The alignment of molecular cloud magnetic fields with the spiral arms in M33

摘要

The formation of molecular clouds, which serve as stellar nurseries in galaxies, is poorly understood. A class of cloud formation models suggests that a large-scale galactic magnetic field is irrelevant at the scale of individual clouds, because the turbulence and rotation of a cloud may randomize the orientation of its magnetic field1'2. Alternatively, galactic fields could be strong enough to impose their direction upon individual clouds3'4, thereby regulating cloud accumulation and fragmentation5, and affecting the rate and efficiency of star formation6. Our location in the disk of the Galaxy makes an assessment of the situation difficult. Here we report observations of the magnetic field orientation of six giant molecular cloud complexes in the nearby, almost face-on, galaxy M33. The fields are aligned with the spiral arms, suggesting that the large-scale field in M33 anchors the clouds.%人们提出了很多机制来解释星系恒星形成,该rn过程被认为主要发生在富含尘埃和气体的星际rn分子云中.一些"云形成模型"认为,是否存rn在一个大型星系磁场在各个星际分子云的尺度rn上来说无关紧要,而另一些模型则认为,星系rn磁场强到足以将其方向施加到各个星际分子云rn上.利用安装在莫纳克亚山上的"亚毫米阵rn列"望远镜,Hua-bai Li和Thomas Henning对rn来自"三角座"中的M33星系的磁场进行了观rn测.这个星座是离我们最近的、面朝我们的星rn座,有显著的光螺旋臂.他们发现了六个巨大rn的分子云团,这几个云团全都与那些螺旋臂的rn方向一致,说明M33中的大型磁场固定了这些rn云的方向.