我們展示了在BISTRO調查計畫中，利用裝設在JCMT望遠鏡上的SCUBA2相機與POL-2偏振儀對銀河系中心所作的450微米與850微米偏振觀測。這些數據提供我們在20公里每秒分子雲(20 km s−1 cloud)、50公里每秒分子雲( km s−1 cloud)與人馬座A*附近高解析度的照片(450微米觀測的解析度約為0.39秒差距，而850微米觀測的解析度約為0.59秒差距)。投影在天球平面上的磁場方向大致對應塵埃分布的結構，並且磁場方位角擾動的標準差約為7度。我們利用多重高斯曲線擬合區分出外圍物質結構與嵌入在內部的核心。根據450微米與850微米觀測數據推測出的整體磁場強度，最常見的數值約為200微高斯，並且在20公里每秒分子雲與50公里每秒分子雲的區域，我們發現外部磁場強度約為內部磁場強度的1.5倍。通過質量與磁通量的比率，在接近20公里每秒分子雲與50公里每秒分子雲的環境，將以重力作為主導，使得物質向內塌縮；反之，在其餘區域則以磁場作為主導，並且抵抗向內塌縮的趨勢。除了重力以外，藉由等離子體環境參數Beta值，顯示磁能密度遠高於熱能密度；再者，藉由阿爾文馬赫數能得知，湍流造成的影響也比磁場來的小。因此我們認為磁場在抑制銀河系中心恆星形成過程中扮演至關重要的角色。此外，藉由偏極化程度與輻射強度的冪次指數，不論在450微米或者850微米的數據都約為-0.4，表明在此區域中，塵埃顆粒的旋轉很好地與磁場對齊。

We present the 450um and 850um polarietric observations toward the galactic center, which are parts of the James Clerk Maxwell Telescope (JCMT) B-Fields In Star-Forming Region Observations (BISTRO) Survey using POL-2 polarimeter on Sub-millimetre Common-User Bolometer Array 2 (SCUBA-2) camera. These measurements provide us the high spatial resolution (∼0.39 pc at 450 µm and ∼0.59 pc at 850 µm) to probe the magnetic field in the vicinity of 20 km s−1 cloud, 50 km s−1 cloud and SgrA*. The inferred magnetic field orientation on plane-of sky is organized following the extension of dust structure, and the overall angle dispersion is ∼7 ◦ at both wavelengths. We utilize the multiple Gaussian fitting to separate the gas structures into the ambient material and the embedded cores, and estimate the plane-of-sky magnetic field strengths using the Davis-Chandrasekhar Fermi method. The most common magnetic field strength is ∼200µG for both 450 µm and 850 µm. Within the regions of 20 km s−1 cloud and 50 km s−1 cloud, the outer magnetic field strengths are roughly 1.5 times stronger than the inner magnetic field strengths. Based on mass-to-flux ratio, the environments closed to 20 km s−1 cloud and 50 km s−1 cloud are dominated by the gravity, while in the remaining area, the magnetic field is dominant. Apart from the gravity, the magnetic energy density is much stronger than the thermal energy density because of plasma beta β ≪ 1, and also more influential than turbulence with the Alfv´en Mach Number MA < 1. Therefore, we suggest the magnetic field plays the crucial role to suppress the star formation around the galactic center. Additionally, we find the polarization fraction is proportional to the intensity with power law index of −0.395 and −0.354 at 450 µm and 850 µm in high S/N limit, indicating the dust grains are well aligned with the magnetic fields.

Contents
Abstract (Chinese) I
Abstract II
Contents III
List of Figures V
List of Tables X
1 Introduction 1
1.1 Magnetic field and star formation . . . . . . . . . . . . . . . . . . . 1
1.2 Central-Molecular-Zone (CMZ) . . . . . . . . . . . . . . . . . . . . 1
1.3 Davis-Chandrasekhar-Fermi method . . . . . . . . . . . . . . . . . . 2
1.4 Grain alignment theory . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Observations 5
2.1 BISTRO Polarimetric Continuum data . . . . . . . . . . . . . . . . 5
2.2 CHIMPS 13CO J = 3 → 2 Emission . . . . . . . . . . . . . . . . . . 7
2.3 Herschel Hi-GAL data . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Results and Analysis 11
3.1 Magnetic Field Morphology . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Magnetic Field Strength . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2.1 Angular Dispersion around galactic center . . . . . . . . . . 16
3.2.2 Velocity Dispersion . . . . . . . . . . . . . . . . . . . . . . . 21
3.2.3 Volume Density . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.4 Magnetic Field strength . . . . . . . . . . . . . . . . . . . . 36
3.3 Dust Grain Alignment . . . . . . . . . . . . . . . . . . . . . . . . . 41
4 Discussion 44
4.1 Magnetic field vs. Gravity . . . . . . . . . . . . . . . . . . . . . . . 44
4.2 Magnetic field vs. Thermal energy . . . . . . . . . . . . . . . . . . . 47
4.3 Magnetic field vs. Turbulence . . . . . . . . . . . . . . . . . . . . . 47
5 Conclusion 51
Bibliography 53

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