Mapping Magnetic Field Structure in Star-forming Regions

賴詩萍

Oct 4, 2006, NTHU Phys Colloquium

康德 - 拉普拉斯 星雲假說

康德 (1755 年 ) - 原始星雲是由大小不等的固體微粒組成的 “﹐ 天體在吸引最強的地方開始形成”﹐萬有引力使得微粒相互接近。

拉普拉斯 (1796 年 ) - 形成太陽系的雲是一團巨大的﹑灼熱的﹑轉動著的氣體﹐大致呈球狀。由於冷卻﹐星雲逐漸收縮 , 星雲的中心部分凝聚成太陽 。

Star formation standard model

Shu et al. 1987

Shu et al. (1987)

Star formation standard model

P. Andre

Starless Cores – Barnard 68

Simplest Star Formation TheorySimplest Star Formation Theory

Thermal pressure supportThermal pressure support - Jeans Mass (1928)

GravitationThermal Pressure

Why B is important in star formation?

Regulating star formation efficiency Observed star formation efficiency is low

Theoritical 200 M/year >> Observed 3 M/year B provides support in

Static fields MHD waves (turbulence)

Facilitating gravitational collapse Angular momentum problem – magnetic braking Magnetic flux problem - ambipolar diffusion

Magnetic support theoriesMagnetic support theories

MHD simulationsMHD simulations (Ostriker, Gammie, & Stone 1999)

Morphology EvolutionMorphology Evolution

2

2

A

s

V

c large -> random

morphology

How to measure B?How to measure B?

Zeeman Effect – Too Difficult!!Polarization of Dust Emission: PBp

Polarized Molecular Line Emission (the Goldreich-Kylafis Effect): PBp or PBp

BV

Polarization Observations with Polarization Observations with Berkeley-Illinois-Maryland Array Berkeley-Illinois-Maryland Array

(BIMA)(BIMA)

Dust Polarization observations with BIMA

Magnetic Field MorphologyMagnetic Field Morphology – W51 e1/e2JCMT JCMT 14” at 850 14” at 850 mm BIMA BIMA 2” at 1.3 mm 2” at 1.3 mm

Lai et al. (2001)Chrysostomou et al. (2002)

NGC 2024NGC 2024

Matthews et al. (2002)

JCMT JCMT 14” at 850 14” at 850 mm BIMA BIMA 2” at 1.3 mm 2” at 1.3 mm

Lai et al. (2002)

DR21(OH) – JCMT vs. BIMA

(B map)

Lai et al. (2003)

NGC1333 IRAS4A

NGC1333 IRAS4A

Twisted hour-Twisted hour-glass glass geometrygeometry

NGC1333 IRAS4A

BIMA BIMA 2” at 1.3 mm 2” at 1.3 mm SMA SMA 1” at 850 1” at 850 mm

Lai (2002) Girart, Rao, Marrone (2006)

Physical quantitiesPhysical quantities

Dispersion of Polarization Angle (Dispersion of Polarization Angle ())1. Field Strengths (the Chandrasekhar-Fermi Method)

2. Mass-to-magnetic-flux Ratios

3. Turbulent-to-magnetic-energy Ratios

Dispersion of Polarization Angle (Dispersion of Polarization Angle ())

⇒ Field Strengths in the plane of sky

• Uniform fields perturbed by MHD turbulence -

• Incompressible fluid - invariant

• Small perturbation -

• Isotropic turbulence -

Chandrasekhar-Fermi MethodChandrasekhar-Fermi Method

B

B

4

B

losp

Ostriker, Stone, & Gammie 2001

Results Bp ~ 0.8 – 3.5 mG

M/ΦΦB,p ~ 0.1 – 4.9 critical mass-to-flux ratio

turb ~ 0.03 – 0.4

⇒ BBpp, M/, M/ΦΦB,pB,p, , turbturb

Future Work – More observations!!Future Work – More observations!!

Current/Future instrumentsCurrent/Future instrumentsSMA (the only working interferometer for now)CARMA = BIMA + OVRO (?)ALMA!! (wait at least 7 years)

3D Magnetic Field Structure3D Magnetic Field StructureZeeman measurements

High density (106 cm-3) - CNYoung Cores – CCS

Line polarization

ALMA in 7 years

廣告時間

“Star and Planet formation” Journal Club時間 : 隔週週二中午 12:10-1:00 pm地點 : 502A目的

輪流報告最新的研究結果培養學生對這個研究主題的興趣

參與老師 : 江瑛貴 , 陳惠茹 , 呂聖元 , 賴詩萍