The KEYSTONE Survey: Initial Release and Overview of Hierarchical Ammonia Structures in Galactic Giant Molecular Clouds
Abstract
Filamentary structures have been observed in continuum dust emission in both low- and high-mass star forming regions at all stages of the star formation process. Massive young stellar objects (MYSOs) and stellar clusters appear to be preferentially located at intersections of multiple filaments as revealed by dust continuum observations of these regions, suggesting that mass flow along these filaments may enable the high-density conditions necessary for MYSO formation. Observations of molecular tracers such as NH3 or N2H+ are critical to understanding the dynamics that may reveal the role that filaments have in the star-forming process. These molecules are less prone to freezing out at high densities than CO, and are optically thin at high densities. Most importantly, their hyperfine structures allow for a more convenient determination of optical depth, excitation temperatures, and kinematics of the star-forming cores. We present the initial results of the KFPA Examinations of Young STellar Object Natal Environments (KEYSTONE) survey. KEYSTONE is a GBT large project survey that has used the K-band Focal Plane Array on the Green Bank Telescope to map the first five NH3 inversion transitions in all 11 GMCs between 0.9 kpc and 3.0 kpc identified in dust continuum measurements from the Herschel OB Young Stars (HOBYS) survey. KEYSTONE has produced a complete survey of high mass star formation at distances less than 3 kpc. We have modeled the NH3 (1,1) and (2,2) maps to characterise the kinetic temperature, velocities, velocity dispersion, and column densities of each region. We have identified 856 dense gas clumps in the sample through a dendrogram analysis of the integrated NH3 (1,1) emission. Our virial analysis indicates that 63% (523/835) of the clumps with mass estimates are sufficiently massive to be gravitationally bound. We find that the fractions of these ammonia-identified clumps that are spatially coordinated with filaments to be similar to other nearby star-forming regions (between 0.35 to 1.00). Several of the regions show "hubs" or "ridges" of dense gas that have much higher masses and lower virial parameters than other clumps in their respective cloud. These are located within a single filament or at intersections of multiple filaments, and are often associated with multiple protostars and H2O maser emission, and we suspect that these hubs may be the site of future cluster formation. The KEYSTONE dataset is expected to be a rich source of information on dense gas kinematics for further characterisation of massive star formation.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23531404F