A subarcsecond study of the hot molecular core in G023.01−00.41 ^⋆,⋆⋆

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: asanna@mpifr-bonn.mpg.de
² INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA
⁴ INAF-IFSI, via Fosso del Cavaliere 100, 00133 Roma, Italy
⁵ Stratospheric Observatory for Infrared Astronomy-USRA, NASA Ames Research Center, MS.N232-12, Moffet Field CA 94035, USA

Received: 25 November 2013
Accepted: 13 February 2014

Abstract

Context. Searching for disk-outflow systems in massive star-forming regions is a key to assessing the main physical processes in the recipe of massive star formation.

Aims. We have selected a hot molecular core (HMC) in the high-mass star-forming region G023.01−00.41, where VLBI multi-epoch observations of water and methanol masers have suggested the existence of rotation and expansion within 2000 AU of its center. Our purpose is to image the thermal line and continuum emission at millimeter wavelengths to establish the physical parameters and velocity field of the gas in the region.

Methods. We performed SMA observations at 1.3 mm with both the most extended and compact array configurations, providing subarcsecond and high sensitivity maps of various molecular lines, including both hot-core and outflow tracers. We also reconstructed the spectral energy distribution of the region from millimeter to near infrared wavelengths, using the Herschel/Hi-GAL maps, as well as archival data.

Results. From the spectral energy distribution, we derive a bolometric luminosity of ~4 × 10⁴ L_⊙. Our interferometric observations reveal that the distribution of dense gas and dust in the HMC is significantly flattened and extends up to a radius of 8000 AU from the center of radio continuum and maser emission in the region. The equatorial plane of this HMC is strictly perpendicular to the elongation of the collimated bipolar outflow, as imaged on scales of ~0.1–0.5 pc in the main CO isotopomers, as well as in the SiO(5–4) line. In the innermost HMC regions (≲1000 AU), the velocity field traced by the CH₃CN (12_K − 11_K) line emission shows that molecular gas is both expanding along the outflow direction following a Hubble law and rotating about the outflow axis, in agreement with the (3D) velocity field traced by methanol masers. The velocity field associated with rotation indicates a dynamical mass of ~19 M_⊙ at the center of the core. The latter is likely to be concentrated in a single O9.5 ZAMS star, consistent with the estimated bolometric luminosity of G023.01−00.41. The physical properties of the CO (2–1) outflow emission, such as its momentum rate 6 × 10^-3 M_⊙ km s^-1 yr^-1 and its outflow rate 2 × 10^-4 M_⊙ yr^-1, support our estimates of the luminosity (and mass) of the embedded young stellar object.