Thermal Starless Ammonia Core Surrounded by CCS in the Orion A Cloud

Abstract

We imaged two starless molecular cloud cores, TUKH083 and TUKH122, in the Orion A giant molecular cloud in the CCS and ammonia (NH${}_3$) emission with the Very Large Array. TUKH122 contains one NH${}_3$ core "TUKH122-n," which is elongated and has a smooth oval boundary. Where observed, the CCS emission surrounds the NH${}_3$ core. This configuration resembles that of the N${}_2$H${}^{+}$ and CCS distribution in the Taurus starless core L1544, a well-studied example of a dense prestellar core exhibiting infall motions. The linewidth of TUKH122-n is narrow (0.20 km s${}^{-1}$) in the NH${}_3$ emission line and therefore dominated by thermal motions. The smooth oval shape of the core boundary and narrow linewidth in NH${}_3$ seem to imply that TUKH122-n is dynamically relaxed and quiescent. TUKH122-n is similar to L1544 in the kinetic temperature (10 K), linear size (0.03 pc), and virial mass ($\sim$ 2 $M_{\odot }$). Our results strongly suggest that TUKH122-n is on the verge of star formation. TUKH122-n is embedded in the 0.2 pc massive (virial mass $\sim$ 30 $M_{\odot }$) turbulent parent core, while the L1544 NH${}_3$ core is embedded in the 0.2 pc less-massive (virial mass $\sim$ 10 $M_{\odot }$) thermal parent core. TUKH083 shows complicated distribution in NH${}_3$, but was not detected in CCS. The CCS emission toward TUKH083 appears to be extended, and is resolved out in our interferometric observations.

38 pages, 13 figures, ApJ, in press

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• An Ammonia Spectral Map of the L1495-B218 Filaments in the Taurus Molecular Cloud: II CCS & HC${}_7$N Chemistry and Three Modes of Star Formation in the Filaments
• ALMA ACA and Nobeyama observations of two Orion cores in deuterated molecular lines
• Chemical evolution of the HC3N and N2H+ molecules in dense cores of the Vela C giant molecular cloud complex
• An ALCHEMI inspection of sulphur-bearing species towards the central molecular zone of NGC 253
• Detection of a turbulent gas component associated with a starless core with subthermal turbulence in the Orion A cloud
• Magnetic field measurement in TMC-1C using 22.3 GHz CCS Zeeman splitting
• Studying the chemical and kinematical structures of dense cores TMC-1C, L1544, and TMC-1 in the Taurus molecular cloud using the CCS and NH3 observations
• The TMRT K Band Observations towards 26 Infrared Dark Clouds: NH${}_3$, CCS, and HC${}_3$N