (12–11) observations reveal clear velocity gradients in the three HMCs oriented perpendicular to the direction of the bipolar outflows. For G19 and G29 the molecular outflows have been mapped in ¹³CO. The gradients are interpreted as rotating toroids. The rotation temperatures, used to derive the mass of the cores, have been obtained by means of the rotational diagram method, and lie in the range of 87–244 K. The diameters and masses of the toroids lie in the range of 4550–12600 AU and 28–415 M_⊙, respectively. Given that the dynamical masses are 2 to 30 times lower than those of the cores (if the inclination of the toroids with respect to the plane of the sky is not much below 45°), we suggest that the toroids could be accreting onto the embedded cluster. For G19 and G29, the collapse is also suggested by the redshifted absorption seen in the ¹³CO (2–1) line. We infer that infall onto the embedded (proto)stars must proceed with rates of  ~10^-2   M_⊙ yr^-1 and on timescales of  ~4 × 10³–10⁴ yr. The infall rates derived for G19 and G29 are two orders of magnitude greater than the accretion rates indirectly estimated from the mass loss rate of the corresponding outflows. This suggests that the material in the toroids is not infalling onto a single massive star, which is responsible for the corresponding molecular outflow, but onto a cluster of stars.