Multi-wavelength maser observations of the Extended Green Object G19.01—0.03

Abstract We report the detections of NH3(3,3) and 25 GHz and 278.3 GHz class I CH3OH maser emission associated with the outflow of the Extended Green Object G19.01–0.03 in sub-arcsecond resolution Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (VLA) observations. For masers associated with the outer outflow lobes (> 12.5 ″ from the central massive young stellar object; MYSO), the spatial distribution of the NH3(3,3) masers is statistically indistinguishable from that of previously known 44 GHz Class I CH3OH masers, strengthening the connection of NH3(3,3) masers to outflow shocks. In sub-arcsecond resolution VLA observations, we resolve the 6.7 GHz Class II CH3OH maser emission towards the MYSO into a partial, inclined ring, with a velocity gradient consistent with the rotationally supported circumstellar disc traced by thermal gas emission.


Introduction
Masers are well-established tracers of massive young stellar objects (MYSOs) and their outflows, with high-resolution Karl G. Jansky Very Large Array (VLA) and Atacama Large Millimeter/(sub)millimeter Array (ALMA) observations ongoing over the past decade continuing to lead to the identification of new maser lines in these environments.In this proceeding, we summarise our recent sub-arcsecond resolution ALMA and VLA observations of maser emission towards the Extended Green Object (EGO) G19.01-0.03,an MYSO that drives a well-collimated bipolar outflow (Williams et al. 2022(Williams et al. , 2023)).

Outflow-tracing maser emission, and a 6.7 GHz Class II methanol maser ring
The CH 3 OH(9 −1,9 − 8 0,8 ) line at 278.3 GHz is known to exhibit maser behaviour (e.g.Yanagida et al. 2014).Our ALMA peak intensity map of this line (Figure 1a) shows it generally traces the morphology of the bipolar outflow driven by the central MYSO  (previously observed in 12 CO, SiO and HCO + by Cyganowski et al. 2011).We classify the brightest 278.3 GHz CH 3 OH emission as a candidate maser, due to (i) its narrow spectral profile, (ii) its brightness temperature being an order of magnitude higher than that of thermal CH 3 OH lines in our spectral tuning, and (iii) its coincidence, both spatially and kinematically, with known 44 GHz Class I CH 3 OH masers (Cyganowski et al. 2009) and newly identified NH 3 (3,3) masers.NH 3 (3,3) is known to exhibit maser behaviour thought to arise due to outflow-induced shocks (e.g.Brogan et al. 2011).With our ∼ 0.5 resolution VLA observations, we detect 50 NH 3 (3,3) maser emission spots to the > 5σ level in the outflow (Figure 1a).These spots are coincident spatially and kinematically with the outflow-tracing 278.3 GHz CH 3 OH emission.At large angular separation from the MYSO (> 12.5 ), their spatial distribution is statistically indistinguishable from that of known 44 GHz Class I CH 3 OH masers (Figure 1b).
Multi-Wavelength Masers Towards G19.01−0.03263 With VLA 2.8 resolution observations, Cyganowski et al. (2009) detected 6.7 GHz Class II CH 3 OH maser emission towards the central MYSO.With our new ∼ 0.6 resolution VLA observations, the maser spot distribution exhibits a partial ellipse, consistent with an inclined ring (Figure 1c).The strongest maser emission is blue-shifted with respect to the systemic velocity of the MYSO (∼60 km s −1 ; Cyganowski et al. 2011), and the maser velocities follow that of the Keplerian circumstellar disc traced by thermal gas emission (Williams et al. 2022).
G. M.Williams et al.

Figure 1 .
Figure 1.(a) ALMA peak intensity map of the CH3OH(9−1,9 − 80,8) line at 278.3 GHz towards G19.01−0.03.The white circle marks the position of peak emission.ALMA 1.05 mm continuum contours are shown in black towards the MYSO at 64, 256 and 600σ.The orange cross marks the intensity-weighted 6.7 GHz Class II CH3OH maser position (as in Fig.1c).Blue pluses denote new NH3(3,3) maser spots, and pink crosses denote 44 GHz Class I CH3OH masers (Cyganowski et al. 2009).The green diamond marks the 25 GHz Class I CH3OH maser.(b) Histogram of the angular separation of the NH3(3,3) and 44 GHz Class I CH3OH maser spots (blue and pink respectively; as in Fig.1a) from the MYSO's ALMA 1.05 mm continuum peak (Williams et al. 2023).(c) Fitted 6.7 GHz Class II CH3OH maser positions, coloured by velocity, overplotted on the VLA 5.01 cm continuum (adapted from Williams et al. 2022).The black cross and yellow and cyan pluses show the 1.05 mm, 5.01 cm and 1.21 cm continuum peak positions respectively.