Investigations of the Class I methanol masers in NGC 4945

Abstract

We have used the Australia Telescope Compact Array (ATCA) to conduct further observations of the 36.2-GHz (4-1 → 30E) methanol transition towards the nearby active galaxy NGC 4945. These observations have led to a more accurate determination of the offset between the maser emission and the nucleus of NGC 4945 with a typical synthesized beam of 6 arcsec × 4 arcsec (108 × 72 pc). This corresponds to a factor of 4 improvement with respect to the major axis of the beam. Other transitions of methanol and lines of other molecular species were obtained alongside the 36.2-GHz methanol emission, with strong detections of HC3N (J = 4 →3) and CS (J = 1→0) presented here.We do not detect thermal methanol (5σ upper limit of 5 mJy in a 6 kms-1 channel) from the 48.4-GHz (10 →00A+) ground-state transition, nor emission from the 44.1-GHz (70 → 61A+) class I maser transition (5s upper limit of 6 mJy in a 3 kms-1 channel). We also present a comparison of the class I maser emission observed towards NGC 4945 with that from NGC 253 and towards the Galactic giant molecular cloud G 1.6-0.025.