The Green Bank Ammonia Survey: Observations of Hierarchical Dense Gas Structures in Cepheus-L1251

Abstract

We use Green Bank Ammonia Survey observations of NH 3 (1, 1) and (2, 2) emission with 32″ FWHM resolution from a ∼10 pc 2 portion of the Cepheus-L1251 molecular cloud to identify hierarchical dense gas structures. Our dendrogram analysis of the NH 3 data results in 22 top-level structures, which reside within 13 lower-level parent structures. The structures are compact and are spatially correlated with the highest H 2 column density portions of the cloud. We also compare the ammonia data to a catalog of dense cores identified by higher-resolution (18.″2 FWHM) Herschel Space Observatory observations of dust continuum emission from Cepheus-L1251. Maps of kinetic gas temperature, velocity dispersion, and NH 3 column density, derived from detailed modeling of the NH 3 data, are used to investigate the stability and chemistry of the ammonia-identified and Herschel -identified structures. We show that the dust and dense gas in the structures have similar temperatures, with median T dust and T K measurements of 11.7 ± 1.1 K and 10.3 ± 2.0 K, respectively. Based on a virial analysis, we find that the ammonia-identified structures are gravitationally dominated, yet may be in or near a state of virial equilibrium. Meanwhile, the majority of the Herschel -identified dense cores appear to be not bound by their own gravity and instead confined by external pressure. CCS (2 0 − 1 0 ) and HC 5 N emission from the region reveal broader line widths and centroid velocity offsets when compared to the NH 3 (1, 1) emission in some cases, likely due to these carbon-based molecules tracing the turbulent outer layers of the dense cores.