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arXiv 1901.06196astro-ph.GA
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用PILOT测量中心分子区磁场的几何形状

The geometry of the magnetic field in the Central Molecular Zone measured by PILOT

A. Mangilli, J. Aumont, J. -Ph. Bernard, A. Buzzelli, G. de Gasperis, J. B. Durrive, K. Ferrière, G. Foënard, A. Hughes, A. Lacourt, R. Misawa, L. Montier, B. M… 展开作者

A. Mangilli, J. Aumont, J. -Ph. Bernard, A. Buzzelli, G. de Gasperis, J. B. Durrive, K. Ferrière, G. Foënard, A. Hughes, A. Lacourt, R. Misawa, L. Montier, B. Mot, I. Ristorcelli, H. Roussel, P. Ade, D. Alina, P. de Bernardis, E. de Gouveia Dal Pino, J. P. Dubois, C. Engel, P. Hargrave, R. Laureijs, Y. Longval, B. Maffei, A. M. Magalhães, C. Marty, S. Masi, J. Montel, F. Pajot, L. Rodriguez, M. Salatino, M. Saccoccio, S. Stever, J. Tauber, C. Tibbs, C. Tucker

摘要:

我们提出了第一个远红外(FIR)尘埃发射偏振图,涵盖了整个银河系的中央分子区(CMZ)。这些数据是用PILOT球载实验获得的,覆盖了银河系中心区域$-2\,^\circ<l<2\,^\circ$、$-4\,^\circ<b<3\,^\circ$,波长为240 $μ$ m,角分辨率为$2.2\,'$。从我们测量的尘埃极化角,我们推断出一个磁场方向投射到天空的平面上,是显着有序的CMZ的整个范围内,与一个平均倾斜角$\simeq 22\,^\circ$顺时针相对于银河系平面。我们的研究结果证实了以前的说法,跟踪尘埃偏振发射的字段是定向的GHz的无线电同步辐射跟踪在银河系中心区域的字段几乎正交。观察到的场结构与353 GHz和217 GHz的最新普朗克极化数据在全球范围内兼容。在我们的数据中扣除扩展发射后,我们得到的平均场取向与JCMT在20 km/s和50 km/s分子云中以较高角分辨率测量的平均场取向有很好的一致性。我们没有发现任何证据表明,磁场方向是有关的100 pc的扭曲环结构内的CMZ。我们建议,在银河系中心区域的低极化分数和高度有序的投影场的方向可以调和,如果字段是强的,与3D几何形状,这是主要面向$\simeq 15\,^\circ$相对于视线朝向银河系中心。假设磁压力和冲压压力之间的均分,我们得到的磁场强度估计高达几个mG的几个CMZ分子云。

英文摘要:

We present the first far infrared (FIR) dust emission polarization map covering the full extent Milky Way's Central molecular zone (CMZ). The data, obtained with the PILOT balloon-borne experiment, covers the Galactic Center region $-2\,^\circ<l<2\,^\circ$, $-4\,^\circ<b<3\,^\circ$ at a wavelength of 240 $μ$m and an angular resolution $2.2\,'$. From our measured dust polarization angles, we infer a magnetic field orientation projected onto the plane of the sky that is remarkably ordered over the full extent of the CMZ, with an average tilt angle of $\simeq 22\,^\circ$ clockwise with respect to the Galactic plane. Our results confirm previous claims that the field traced by dust polarized emission is oriented nearly orthogonal to the field traced by GHz radio synchrotron emission in the Galactic Center region. The observed field structure is globally compatible with the latest Planck polarization data at 353 GHz and 217 GHz. Upon subtraction of the extended emission in our data, the mean field orientation that we obtain shows good agreement with the mean field orientation measured at higher angular resolution by the JCMT within the 20 km/s and 50 km/s molecular clouds. We find no evidence that the magnetic field orientation is related to the 100 pc twisted ring structure within the CMZ. We propose that the low polarization fraction in the Galactic Center region and the highly ordered projected field orientation can be reconciled if the field is strong, with a 3D geometry that is is mostly oriented $\simeq 15\,^\circ$ with respect to the line-of-sight towards the Galactic center. Assuming equipartition between the magnetic pressure and ram pressure, we obtain magnetic field strengths estimates as high as a few mG for several CMZ molecular clouds.

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