SiO collimated outflows driven by high-mass YSOs in G24.78+0.08

¹ INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
e-mail: codella@arcetri.astro.it
² UJF – Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
³ IRAM, 300 rue de la Piscine, 38406 Saint Martin d’Hères, France
⁴ Harward-Smithsonian Center for Astrophysics, 60 Garden Street, MA 02138 Cambridge, USA

Received: 26 June 2012
Accepted: 20 November 2012

Abstract

Context. The region G24.78+0.08, which is associated with a cluster of high-mass young stellar objects in different evolutionary stages, is one of the best laboratories to investigate massive star formation.

Aims. We aim to image the molecular outflows towards G24.78+0.08 at high-angular resolution using SiO emission, which is considered the classical tracer of protostellar jets. In this way we study the mass loss process in which we previously detected a hypercompact ionised region, as well as rotation and infall signatures.

Methods. We performed SiO observations with the VLA interferometer in the J = 1–0 v = 0 transition and with the SMA array in the 5–4 transition. A complementary IRAM 30-m single-dish survey in the (2–1), (3–2), (5–4), and (6–5) SiO lines was also carried out.

Results. Two collimated SiO high-velocity (up to 25 km s^-1 w.r.t. the systemic velocity) outflows driven by the A2 and C millimeter continuum massive cores have been imaged. On the other hand, we detected no SiO outflow driven by the young stellar objects in more evolved evolutionary phases that are associated with ultracompact (B) or hypercompact (A1) Hii regions. The A2 outflow has also been traced using H₂S. The LVG analysis of the SiO emission reveals high-density gas (10³–10⁴ cm^-3), with well constrained SiO column densities (0.5−1 × 10¹⁵ cm^-2). The driving source of the A2 outflow is associated with typical hot core tracers such as CH₃OCHO (methyl formate), C₂H₃CN (vinyl cyanide), HCC¹³CN (cyanoacetilene), and (CH₃)₂CO (acetone).

Conclusions. The driving source of the main SiO outflow in G24 has an estimated luminosity of a few 10⁴ L_⊙ (typical of a late O-type star) and is embedded in the 1.3 mm continuum core A2, which in turn is located at the centre of a hot core that rotates on a plane perpendicular to the outflow main axis. The present SiO images support a scenario similar to the low-mass case for massive star formation, where jets that are clearly traced by SiO emission, create outflows of swept-up ambient gas usually traced by CO.