ALMA observations of the Extended Green Object G19.01–0.03: I. A Keplerian disc in a massive protostellar system

G. M. Williams, C.J. Cyganowski, C. L. Brogan, T. R. Hunter, J. D. Ilee, P. Nazari, J.M.D. Kruijssen, Rowan Smith, I. A. Bonnell

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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 1.05mm to 5.01 cm wavelengths. Our 0•400 1600AU 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 2000AU outer radius) for a disc inclination angle of 𝑖 = 40, of which 5•4 􀀀 7•2M is attributed to the disc. Our new VLA observations show that the 6.7GHz 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 1.05mm 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.
Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Publication statusPublished - 18 Oct 2021


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