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 ($4_{-1}\to 3_0$E) 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 synthesised beam of $6^{\prime \prime }\times 4^{\prime \prime }$ ($108\times 72$ 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 HC${}_3$N (J = $4\to 3$) and CS (J = $1\to 0$) presented here. We do not detect thermal methanol (5$\sigma$ upper limit of 5 mJy in a 6 km s${}^{-1}$ channel) from the 48.4-GHz ($1_0\to 0_0$A${}^{+}$) ground-state transition, nor emission from the 44.1-GHz ($7_0\to 6_1$A${}^{+}$) class~I maser transition (5$\sigma$ upper limit of 6 mJy in a 3 km s${}^{-1}$ 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.

Accepted 2018 August 03 into MNRAS. 13 pages, 5 figures and 4 tables