Ammonia Fitting of Multiple Velocity Components in High-Mass Star-Forming Regions

We perform a multiple velocity component analysis of ammonia (NH$_3$) gas from KEYSTONE, a Green Bank Telescope survey covering 11 giant molecular clouds (GMCs) at distances from 0.7 to 2.7 kpc. We extend existing codes to enable simultaneous fitting of up to three velocity components in NH$_3$ (1,1) with radiative transfer. Using our multiple component fitting technique, we produce the best maps of the centroid velocity and velocity dispersion in these clouds to date. Over the entire survey, multiple velocity components were seen in 13% of pixels where we detect and fit NH$_3$ emission, primarily in clusters at the heart of the GMCs. In these multiple component pixels, the median measured NH$_3$ linewidth decreased by a factor of 1.4 compared to equivalent single-component measurements, but there are also significant cloud-to-cloud variations. Regions with multiple velocity components tend to be found in the densest zones of the GMCs and at the sites of high-mass star formation, indicative of multiple filaments, cores, or complex velocities associated with the formation of massive stars. Disentangling these velocity features will allow future quantitative analysis of coherent motions, such as infall and outflow, in these complex environments. The multi-component data products are available on the CADC.