A 6.7 GHz Methanol Maser Survey. II. Low Galactic Latitudes

We report the results of our systematic survey for Galactic 6.7 GHz Class II CH3OH maser emission toward a sample of young stellar objects. The survey was conducted with the Shanghai Tianma Radio Telescope (TMRT). The sample consists of 3348 sources selected from the all-sky Wide-field Infrared Survey Explorer (WISE) point-source catalog. We discussed the selection criteria in detail and the detection results of those at high Galactic latitudes (i.e., vertical bar b vertical bar > 2 degrees) in a previous paper (Yang et al. 2017). Here, we present the results from the survey of those at low Galactic latitudes, i.e., vertical bar b broken vertical bar < 2 degrees. Of 1875 selected WISE point sources, 291 positions that were actually associated with 224 sources that were detected with CH3OH maser emission. Among them, 32 are newly detected. A majority of the newly detected sources are associated with bright WISE sources. The majority of the detected sources (209/224. = 93.3%) are quite close to the Galactic Plane (vertical bar b vertical bar < 1 degrees)and lie on the inner spiral arms with positive local standard of rest velocities. The detection rate and the color-color distribution of our detection are all matched with our anticipation. Combining with detections from previous surveys, we compile a catalog of 1085 sources with 6.7 GHz CH3OH maser emission in our Galaxy.