Measuring magnetic fields in the interstellar medium and obtaining their distribution along line-of-sight (LOS) is very challenging with the traditional techniques. The Velocity Gradient Technique (VGT), which utilizes anisotropy of magnetohydrodynamic turbulence, provides an attractive solution. Targeting the central molecular zone (CMZ), we test this approach by applying the VGT to $\rm ^{12}CO$ and $\rm ^{13}CO$ (J = 1–0) data cubes. We first used the scousepy algorithm to decompose the CO line emissions into separate velocity components, and then we constructed pseudo-Stokes parameters via the VGT to map the plane-of-the-sky magnetic fields in three-dimension. We present the decomposed magnetic field maps and investigate their significance. While the LOS integrated magnetic field orientation is shown to be consistent with the polarized dust emission from the Planck survey at 353 GHz, individual velocity components may exhibit different magnetic fields. We present a scheme of magnetic field configuration in the CMZ based on the decomposed magnetic fields. In particular, we observe a nearly vertical magnetic field orientation in the dense clump near the Sgr B2 and a change in the outflow regions around the Sgr A*. Two high-velocity structures associated with an expanding ring in the CMZ show distinct swirling magnetic field structures. These results demonstrate the potential power of the VGT to decompose velocity or density-dependent magnetic structures.
Interaction of three-dimensional magnetic fields, turbulence, and self-gravity in the molecular cloud is crucial in understanding star formation but has not been addressed so far. In this work, we target the low-mass star-forming region L1688 and use the spectral emissions of 12CO, 13CO, C18O, and H i, as well as polarized dust emissions. To obtain the 3D direction of the magnetic field, we employ the novel polarization fraction analysis. In combining with the plane-of-the-sky (POS) magnetic field strength derived from the Davis–Chandrasekhar–Fermi (DCF) method and the new differential measure analysis (DMA) technique, we present the first measurement of L1688’s three-dimensional magnetic field, including its orientation and strength. We find that L1688’s magnetic field has two statistically different inclination angles. The low-intensity tail has an inclination angle ≈55° on average, while that of the central dense clump is ≈30°. We find the global mean value of total magnetic field strength is Btot ≈ $135 \,\mathrm{\mu }{\rm G}$ from DCF and Btot ≈ $75 \,\mathrm{\mu }{\rm G}$ from DMA. We use the velocity gradient technique (VGT) to separate the magnetic fields’ POS orientation associated with L1688 and its foreground/background. The magnetic fields’ orientations are statistically coherent. The probability density function of H2 column density and VGT reveal that L1688 is potentially undergoing gravitational contraction at large scale ≈1.0 pc and gravitational collapse at small scale ≈0.2 pc. The gravitational contraction mainly along the magnetic field resulting in an approximate power-law relation $B_{\rm tot}\propto n_{\rm H}^{1/2}$ when volume density nH is less than approximately 6.0 × 103 cm−3.
more » « less- NSF-PAR ID:
- 10435606
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 524
- Issue:
- 3
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- p. 4431-4446
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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