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 (0.01 pc R ef f 0.1 pc) 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, -2derived 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 (9 − 8) 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.

CLOVER: Convnet Line-fitting Of Velocities in Emission-line Regions

“…CLOVER's two-component spectral classifications and kinematics predictions can be used to improve existing analyses that neglect the presence of multiple velocity components. For instance, many virial stability analyses of star-forming structures rely on velocity dispersions measured from models that assume a single velocity component along the line of sight (e.g., Keown et al 2017;Kirk et al 2017;Chen et al 2019a;Kerr et al 2019). When multiple velocity components are present along the line of sight, however, models assuming a single velocity component typically fit the observed spectrum with a much wider velocity dispersion than would be obtained by using a model with multiple velocity components.…”

KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE): Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds

“…Due to the hyperfine structure of NH 3 (1,1) emission, each hyperfine group would be detected as a distinct structure in a 3D dendrogram extraction of the KEYSTONE spectral cubes. To "remove" the hyperfine structures of NH 3 (1,1), some authors have created a single-Gaussian cube from the line width, peak brightness temperature, and centroid velocity measured from the NH 3 (1,1) emission (e.g., Friesen et al 2017;Keown et al 2017). Such a single-Gaussian cube attempts to represent how the ammonia emission would appear without hyperfine splitting.…”

“…The combination of dense gas kinematics and temperatures with continuum observations provides a way to measure the virial stability of dense cores and filaments (e.g., Friesen et al 2016;Kirk et al 2017;Keown et al 2017), the dissipation of turbulence from clouds and filaments to cores ("transition to coherence," Pineda et al 2010;Chen et al 2019a), and the flow of gas along or onto filaments (e.g., Schneider et al 2010a;Kirk et al 2013a;Friesen et al 2013;Henshaw et al 2013). Such measurements can also be used to determine if dense structures associated with filament intersections are susceptible to gravitational collapse.…”

“…Recent large surveys have set out to investigate the connection between dense gas kinematics and star formation by observing ammonia emission throughout different regions of the Galaxy. The Green Bank Ammonia Survey (GAS) mapped NH 3 emission throughout the nearby Gould Belt molecular clouds (d < 500 pc) where A v > 7 (e.g., Friesen et al 2017;Kirk et al 2017;Keown et al 2017;Redaelli et al 2017;Kerr et al 2019;Chen et al 2019a). The Galactic plane, which typically excludes nearby (< 3 kpc) GMCs, has been mapped in ammonia by the Radio Ammonia Mid-Plane Survey (RAMPS; covering 10 • < l < 40 • , −0.5 • < b < +0.5 • ; Hogge et al 2018) and the H 2 O Southern Galactic Plane Survey (HOPS; covering −70 • > l > 30 • , −0.5 • < b < +0.5 • ; Purcell et al 2012).…”

Searching for further evidence for cloud–cloud collisions in L1188

“…14. Figure 14a shows that most of the derived kinetic temperatures lie in the range of 13-23 K with a median value of 18 K. These values are slightly higher than those (∼10 K) obtained in other nearby dark clouds (e.g., Benson & Myers 1989;Friesen et al 2017;Keown et al 2017), but they are much lower than in OMC-1, parts of which are likely heated by radiation from the Trapezium Cluster (Friesen et al 2017;Tang et al 2018). Although the pixels at the edges have higher kinetic temperature of >25 K, they have large uncertainties (see Fig.…”