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 Karl G. Jansky Very (VLA), we observed 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 ALMA observations reveal a velocity gradient across millimetre core MM1, oriented perpendicular previously known bipolar molecular outflow, which is consistently traced by 20 lines of 8 species range excitation temperatures, including complex organic molecules (COMs). Kinematic modelling shows data are well described models that include disc in Keplerian rotation infall, an enclosed mass 40–70 M⊙ (within 2000 outer radius) for inclination angle i = 40○, 5.4–7.2 attributed disc. new VLA show 6.7 GHz Class II methanol masers associated MM1 form partial ellipse, consistent inclined ring, thermal gas. The disc-to-star ratio suggests likely be unstable may fragmenting into as-yet-undetected low-mass stellar companions. Modelling centimetre–millimetre spectral energy distribution continuum emission dominated dust, whilst free–free component, interpreted as hypercompact H ii region, required explain ∼5 emission. high derived source moderate bolometric luminosity (∼104 L⊙) feed unresolved high-mass binary system.