A survey of the Galactic plane for 6.7-GHz methanol masers -- I. l = 325 -335 ; b= - 0Formula53-0Formula53

We report the results of the first complete survey of an area of the GalacticPlane for maser emission from the 6.7-GHz transition of methanol. The surveycovers a 10.6-square-degree region of the Galactic Plane in the longitude range325-335 degrees and latitude range -0.53-0.53 degrees. The survey is sensitiveto masers with a peak flux density greater than approximately 2.6 Jy. Theweakest maser detected has a peak flux density of 2.3 Jy and the strongest apeak flux density of 425 Jy. We detected a total of 50 distinct masers, 26 ofwhich are new detections. We show that many 6.7-GHz methanol masers are notassociated with IRAS sources, and that some are associated with sources thathave colours differing from those of a typical ultra-compact HII region(UCHII). We estimate that the number of UCHII regions in the Galaxy issignificantly more than suggested by IRAS-based estimates, possibly by morethan a factor of two.Comment: 19 pages including 4 figures, using LaTeX formatted with mn.sty, accepted for publication in MNRA