Observational Studies Of Class ? Methanol Masers

The methanol molecule has numerous transitions within the centimeter-and millimeter-wavelength ranges and hence provides a powerful tool for the study of star-forming regions,which makes them the focus of research in recent years.Methanol masers are divided into two categories,based on their associated star star-forming phe-nomena and pumping mechanisms.Among them,class ? methanol masers(such as at 44 GHz and 95 GHz)usually exist in the shock environments driven by the outflow.It is of great significance to the exploration of the shock environment of star formation in the region and the maser-based evolutionary sequence of high mass star formation.However,compared with the search and research of other masers in the Milky Way,the search and research of type ? methanol maser is relatively lagging,mainly because the frequency of type ? methanol maser is relatively high,and there is a lack of suitable search samples before.With the upgrade of observation equipment in recent years and the release of millimeter wave and infrared survey data of the galaxy,such as BGPS,Spitzer GLIMPSE,WISE,etc.,a large sample search for class ? methanol maser and its research To be carried out.This article mainly involves the following work:(1)Searching for 95 GHz class ? methanol masers toward a large sample of 1.1 mm BGPS source.We used the PMO-13.7m telescope to search for 95 GHz methanol masers toward 1020 Bolocam Galactic Plane Survey(BGPS)sources,leading to 213 detections.We have compared the line width of the methanol and HCO+thermal emis-sion in all of the methanol detections,and on that basis,we found that 205 of the 213 detections are very likely to be masers.This corresponds to an overall detection rate of 95 GHz methanol masers toward our BGPS sample of 20%.Of the 205 detected masers,144 are new discoveries.(2)Compiling a 95 GHz methanol masers catalog.Combining our 95 GHz methanol maser detection toward BGPS sources with those of previous 95 GHz methanol maser searches,a total of 481 95 GHz methanol masers are now known.We have compiled a catalog listing the locations and properties of all known 95 GHz methanol masers.This is the largest 95 GHz methanol maser catalog and was also the largest class ? methanol maser catalog at that time.(3)Searching for 44 GHz methanol masers toward 95 GHz methanol masers.The observations were made with the three telescopes of the Korean VLBI Network oper-ating in single-dish mode.The detection rates are 89%at 44 GHz and 77%at 95 GHz.There are 106 new discoveries at 44 GHz.Comparing the previous 95 GHz detections with new observations of the same transitions made using Purple Mountain Observatory 13.7 m radio telescope shows no clear evidence of variability.We found that the peak flux density ratio,Spk,95/Spk.44 ranges from 0.1 to 2·8,with a typical value of 0.5,and it decreases as the 44 GHz peak flux density increases.We found some class ? methanol masers in our sample could be associated with infrared dark clouds,while others are associated with HII regions,indicating that some sources occur at an early stage of high-mass star formation,while others are located toward more evolved sources.