Survey of Water and Ammonia in Nearby galaxies (SWAN): Resolved Ammonia Thermometry, Water and Methanol Masers in the Nuclear Starburst of NGC 253

Abstract

We present Karl G Jansky Very Large Array molecular line observations of the nearby starburst galaxy NGC 253, from SWAN: "Survey of Water and Ammonia in Nearby galaxies". SWAN is a molecular line survey at centimeter wavelengths designed to reveal the physical conditions of star forming gas over a range of star forming galaxies. NGC 253 has been observed in four 1GHz bands from 21 to 36 GHz at 6" ($\sim 100$pc) spatial and 3.5 km s${}^{-1}$ spectral resolution. In total we detect 19 transitions from seven molecular and atomic species. We have targeted the metastable inversion transitions of ammonia (NH${}_3$) from (1,1) to (5,5) and the (9,9) line, the 22.2 GHz water (H${}_2$O) ($6_{16}-5_{23}$) maser, and the 36.1 GHz methanol (CH${}_3$OH) ($4_{-1}-3_0$) maser. Utilizing NH${}_3$ as a thermometer, we present evidence for uniform heating over the central kpc of NGC 253. The molecular gas is best described by a two kinetic temperature model with a warm 130K and a cooler 57K component. A comparison of these observations with previous ALMA results suggests that the molecular gas is not heated in photon dominated regions or shocks. It is possible that the gas is heated by turbulence or cosmic rays. In the galaxy center we find evidence for NH${}_3$(3,3) masers. Furthermore we present velocities and luminosities of three water maser features related to the nuclear starburst. We partially resolve CH${}_3$OH masers seen at the edges of the bright molecular emission, which coincides with expanding molecular superbubbles. This suggests that the masers are pumped by weak shocks in the bubble surfaces.

Accepted for publication in the Astrophysical Journal

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• Evidence of a pure starburst nature of the nuclear region of NGC 253
• Detection of 36 GHz class I methanol maser emission towards NGCS253
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Cited by in corpus (22)

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• Online Database of Class I Methanol Masers
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• The Morpho-Kinematic Architecture of Super Star Clusters in the Center of NGC253
• Class I methanol masers in NGC253: Alcohol at the end of the bar
• Diverse nuclear star-forming activities in the heart of NGC 253 resolved with ten-pc scale ALMA images
• Methanol masers in NGC 253 with ALCHEMI
• The Molecular ISM in the Super Star Clusters of the Starburst NGC 253
• The galaxy-wide stellar initial mass function in the presence of cluster-to-cluster IMF variations
• Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei
• Towards a More Complex Understanding of Natal Super Star Clusters with Multiwavelength Observations
• 36 GHz methanol lines from nearby galaxies: maser or quasi-thermal emission?
• An ALCHEMI inspection of sulphur-bearing species towards the central molecular zone of NGC 253
• 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${}_3$
• Complex Organic Molecules towards the central molecular zone of NGC 253
• Discovery of a giant molecular loop in the central region of NGC 253
• Evidence for Coupling of Evolved Star Atmospheres and Spiral Arms of the Milky Way
• The Dust Polarisation and Magnetic Field Structure in the Centre of NGC253 with ALMA
• Clustered Star Formation in the center of NGC 253 Contributes to Driving the Ionized Nuclear Wind
• Broadband VLA Spectral Line Survey of a Sample of Ionized Jet Candidates