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 − 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.

Recent progress with observations and models to characterize the magnetic fields from star-forming cores to protostellar disks

“…Other clear cases of disks around massive stars, that appear to be a scaled up version of the ones around low-mass stars, are GGD MM1 (Girart et al, 2018;Añez-López et al, 2020b), G11.92-0.61 MM1 (Ilee et al, 2018), and G17.64 + 0.16 (Maud et al, 2019), with very massive (2-5 M ⊙ ), dense, and hot (≳400 K) disks. However, there are many cases reported in the literature where Keplerian velocity patterns can be fitted toward disk-like structures, which can extend from few hundreds to a thousand au (Sánchez-Monge et al, 2013;Johnston et al, 2015;Beuther et al, 2017;Cesaroni et al, 2017;Girart et al, 2017;Tanaka et al, 2020;Williams et al, 2022). In most cases, a detailed measurement of the gas temperature and surface density is needed to check the stability of such structures.…”

Could kilomasers pinpoint supermassive stars?

“…The disc's mass is about 4 M with a radius of 1600 au around a massive (7 M ) YSO (Cesaroni 2005). The most common value of radius of the disc is 500 au and some values are as high as 20,000 au 2 (see also Ilee et al 2018;Sanna et al 2021;Williams et al 2022). Taking all the above arguments into consideration we simulated accretion discs with the inner and outer radius of 𝑅 in = 10 au and 𝑅 out = 500 au or 1000 au.…”

Disk and Envelope Streamers of the GGD 27-MM1 Massive Protostar

“…Because of their typically shorter timescales, larger distances, and large obscuration, the properties of the disks around massive stars, as well as their evolution, are less known. There are many large, ∼1000 au, disk-like structures with clear velocities gradients (e.g., Sánchez-Monge et al 2013;Cesaroni et al 2017;Beuther et al 2017;Tanaka et al 2020;Williams et al 2022). Smaller disks are, however, more difficult to find (e.g., Ilee et al 2018;Maud et al 2019), but they are usually very massive (2-5 M ☉ ) and hot (400 K).…”