A survey of the 6.7 GHz methanol maser emission from IRAS sources

Abstract

We report the first results of a search for 6.7 GHz methanol masers in the direction of 1399 IRAS objects north of declination −20 • with the flux densities greater than 100 Jy at 60 µm and the flux density ratio F 60 /F 25 > 1. Observations were made with the sensitivity of 1.7 Jy and the velocity resolution of 0.04 km s −1 using the 32-m Toruń radio telescope. Maser emission was found in 182 sources, including 70 new detections. 32 new sources were identified with objects of radio emission associated with star-forming regions. Comparison of the present data set with other observations suggests that about 65% of methanol masers exhibit moderate or strong variations on timescales of about 4 and 8 years.

Absolute positions of 6.7-GHz methanol masers

“…This source displays multiple features at 6.7-GHz in the range from -16 to -9 km s −1 . Szymczak et al (2000) also reported 6.7-GHz emission in the velocity range from −31 to −25 km s −1 , which was not detected in our observations.…”

“…S255. The spectrum of Szymczak et al (2000) shows multiple spectral features, which are not visible in the VLA spectrum because of its poor velocity resolution. However, imaging shows two maser sites separated by 0.2 .…”

“…18556+0136. The spectrum of Szymczak et al (2000) shows multiple spectral features. However, in this study we found only a single feature.…”

“…The masers are widespread in the Galaxy and more than 550 sources have been detected to date, including the compilations of Xu et al (2003), Malyshev & Sobolev (2003), and Pestalozzi et al (2005), and the searches of Caswell et al (1995a), Caswell (1996aCaswell ( , 1996b, MacLeod et al (1998), Szymczak et al (2000), Pandian et al (2007), Ellingsen (2007), and Xu et al (2008).…”

Recent southern maser surveys

“…The series of Hartebeesthoek surveys (starting with MacLeod, Gaylard, Nicholson (1992) and continuing to MacLeod, van der Walt, North et al (1998)) primarily chose IRAS targets in the southern sky, and its detections usefully included some at Galactic latitudes too large to have been detected in typical blind surveys that are normally confined close to the Galactic plane; interestingly, it was also valuable in revealing the rather limited value of IRAS as a maser site predictor. From Torun, there was a similar search of IRAS sources in the northern sky (Szymczak, Hyrnek, Kus 2000). From Parkes there was a search of several hundred OH maser targets, with high success rate further demonstating the clear association of the two maser species, and providing the first extensive atlas of spectra with high sensitivity (Caswell, Vaile, Ellingsen et al 1995a).…”