Abstract
Abstract We report the detection of a new class I methanol maser candidate from the 52−41 E transition (266.8 GHz). This methanol transition has been detected toward a nearby high-mass star-forming region G352.630-1.067 (distance ∼0.7 kpc), in Submillimeter Array (SMA) observations. The new candidate transition has a similar spatial distribution as the 42−31 E (218.4 GHz) and 8−1−70 E (229.7 GHz) transitions, which are known class I maser transitions. Thermal methanol emission in this source is confined to a central hot core, while the three class I maser transitions are detected in two additional regions. These two maser-only emission regions are clearly associated with shocked gas traced by 2 μm Ks-band and thermal v = 0, J = 5−4 SiO molecular emission. In contrast to the thermal methanol emission from the hot core, the three class I maser transitions show an positive trend in the rotation diagram for the two maser regions. Large velocity gradient modeling of the 266.8, 218.4, and 229.7 GHz transitions shows that the 266.8 GHz transition can be a maser for a wide range of conditions. The intensity ratios for the three methanol transitions detected in maser regions can be reproduced under conditions that are typical for class I methanol maser sites. These facts all support the hypothesis that the detected emission from the 266.8 GHz methanol (52−41 E) transition is masing.
Highlights
Methanol maser emission is a very common phenomenon in our Galaxy (e.g., Green et al 2009; Chen et al 2014; Yang et al 2017)
Submillimeter Array (SMA) observations of the nearby high-mass star-forming regions (HMSFRs) G352.630-1.067 have detected a new class I methanol maser from the 52−41 E transition (266.8 GHz). This new class I maser shows similar emission and spectral characteristics as the two previously known maser transitions, the 42−31 E (218.4 GHz) and 8−1−70 E (229.7 GHz) lines, which were detected in the current observations
In contrast to other thermal methanol lines, which were only observed toward the hot core region, maser transitions were detected in two additional regions
Summary
Methanol maser emission is a very common phenomenon in our Galaxy (e.g., Green et al 2009; Chen et al 2014; Yang et al 2017). Class I methanol masers have a collisional source of pumping (Sobolev & Strelnitskii 1983; Cragg et al 1992), and they are commonly produced by mild shocks driven into molecular clouds by protostellar outflows from high- or low-mass stars, expanding H II regions (e.g., Voronkov et al 2010a; Chen et al 2011), expanding supernova remnants (Pihlström et al 2014), expanding envelopes of the late type stars (Nakashima et al 2015), and rapidly moving cloudlets (Voronkov et al 2010b).
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