6.7 GHz methanol maser survey toward GLIMPSE point sources and BGPS 1.1 mm dust clumps

¹ Purple Mountain Observatory, Chinese Academy of Sciences, 210008 Nanjing, PR China
e-mail: yansun@pmo.ac.cn
² Graduate University of the Chinese Academy of Sciences, 19A Yuquan road, Shijingshan District, 100049 Beijing, PR China
³ Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Beijing 100049, PR China
⁴ Shanghai Astronomical Observatory, Chinese Academy of Sciences, 200030 Shanghai, PR China
⁵ Max-Planck-Institut für Radioastronomie, auf dem Hügel 69, 53121 Bonn, Germany
⁶ Astronomy Department, Faculty of Science, King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
⁷ School of Astronomy and Space Science, Nanjing University, 210093 Nanjing, PR China

Received: 13 November 2013
Accepted: 24 January 2014

Abstract

We present the results of a 6.7 GHz methanol maser survey from the Effelsberg 100 m radio telescope. A sample of 404 sources from the Bolocam Galactic Plane Survey (BGPS) 1.1 mm dust clump survey that met specific Galactic Legacy Infrared Mid-Plane Survey Extraodinaire (GLIMPSE) point-source color criteria was selected and 318 of these were observed. The new observations resulted in the detection of 29 methanol masers, including 12 new ones. Together with the additional 74 detections from the literature, this means that a total of 103 methanol masers are coincident with 1.1 mm dust clumps, yielding an overall detection rate of 26%. A comparison of the properties of a 1.1 mm dust clump and a 6.7 GHz methanol maser indicates that methanol masers with a higher flux density and/or luminosity are generally associated with more massive but less dense 1.1 mm dust clumps. The overall detection rate of 26% appears to vary as a function of the derived H₂ column density of the associated 1.1 mm dust clump. The methanol masers were primarily detected toward the brighter and more massive 1.1 mm dust clumps. A subsample of 194 sources that overlapped sources with observations of the 95 GHz methanol line was investigated in more detail for the properties of 1.1 mm dust clumps. The statistical analysis reveals that 1.1 mm dust clumps with both class I and II counterparts have much higher mean and median values of mass, column density, and flux density than those with only class I or II counterparts. Based on our much larger sample, we slightly revise the boundary defined previously for selecting BGPS sources associated with a class II methanol maser, wherein ~80% of expected class II methanol masers will be detected with a detection rate in the range of 40–50%.