SOF09231

Testing a new method for identifying regions of gravitational collapse within a magnetized molecular cloud using HAWC+ and GBT/ARGUS

Abstract

Understanding how star formation is regulated requires studying the energy balance between turbulence,
magnetic fields, feedback and gravity within molecular clouds. Here we propose to use HAWC+ to test a
promising new method for both (a) identifying regions within clouds that are gravitationally collapsing, and (b)
characterizing the relative importance of magnetic fields, turbulence and self-gravity within clouds. This
method is based on predictions from the Velocity Gradient Technique (VGT), that in collapsing regions of
molecular clouds the spatial velocity gradients will rotate by 90deg to align parallel to the magnetic field. Such
rotations mark the transition from a magnetic field and turbulence dominated regime at low densities, to higher
density regions that are collapsing under gravity. VGT rotations towards high density clumps have been
observed in simulations and in low resolution (10' FWHM) comparisons between Planck inferred magnetic field
maps and velocity gradients derived from molecular line observations. However Planck cannot resolve
magnetic fields within dense gas clumps and filaments. Here we propose to make high resolution (19'' FWHM)
HAWC+ Band E polarization observations of the nearby dense clump L1551 that shows a change in velocity
gradient orientation with respect to the magnetic field at Planck resolution. We also request GBT/ARGUS
spectral line observations of HCN and HCO+ to make VGT maps at the same resolution as our HAWC+ data.
With these data we will (1) determine whether the rotations of velocity gradients to align parallel with the
magnetic field predicted by the VGT method do exist, (2) use the VGT to identify the boundary of the self-
gravitating region within L1551, and (3) determine the transition density, which will allow us to estimate the
magnetic field strength of L1551. Validation of this VGT technique with HAWC+ observations would provide
a powerful new tool for studying gas dynamics in star formation.

Investigators

Name	Institution
Yue Hu	Wisconsin at Madison, University of
Laura Fissel	Northwestern University; Queen's University
Alexander Lazarian *	Wisconsin at Madison, University of

* indicates the PI