Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, and Water and Methanol Masers in IC 342, NGC 6946 and NGC 2146

Abstract

The Survey of Water and Ammonia in Nearby galaxies (SWAN) studies atomic and molecular species across the nuclei of four star forming galaxies: NGC\,253, IC\,342, NGC\,6946, and NGC\,2146. As part of this survey, we present Karl G. Jansky Very Large Array (VLA) molecular line observations of three galaxies: IC\,342, NGC\,6946 and NGC\,2146. NGC\,253 is covered in a previous paper. These galaxies were chosen to span an order of magnitude in star formation rates and to select a variety of galaxy types. We target the metastable transitions of ammonia NH${}_3$(1,1) to (5,5), the 22\,GHz water (H${}_2$O) ($6_{16}-5_{23}$) transition, and the 36.1\,GHz methanol (CH${}_3$OH) ($4_{-1}-3_0$) transition. {We use the NH${}_3$\ metastable lines to perform thermometry of the dense molecular gas.} We show evidence for uniform heating across the central kpc of IC\,342 with two temperature components for the molecular gas, similar to NGC 253,} of 27\,K and 308\,K, and that the dense molecular gas in NGC\,2146 has a temperature $<$86 K. We identify two new water masers in IC\,342, and one new water maser in each of NGC\,6946 and NGC\,2146. The two galaxies NGC\,253 and NGC\,2146, with the most vigorous star formation, host H${}_2$O kilomasers. Lastly, we detect the first 36\,GHz CH${}_3$OH\ masers in IC\,342 and NGC\,6946. For the four external galaxies the total CH${}_3$OH\ luminosity in each galaxy suggests a correlation with galactic star formation rate, whereas the morphology of the emission is similar to that of HNCO, a weak shock tracer.

References in corpus (8)

• Updated Nearby Galaxy Catalog
• ALMA Reveals the Molecular Medium Fueling the Nearest Nuclear Starburst
• Molecular Gas Dynamics in NGC 6946: a Bar-driven Nuclear Starburst "Caught in the Act"
• Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, Water and Methanol Masers in the Nuclear Starburst of NGC 253
• Detection of 36 GHz class I methanol maser emission towards NGCS253
• Detection of a methanol megamaser in a major-merger galaxy
• Hot Ammonia around Young O-type Stars. II. JVLA imaging of highly-excited metastable ammonia masers in W51-North
• Hot Ammonia in the Center of the Seyfert 2 galaxy NGC 3079

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• A 2-3 mm high-resolution molecular line survey towards the centre of the nearby spiral galaxy NGC 6946
• Diagnostics of a Nuclear Starburst: Water and Methanol Masers
• The magnetic fields of starburst galaxies. I. Identification and characterization of the thermal polarization in the galactic disk and outflow
• Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei
• ATLASGAL: 3-mm class I methanol masers in high-mass star formation regions
• Investigations of the Class I methanol masers in NGC 4945
• 36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?
• Astrophysical constraints on the proton-to-electron mass ratio with FAST
• Variability in extragalactic class I methanol masers: New maser components toward NGC4945 and NGC253
• A Spectral Analysis of the Centimeter Regime of Nearby Galaxies: RRLs, Excited OH, and NH${}_3$
• Evidence for Coupling of Evolved Star Atmospheres and Spiral Arms of the Milky Way
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• The universality of the relation between magnetic fields and star formation in galaxies
• Role of NH3 Binding Energy in the Early Evolution of Protostellar Cores
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