A panoptic view of the Taurus molecular cloud I. The cloud dynamics revealed by gas emission and 3D dust

We present a study of the three-dimensional (3D) distribution of interstellar dust derived from stellar extinction observations toward the Taurus molecular cloud (MC) and its relation with the neutral atomic hydrogen (Hi) emission at 21 cm wavelength and the carbon monoxide 12CO and 13CO emission in the J = 1!0 transition. We used the histogram of oriented gradients (HOG) method to match the morphology in a 3D reconstruction of the dust density (3D dust) and the distribution of the gas tracers’ emission. The result of the HOG analysis is a map of the relationship between the distances and radial velocities. The HOG comparison between the 3D dust and the Hi emission indicates a morphological match at the distance of Taurus but an anti-correlation between the dust density and the Hi emission, which uncovers a significant amount of cold Hi within the Taurus MC. The HOG between the 3D dust and 12CO reveals a pattern in radial velocities and distances that is consistent with converging motions of the gas in the Taurus MC, with the near side of the cloud moving at higher velocities and the far side moving at lower velocities. This convergence of flows is likely triggered by the large-scale gas compression caused by the interaction of the Local Bubble and the Per-Tau shell, with Taurus lying at the intersection of the two bubble surfaces.

本研究基于针对金牛座分子云（Taurus molecular cloud, MC）的恒星消光观测，推导得到星际尘埃的三维（3D）分布，并探讨该分布与21厘米波长中性原子氢（Hi）辐射，以及J=1→0跃迁态一氧化碳12CO、13CO辐射之间的关联。本研究采用方向梯度直方图（histogram of oriented gradients, HOG）方法，匹配尘埃密度三维重建（3D尘埃）结果与气体示踪物辐射的分布形态。HOG分析的输出为距离与径向速度的关系分布图。对3D尘埃与Hi辐射的HOG对比分析表明，在金牛座分子云所在的距离处二者形态匹配，但尘埃密度与Hi辐射呈现反相关关系，这一发现揭示了金牛座分子云内部存在大量冷Hi。3D尘埃与12CO的HOG对比则揭示出径向速度与距离的分布模式，该模式与金牛座分子云内气体的汇聚运动相符：云体近侧以更高速度运动，远侧运动速度更低。这类气流汇聚现象大概率由本地泡（Local Bubble）与Per-Tau壳层相互作用引发的大尺度气体压缩所驱动，而金牛座分子云正处于两个泡面的交汇区域。