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

<jats:title>Abstract</jats:title> <jats:p>We use Green Bank Ammonia Survey observations of NH<jats:sub>3</jats:sub> (1, 1) and (2, 2) emission with 32″ FWHM resolution from a ∼10 pc<jats:sup>2</jats:sup> portion of the Cepheus-L1251 molecular cloud to identify hierarchical dense gas structures. Our dendrogram analysis of the NH<jats:sub>3</jats:sub> data results in 22 top-level structures, which reside within 13 lower-level parent structures. The structures are compact <jats:inline-formula> <jats:tex-math> <?CDATA $(0.01\,\mathrm{pc}\lesssim {R}_{\mathrm{eff}}\lesssim 0.1\,\mathrm{pc})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa93ecieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and are spatially correlated with the highest H<jats:sub>2</jats:sub> 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) <jats:italic>Herschel Space Observatory</jats:italic> observations of dust continuum emission from Cepheus-L1251. Maps of kinetic gas temperature, velocity dispersion, and NH<jats:sub>3</jats:sub> column density, derived from detailed modeling of the NH<jats:sub>3</jats:sub> data, are used to investigate the stability and chemistry of the ammonia-identified and <jats:italic>Herschel</jats:italic>-identified structures. We show that the dust and dense gas in the structures have similar temperatures, with median <jats:italic>T</jats:italic> <jats:sub>dust</jats:sub> and <jats:italic>T</jats:italic> <jats:sub> <jats:italic>K</jats:italic> </jats:sub> 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 <jats:italic>Herschel</jats:italic>-identified dense cores appear to be not bound by their own gravity and instead confined by external pressure. CCS (2<jats:sub>0</jats:sub> − 1<jats:sub>0</jats:sub>) and HC<jats:sub>5</jats:sub>N <jats:inline-formula> <jats:tex-math> <?CDATA $(9-8)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjaa93ecieqn2.gif" xlink:type="simple" /> </jats:inline-formula> emission from the region reveal broader line widths and centroid velocity offsets when compared to the NH<jats:sub>3</jats:sub> (1, 1) emission in some cases, likely due to these carbon-based molecules tracing the turbulent outer layers of the dense cores.</jats:p>