Molecular cloud shredding in the Galactic Bar
Molecular cloud shredding in the Galactic Bar
复制标题
银河酒吧中的分子云粉碎
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
H. Liszt
中科院分区：
文献类型：
--
作者：
H. Liszt
在银河系中心最里面的区域之外，分子气体的运动学被少数紧凑但异常宽的神秘起源的特征所控制。我们表明，使用以前的数据，有一个家庭的这样的功能，其成员区分形态上的极端垂直延伸，垂直于倾斜的整体气体倾斜面。在空间上分离出这些特征后，我们以不同程度的完整性以高分辨率（1“）在12 CO、13 CO和CS线上绘制了它们。 虽然在一些单独的光束中存在非常宽的轮廓，但更一般地，我们将运动学分解为空间梯度，该空间梯度先前在更宽的光束中被涂抹以形成更宽的线。最大的视速度梯度通常是相对于银河系纬度，但运动被限制在银河系终端速度内的速度范围内，这表明它是银河系的引力势，这是被挖掘，以创建所观察到的kinematics.
We解释了广泛的功能定性在最近的流体动力学模型的气体流动在强棒星系：在气体进入银河系尘埃带的地方发生的持续激波可以解释在分子气体实际参与这一过程的地方，在小空间体积上出现宽线的原因。要解释的动态序列的复杂行为内看到的宽线功能，我们讨论如何太阳必须定向相对于酒吧。在这样做的过程中，我们确定了在其他星系中看到的具有巨大H II区Sgr A，B，C等复合体的核恒星形成环。并且表明，对于半径为175秒差距（太阳中心距离为8.5千秒差距）的环，运动学与预期的一样，旋转速度约为210 km s-1。气体在$l=0$°（著名的“膨胀分子环”）附近有清晰而强烈的向外非圆周运动 ，然后与进入尘埃带内端的气体“喷雾”相关联，为酒吧定义了一个更接近端部的视角。
使用推断的几何形状，我们构建了一个描述这里最完整映射的特征的行为，在$l = 5.4$°，气体基本上福尔斯从天空中落下，并集中在观察到的稠密，明亮的分子核心，然后被撕碎并吸入标称银河系赤道以下100 pc或更多的尘埃带的流入。从那里，它被回收并被提升回更接近赤道的核环区域。当然，这个和其他特征的垂直结构，以及尘埃带和星系内气体层的整体倾斜，都还有待于理论上的讨论。
Seen just outside the innermost regions of the galactic center, the kinematics of molecular gas are dominated by a handful of compact but unusually broad-lined features of enigmatic origin. We show, using previous data, that there is a family of such features whose members are distinguished morphologically by their extreme vertical extension, perpendicular to the inclined plane of the overall gas tilt. Having isolated the features spatially, we mapped them with varying degrees of completeness at high resolution (1´) in lines of 12 CO, 13 CO and CS. Although very broad profiles exist in some individual beams, more generally we resolved the kinematics into spatial gradients which earlier were smeared in broader beams to form wider lines. The largest apparent velocity gradients are typically with respect to galactic latitude but motions are confined to the range of velocities inside the galactic terminal velocity, indicating that it is the galactic gravitational potential which is being tapped to create the observed kinematics.
We interpret the broad-lined features qualitatively in terms of recent hydrodynamical models of gas flow in strongly barred galaxies: standing shocks which occur where gas enters the Galactic dust lane can account for the presence of broad lines over small spatial volumes wherever molecular gas is actually engaged in this process. To interpret the dynamical sequencing of the complex behaviour seen within the broad-line features we discuss how the Sun must be oriented with respect to the bar. In doing so, we identify the nuclear star-forming rings seen in other galaxies with the complex of giant H II regions Sgr A, B, C etc. and show that the kinematics are as expected for a ring of radius 175 pc (for a Sun-center distance of 8.5 kpc) rotating at about 210 km s -1 . Gas having clear and strong outward-directed non-circular motion around $l=0$° (the famous “expanding molecular ring”) is then associated with the “spray” of incoming gas at the inner ends of the dust lane, defining a more nearly end-on viewing angle for the bar.
Using the inferred geometry, we construct a narrative for the behaviour of the feature most completely mapped here, at $l = 5.4$°, whereby gas basically falls out of the sky and is concentrated into the observed dense, bright molecular core before being shredded and sucked into the inflow of the dust lane 100 pc or more below the nominal galactic equator. From there it is recycled and lifted back into the more nearly equatorial region of the nuclear ring. Of course, the vertical structure of this and the other features, and the overall tilt of the dust lane and inner-galaxy gas layer, all remain to be discussed theoretically.