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-arcsecond resolution from 1.05 mm to 5.01 cm wavelengths. Our 0.4'' ∼ 1600 AU angular resolution ALMA observations reveal a velocity gradient across the millimetre core MM1, oriented perpendicular to the previously known bipolar molecular outflow, that 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 40-70M⊙ (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 HII 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.
Citation
Williams , G M , Cyganowski , C J , Brogan , C L , Hunter , T R , Ilee , J D , Nazari , P , Kruijssen , J M D , Smith , R J & Bonnell , I A 2022 , ' ALMA observations of the Extended Green Object G19.01-0.03 I. A Keplerian disc in a massive protostellar system ' , Monthly Notices of the Royal Astronomical Society , vol. 509 , no. 1 , pp. 748–762 . https://doi.org/10.1093/mnras/stab2973
Publication
Monthly Notices of the Royal Astronomical Society
Status
Peer reviewed
ISSN
0035-8711Type
Journal article
Description
G.M.W. acknowledges support from the Uk's Science and Technology Facilities Council (STFC) under ST/R000905/1 and ST/M001296/1. C.J.C acknowledges support from the UK's STFC under ST/M001296/1 and J.D.I. acknowledges support from the UK's STFC under ST/T000287/1. J.M.D.K gratefully acknowledges funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) through an Emmy Noether Research Group (grant number KR4801/1-1 and the DFG Schbeihilfe (grant number KR4801/2-1 as well as from the European Research Council (ERC) under the European Enion's Horizon 2020 Research and Innovation programme via the ERC starting grant MUSTANG (grant agreement number 714907)Collections
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