Surveying Magnetic Field with Velocity Gradient Technique in - - PowerPoint PPT Presentation

Surveying Magnetic Field with Velocity Gradient Technique in Molecular Clouds

Speaker：Yue Hu Date：2/11/2018

CONTENT

• 1. Introduction
• 2. Morphology of Magnetic Field
• 3. Magnetization Level
• 4. Prediction for Smith Cloud

Magnetic Field Turbulence Gravity

• 1. Introduction

The dynamics of the ISM

Emag Etur Egrav

≈

>>

The role of the magnetic field in ISM

• 1. Introduction

Galaxy Molecular Cloud Dense Cores Protostar Galaxies ~100,000 light years Molecular Clouds ~100 light years Dense Cores ~ light years Protostar ~ light hours

The magnetic field regulates the formation and evolution of both large and small scale structures

Dust Polarization

Available in dusty ISM

Synchrotron Emission Zeeman Splitting Faraday Rotation

• 1. Introduction

The approach to study the magnetic field

Planck collaboration (2014) Planck collaboration (2015) Oppermann et al. (2012) Crutcher et al. (2010) 

B

Orientation of Available in CR-filled ISM Orientation and Strength of



B

Available in neutral region Strength and sign of

//

B

Available in ionized region Strength and sign of

//

B

Instrument complexity Planck Billion dollars cost ALMA

• 1. Introduction

Limitation of polarization

Insufficient polarization percentage

Credits: Brandon Hensley

• 1. Introduction

The Velocity Gradients Technique

B-field Turbulent eddies Gradient Gradient Gradients Smaller scale = more anisotropic mean B - field direction

• K. H. Yuen and A.
• Lazarian. ApJ,

837:24, 2017.

• 2. Tracing The Morphology of the Magnetic Field

Observational Data on Molecular Clouds

Perseus (13CO) FCRAO telescope NGC 1333 (13CO) Heinrich Hertz Submillimeter telescope Taurus (13CO) Quabbin millimeter wave telescope Serpens (13CO) Heinrich Hertz Submillimeter telescope L 1551 (13CO) Nobeyama Radio Observatory 45m telescope Smith Cloud Green Bank telescope (H I data)

Agreement with Planck Polarization (353GHz)

Taurus 13CO

Velocity Gradients Technique

Taurus Planck

Planck Dust Polarization

• 2. Tracing The Morphology of the Magnetic Field

Agreement with Planck Polarization (353GHz)

Serpens

) 2 1 cos ( 2

2

     AM

θ is the relative angle between gradients and Planck polarization

Cloud Region Emission Line AM Taurus

13CO: J=1-0

0.75 Perseus A

13CO: J=1-0

0.70 Serpens

13CO: J=1-0

0.78 NGC 1333

13CO: J=2-1

0.77 L 1551

13CO: J=2-1

0.82

• 2. Tracing The Morphology of the Magnetic Field

AM=1 AM = -1

perpendicular parallel

L 1551 NGC 1333

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Prediction for Smith Cloud

Smith Cloud

Saxton/Lockman/NRAO/AUI/NSF/Mellinger

Smith Cloud: a high-velocity diffuse H I cloud, with no detected dust, the morphology of the magnetic field cannot be investigated using dust polarimetry.

• 2. Tracing The Morphology of the Magnetic Field

Low MA Angle Bins Angle Bins

• 3. Magnetization Level

Correlation between VGs and MA High MA

Strong B-field Weak B-field

less dispersed More dispersed

Orientation of VGs Orientation of VGs

power law

               

2 2

sin cos 1 , 09 . ) 1 ( 06 . 1 , 09 . ) 1 ( 14 . R M R M M R M

A A A A

Lazarian et al 2018

• 3. Magnetization Level

25° 27° 29°

Dec.

23°

5 10 15 20 25

Magnetization (MA-1)

1.25 0.50 1.00 0.75

Taurus

13CO J = 1-0

AM=0.75

TA*[K km/s]

Quabbin millimeter-wave telescope

Magnetization Distribution

• 1. Direction: gradients
• 2. Color: magnetization
• 3. Angle Δθ : uncertainty

bowtie mark

Agreement with Planck Polarization (353GHz)

Serpens NGC 1333 L 1551

Cloud MA (Pol) MA (VGT) Taurus 1.11 1.18 Perseus A 1.20 1.14 Serpens 0.76 0.89 NGC 1333 0.95 0.83 L 1551 0.67 0.79

• 3. Magnetization Level

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• 4. Prediction of Smith Cloud

Smith Cloud

Saxton/Lockman/NRAO/AUI/NSF/Mellinger

Smith Cloud: a high-velocity diffuse H I cloud, with no detected dust, the morphology of the magnetic field cannot be investigated using dust polarimetry.

B// ≥ 3μG, consistent with the estimate of Hill et al (2013)

Prediction for Smith Cloud

Thank you!