2019ApJ...876..108D

We use NH₃ inversion transitions to trace the dense gas in the NGC 1333 region of the Perseus molecular cloud. NH₃ (1, 1) and NH₃ (2, 2) maps covering an area of 102 square arcminutes at an angular resolution of ∼3.''7 are produced by combining Very Large Array interferometric observations with Green Bank Telescope single-dish maps. The combined maps have a spectral resolution of 0.14 km s^–1 and a sensitivity of 4 mJy/beam. We produce integrated intensity maps, peak intensity maps, and dispersion maps of NH₃ (1, 1) and NH₃ (2, 2) and a line-of-sight velocity map of NH₃ (1, 1). These are used to derive the optical depth for the NH₃ (1, 1) main component, the excitation temperature of NH₃ (1, 1), and the rotational temperature, kinetic temperature, and column density of NH₃ over the mapped area. We compare these observations with the CARMA J = 1-0 observations of N₂H⁺ and H¹³CO⁺ and conclude that they all trace the same material in these dense star-forming regions. From the NH₃ (1, 1) velocity map, we find that a velocity gradient ridge extends in an arc across the entire southern part of NGC 1333. We propose that a large-scale turbulent cell is colliding with the cloud, which could result in the formation of a layer of compressed gas. This region along the velocity gradient ridge is dotted with Class 0/I young stellar objects, which could have formed from local overdensities in the compressed gas leading to gravitational instabilities. The NH₃ (1, 1) velocity dispersion map also has relatively high values along this region, thereby substantiating the shock layer argument.