ALMA observations of the Extended Green Object G19.01-0.03 - I. A Keplerian disc in a massive protostellar system
Abstract
Using the Atacama Large Millimetre/submillimeter Array (ALMA) and the Karl G. Jansky Very Large Array (VLA), we observed the Extended Green Object (EGO) G19.01-0.03 with sub-arcsec resolution from 1.05 mm to 5.01 cm wavelengths. Our ~0.4 arcsec ~ 1600 AU angular resolution ALMA observations reveal a velocity gradient across the millimetre core MM1, oriented perpendicular to the previously known bipolar molecular outflow, which is consistently traced by 20 lines of 8 molecular species with a range of excitation temperatures, including complex organic molecules (COMs). Kinematic modelling shows the data are well described by models that include a disc in Keplerian rotation and infall, with an enclosed mass of 40-70 M⊙ (within a 2000 AU outer radius) for a disc inclination angle of i = 40○, of which 5.4-7.2 M⊙ is attributed to the disc. Our new VLA observations show that the 6.7 GHz Class II methanol masers associated with MM1 form a partial ellipse, consistent with an inclined ring, with a velocity gradient consistent with that of the thermal gas. The disc-to-star mass ratio suggests the disc is likely to be unstable and may be fragmenting into as-yet-undetected low-mass stellar companions. Modelling the centimetre-millimetre spectral energy distribution of MM1 shows the ALMA 1.05 mm continuum emission is dominated by dust, whilst a free-free component, interpreted as a hypercompact H II region, is required to explain the VLA ~5 cm emission. The high enclosed mass derived for a source with a moderate bolometric luminosity (~104 L⊙) suggests that the MM1 disc may feed an unresolved high-mass binary system.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- January 2022
- DOI:
- 10.1093/mnras/stab2973
- arXiv:
- arXiv:2110.06262
- Bibcode:
- 2022MNRAS.509..748W
- Keywords:
-
- masers;
- techniques: interferometric;
- stars: formation;
- stars: individual: G19.01-0.03;
- stars: massive;
- stars: protostars;
- Astrophysics - Astrophysics of Galaxies;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 15 pages, 8 figures, 5 tables, Accepted for publication in MNRAS