Levine E S, Blitz Leo, Heiles Carl
Astronomy Department, University of California, 601 Campbell Hall, Berkeley, CA 94720, USA.
Science. 2006 Jun 23;312(5781):1773-7. doi: 10.1126/science.1128455. Epub 2006 Jun 1.
We produce a detailed map of the perturbed surface density of neutral hydrogen in the outer Milky Way disk, demonstrating that the Galaxy is a non-axisymmetric multiarmed spiral. Spiral structure in the southern half of the Galaxy can be traced out to at least 25 kiloparsecs, implying a minimum radius for the gas disk. Overdensities in the surface density are coincident with regions of reduced gas thickness. The ratio of the surface density to the local median surface density is relatively constant along an arm. Logarithmic spirals can be fit to the arms with pitch angles of 20 degrees to 25 degrees .
我们绘制了一幅银河系外盘中性氢扰动面密度的详细地图，表明银河系是一个非轴对称的多旋臂螺旋星系。银河系南半部分的螺旋结构至少可以追溯到25千秒差距，这意味着气体盘的最小半径。面密度的过密区域与气体厚度减小的区域重合。沿着一条旋臂，面密度与局部中值面密度的比值相对恒定。对数螺旋线可以拟合到 pitch 角为20度到25度的旋臂上。 （注：原文中“pitch angles”可能是“螺距角”，这里直接保留英文未翻译，因为不确定具体准确的中文术语）
