圆规星系中的大尺度原子分子气体
The Large-Scale Atomic and Molecular Gas in the Circinus Galaxy
摘要：
我们利用ATCA和SEST对圆规星系附近的大尺度原子和分子气体进行了成像。圆规座的HI镶嵌图显示了单点图像中显示的位置角和倾角的扭曲，这两者似乎都超出了先前成像的内部30 kpc。分子气体已在两个CO跃迁中进行了映射，其中我们推导出总分子气体质量为~ 2 e9 Mo。在3 kpc的半径内，即CO被清楚地检测到的地方，分子分数随着接近核而从~0.7急剧攀升到1。我们的HI镶嵌图给出了~ 6 e9 Mo的原子气体质量，这是完全映射的单碟值的70%。因此，总的中性气体质量与动力质量的比率为3%，与圆规座的SAS 3分类一致。先前发现的高（分子）气体质量分数，只发生在接近中心~0.5 kpc的地方，在这个区域内外都下降到< 10%，减轻了先前关于将银河系转换率应用于圆规座的有效性的担忧。由HI和CO所描绘的旋转曲线在约1 kpc处呈现出陡峭的倾斜，这是原子/分子环的边缘，在那里发生了星暴。我们发现原子和分子气体跟踪不同的运动学特征，并认为，最快的部分sub-kpc环绝大多数分子气体。超过内部kpc，速度攀升，在>10 kpc时进入固体旋转。大部分的星光都是从这个半径范围内发出的，而且如此多的动力学质量（它仍然在攀升到我们数据的极限（>50 kpc）），必须归因于暗物质晕。
英文摘要：
We have used the ATCA and the SEST to map the large-scale atomic and molecular gas in the nearby Circinus galaxy. The HI mosaic of Circinus exhibits the warps in position angle and inclination revealed in the single-pointing image, both of which appear to settle beyond the inner 30 kpc which was previously imaged. The molecular gas has been mapped in both the CO transitions, where we derive a total molecular gas mass of ~2e9 Mo. Within a radius of 3 kpc, i.e. where CO was clearly detected, the molecular fraction climbs steeply from ~0.7 to unity with proximity to the nucleus. Our HI mosaic gives an atomic gas mass of ~6e9 Mo which is 70% of the fully mapped single dish value. The total neutral gas mass to dynamical mass ratio is therefore 3%, consistent with the SAS3 classification of Circinus. The high (molecular) gas mass fraction found previously, only occurs close to the central ~0.5 kpc and falls to < 10% within and outwith this region, allaying previous concerns regarding the validity of applying the Galactic conversion ratio to Circinus. The rotation curve, as traced by both the HI and CO, exhibits a steep dip at ~1 kpc, the edge of the atomic/molecular ring, within which the star-burst is occurring. We find the atomic and molecular gases to trace different kinematical features and believe that the fastest part of the sub-kpc ring consists overwhelmingly of molecular gas. Beyond the inner kpc, the velocity climbs to settle into a solid body rotation at >10 kpc. Most of the starlight emanates from within this radius and so much of the dynamical mass, which remains climbing to the limit of our data (>50 kpc), must be due to the dark matter halo.
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