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The central few 100 pc of galaxies often contain large amounts of moleculargas. The chemical and physical properties of these extragalactic star formationregions differ from those in galactic disks, but are poorly constrained. Thisstudy aims to develop a better knowledge of the spatial distribution andkinetic temperature of the dense neutral gas associated with the nuclearregions of three prototypical spiral galaxies, NGC253, IC342, and Maffei2. VLACnD and D configuration measurements have been made of three ammonia (NH3)inversion transitions. The (J,K)=(1,1) and (2,2) transitions of NH3 were imagedtoward IC342 and Maffei2. The (3,3) transition was imaged toward NGC253. Theentire flux obtained from single-antenna measurements is recovered for allthree galaxies observed. Derived lower limits to the kinetic temperaturesdetermined for the giant molecular clouds in the centers of these galaxies arebetween 25 and 50K. There is good agreement between the distributions of NH3and other H2 tracers, such as rare CO isotopologues or HCN, suggesting that NH3is representative of the distribution of dense gas. The "Western Peak" in IC342is seen in the (6,6) line but not in lower transitions, suggesting maseremission in the (6,6) transition.

Dense Gas in Nearby Galaxies: XVII. The Distribution of Ammonia in NGC253, Maffei2 and IC342