A 12.2 GHz Methanol Maser Survey toward the 6.7 GHz Counterparts Associated with/without UC H ii Regions

Abstract

We report a new survey of the 12.2 GHz Class II methanol masers toward a sample of 367 sources with the 6.7 GHz methanol masers conducted with the Shanghai 65 m Tianma Radio Telescope. This sample has been previously made with observations of the radio continuum emission of UC H ii regions by the VLA. A total of 176 sources were detected with the 12.2 GHz methanol maser, with a detection rate of 48%, including 8 new detections. A lower detection rate (<10%) was determined toward the sources in the Galactic longitude ranges of 60°–180°, revealing that the physical environments from those sources in the Local arm or the tails of Galactic arms do not easily excite the 12.2 GHz masers. In addition, two detections of highly excited-state OH masers at the 13.4 GHz transition were made, one of which is a new detection. Compared to previous surveys, one-third of the detected 12.2 GHz masers show considerable flux variations, implying the possible changes of their physical environments associated with variable radiation fields from their host high-mass young stellar objects. A positive log–log correlation is found between the luminosities of the 6.7 and 12.2 GHz masers in our observed sample, suggesting that both the transition masers have similar excitation conditions. The statistical analysis for the relationships between the methanol maser luminosity and UC H ii region spatial size indicates that the maser luminosities of both the 6.7 and 12.2 GHz transitions have a decreasing trend with the spatial sizes of the associated UC H ii regions, indicating that the Class II methanol masers might fade away with the H ii region evolution.

New Methanol Maser Transitions and Maser Variability Identified from an Accretion Burst Source G358.93-0.03

“…It is also noted that the 12.18 GHz maser emission is generally stronger than the 6.67 GHz on the same observing dates (see Figure 4). Usually, the 6.67 GHz maser emission is stronger than the 12.18 GHz in almost all of the sources with both maser transition detections (Breen et al 2012;Song et al 2022). But our observations present a reversal detection in G358, suggesting that the physical conditions at the time of the accretion burst event in G358 might significantly change with respect to those expected in MSFRs without the accretion bursts.…”

Maser Activity of Organic Molecules toward Sgr B2(N)

“…An empirical taxonomy based on pumping mechanisms classifies molecular masers into two categories (Batrla et al 1987;Cyganowski et al 2009); H 2 O and Class I CH 3 OH masers are most often excited via collisions and tend to reside in shocked material associated with outflows and expanding H II regions (e.g., Baudry et al 1974;Elitzur & Fuqua 1989;Voronkov et al 2014;Towner et al 2017), while OH and Class II CH 3 OH masers are excited via radiation and are generally close to young stellar objects and luminous infrared sources (e.g., Sobolev & Deguchi 1994;Sobolev et al 1997;Cragg et al 2002Cragg et al , 2005. The most extensively studied Class I CH 3 OH masers include the 4 −1 − 3 0 E transition at 36 GHz and the 7 0 − 6 1 A transition at 44 GHz, while Class II CH 3 OH masers include the 5 1 − 6 0 A transition at 6.7 GHz and the 2 0 − 3 −1 E transition at 12.2 GHz (e.g., Voronkov et al 2014;Song et al 2022).…”

A Multitransition Methanol Survey toward a Large Sample of High-mass Star-forming Regions

“…Detectable CH 3 OH emissions are included in both maser and thermal lines. Recently, a wealth of maser observations (e.g., Yang et al , 2020Yang et al , 2019Song et al 2022) and maser surveys (e.g., the Methanol Multi-beam Survey; Breen et al 2012aBreen et al , 2012bBreen et al , 2014Breen et al , 2016Breen et al , 2018Cunningham et al 2018) have been conducted. Similarly, many observational studies have been carried out for CH 3 OH thermal lines.…”