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Magnetic field morphology in interstellar clouds with the velocity gradient technique


Magnetic fields, while ubiquitous in many astrophysical environments, are challenging to measure observationally. Based on the properties of anisotropy of eddies in magnetized turbulence, the velocity gradient technique is a method synergistic to dust polarimetry that is capable of tracing plane-of-the-sky magnetic fields, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. Here, we apply this technique to five low-mass star-forming molecular clouds in the Gould Belt and compare the results to the magnetic field orientation obtained from polarized dust emission. We find that the estimates of magnetic field orientations and magnetization for both methods are statistically similar. We estimate the fraction of collapsing gas in the selected clouds. By using the velocity gradient technique, we also present the plane-of-the-sky magnetic field orientation and magnetization of the Smith Cloud, for which dust polarimetry data are unavailable.

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Fig. 1: The magnetic field morphology of Taurus obtained with the VGT using 13CO and the Planck polarimetry.
Fig. 2: The magnetic field morphology of molecular clouds L 1551, Perseus A, NGC 1333 and Serpens obtained with the VGT using 13CO and Planck polarimetry.
Fig. 3: The magnetic field morphology and magnetization of the Smith Cloud superimposed on a map of its total H i intensity.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author and other co-authors upon reasonable request.

Code availability

The code for the VGT algorithm is available at


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A.L. acknowledges the support of National Science Foundation (NSF) grants AST 1715754 and 1816234, and NASA grant NNX14AJ53G. The research of P.F.G. was carried out at the Jet Propulsion Laboratory, which is operated for NASA by the California Institute of Technology. We acknowledge M. Heyer for a number of valuable suggestions in improving our paper. We acknowledge the COordinated Molecular Probe Line Extinction Thermal Emission Survey of Star Forming Regions (COMPLETE) for providing a range of data for the Perseus region and the Arizona Radio Observatory for providing the data of the Serpens region and NGC 1333. The Green Bank Observatory is a facility of the NSF operated under a cooperative agreement by Associated Universities, Inc. This work is based on observations obtained with Planck (, an ESA science mission with instruments and contributions directly funded by the ESA Member States, NASA and Canada.

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Authors and Affiliations



All authors discussed the results, commented on the manuscript and contributed to the writing of the manuscript. Y.H., K.H.Y. and A.L. conceived the project, Y.H., K.H.Y. and K.W.H. performed calculations, while Y.H., K.H.Y., V.L. and A.L. analysed the results and wrote the original manuscript. R.A.B. provided suggestions on how the VGT technique might be applied to the Smith Cloud. The data on the Taurus cloud were provided by P.F.G. and data on the Smith Cloud were provided by A.S.H. and F.J.L.

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Correspondence to Yue Hu.

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Journal peer review information: Nature Astronomy thanks Andrea Bracco, Kate Pattle and Thomas H. Troland for their contribution to the peer review of this work.

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Supplementary Figures 1–5, Supplementary Table 1 and Supplementary References 1–18.

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Hu, Y., Yuen, K.H., Lazarian, V. et al. Magnetic field morphology in interstellar clouds with the velocity gradient technique. Nat Astron 3, 776–782 (2019).

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