Science with an ngVLA: Star-forming Filaments and Cores on a Galactic
  Scale
  Continuum observations of molecular clouds have revealed a surprising amount
of substructure in the form of filaments of a few pc length and cores of ~0.1
pc diameter. Understanding the evolution of these substructures towards star
formation requires the kinematic and dynamical insights provided uniquely by
sensitive line observations at high angular and spectral resolution. In this
short paper, we describe how an ngVLA can probe effectively the dynamics of
filaments and cores in nearby star-forming molecular clouds using the NH3
rotation-inversion transitions at 24 GHz. Such emission has been proven to
trace well the high column density environments of star-forming cores and
filaments but higher-resolution observations are needed to reveal important
details of how dense gas is flowing within and onto these substructures. In
particular, we describe how 150 x 18-m antennas with a maximum baseline of 1 km
can be used to map sensitively NH3 emission across high column density
locations in clouds in roughly an order of magnitude less time than with the
current Jansky VLA.
