Tracing Magnetic Field Morphology Using the Velocity Gradient Technique in the Presence of CO Self-absorption

Hsieh, Cheng-Han; Hu, Yue; Lai, Shih-Ping; Yuen, Ka Ho; Liu, Sheng-Yuan; Hsieh, I-Ta; Ho, K.L.; Lazarían, A.

doi:10.3847/1538-4357/ab0376

Cited by 30 publications

(22 citation statements)

References 50 publications

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“…While we only have two gas tracers, the available high S/N Planck data in the region allows us to draw a global picture of the interplay between the molecular cloud and the magnetic field. Hsieh et al (2019) showed that the VGs could safely be applied to both optically thin and optically thick gas tracers to infer the magnetic field morphology. In the northern part, the IGs and VGs derived from 12 CO and 13 CO data (Fig.…”

Section: Toward a Cloud Tomographymentioning

confidence: 99%

Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

Alina

Montillaud

et al. 2022

A&A

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Context. The role of large-scale magnetic fields in the evolution of star-forming regions remains elusive. Its investigation requires the observational characterization of well-constrained molecular clouds. The Monoceros OB 1 molecular cloud is a large complex containing several structures that have been shown to be engaged in an active interaction and to have a rich star formation history. However, the magnetic fields in this region have only been studied on small scales. Aims. We study the large-scale magnetic field structure and its interplay with the gas dynamics in the Monoceros OB 1 east molecular cloud. Methods. We combined observations of dust polarized emission from the Planck telescope and CO molecular line emission observations from the Taeduk Radio Astronomy Observatory 14-metre telescope. We calculated the strength of the plane-of-sky magnetic field using a modified Chandrasekhar-Fermi method and estimated the mass-over-flux ratios in different regions of the cloud. We used the comparison of the velocity and intensity gradients of the molecular line observations with the polarimetric observations to trace dynamically active regions. Results. The molecular complex shows an ordered large-scale plane-of-sky magnetic field structure. In the northern part, it is mostly orientated along the filamentary structures, while the southern part shows at least two regions with distinct magnetic field orientations. Our analysis reveals a shock region in the northern part right between two filamentary clouds that, in previous studies, were suggested to be involved in a collision. The magnetic properties of the north-main and north-eastern filaments suggest that these filaments once formed a single one, and that the magnetic field evolved together with the material and did not undergo major changes during the evolution of the cloud. In the southern part, we find that either the magnetic field guides the accretion of interstellar matter towards the cloud or it is dragged by the matter falling towards the main cloud. Conclusions. The large-scale magnetic field in the Monoceros OB 1 east molecular cloud is tightly connected to the global structure of the complex. In the northern part, it seems to serve a dynamically important role by possibly providing support against gravity in the direction perpendicular to the field and to the filament. In the southern part, it is probably the most influential factor governing the morphological structure by guiding possible gas inflow. A study of the whole Monoceros OB 1 molecular complex at large scales is necessary to form a global picture of the formation and evolution of the Monoceros OB 1 east cloud and the role of the magnetic field in this process.

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Section: Toward a Cloud Tomographymentioning

confidence: 99%

Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

Alina

Montillaud

et al. 2022

A&A

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“…8, we provide a brief description of the gradient dispersion and how this can be used for deriving M A . We use three super-sonic MHD simulations with different M A and apply radiative transfer code SPRAX 30 to them (see Lazarian et al (2018) 31 for details about the numerical cubes). The Supplementary Fig.…”

Section: /14mentioning

confidence: 99%

“…The VGT has been numerically tested for a wide range of column densities from diffuse transparent gas 19,28,29 to molecular self-absorbing dense gas 30 . It was shown to be able to provide both the orientations of the magnetic field as well as a measure of media magnetization 31,32 .…”

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Magnetic field morphology in interstellar clouds with the velocity gradient technique

Hu¹,

Yuen²,

Lazarian³

et al. 2019

Nat Astron

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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 field, measuring the magnetization of interstellar media and estimating the fraction of gravitational collapsing gas in molecular clouds using spectral line observations. In this paper, 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 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 means of 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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“…4, v 0 is the velocity corresponding to the peak position in PPV's velocity profile. The validity of these two methods have been test in both numerical simulations (Hsieh et al 2019;Lazarian & Yuen 2018a) and observational data (Hu et al 2019b,a).…”

Section: Probability Density Functionmentioning

confidence: 99%

“…The ability of VGT to trace magnetic fields in turbulent media has been tested in numerical simulations (Hsieh et al 2019;Hu et al 2018;Yuen & Lazarian 2017b) and by comparing with observational polarization maps (Hu et al 2019a,b;González-Casanova & Lazarian 2019;Hu et al 2020a). These studies also reveal that a new effect takes place in the presence of self-gravity.…”

Section: Introductionmentioning

confidence: 99%

Velocity Gradient in the Presence of Self-Gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage

Hu,

Lazarian,

Yuen

2020

Preprint

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Understanding how star formation is regulated requires studying the energy balance between turbulence, magnetic fields, feedback, and gravity within molecular clouds. However, identifying the transition region where the gravity takes over and collapse occurs remains elusive. Recent studies of the Velocity Gradient Technique (VGT), which is an advanced tool for magnetic field studies, reveal that the velocity gradient changes its direction by 90 • with respect to the magnetic field in the regions of gravitational collapse. In this study, we confirm that the self-gravity induces the change of orientation and high gradient amplitude for both the velocity gradient and intensity gradient. We explore two ways of identifying self-gravitating regions through the doublepeak feature in the histogram of gradients' orientation and the curvature of gradients. We show that velocity gradients' morphology and amplitude can be synthetically used to trace the convergent inflows. By comparing with the column density Probability Density Functions method, we show that VGT is a powerful new tool for studying the gas dynamics and tracing magnetic field in star-forming regions. By analogy with VGT, we extend the Intensity Gradient Technique (IGT) to locate the gravitational collapsing region and shock. We show that the synergy of VGT and IGT can determine the collapsing stages in a star-forming region. We conclude that star formation can happen very successfully in strongly magnetized and fully ionized media.

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Tracing Magnetic Field Morphology Using the Velocity Gradient Technique in the Presence of CO Self-absorption

Cited by 30 publications

References 50 publications

Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

Large-scale magnetic field in the Monoceros OB 1 east molecular cloud

Magnetic field morphology in interstellar clouds with the velocity gradient technique

Velocity Gradient in the Presence of Self-Gravity: Identifying Gravity-induced Inflow and Determining Collapsing Stage

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