Colliding molecular clouds in head-on galaxy collisions
Colliding molecular clouds in head-on galaxy collisions
复制标题
正面星系碰撞中分子云的碰撞
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
S. Léon
中科院分区：
文献类型：
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作者：
J. Braine;U. Lisenfeld;P. Duc;E. Brinks;V. Charmandaris;S. Léon
我们进一步观测了旋涡星系迎头碰撞中的分子气体，这次是UGC 813 - UGC 816系统中的CO（J = 1 → 0）和CO（J = 2 → 1）谱线。UGC 813/6是第二个已知的正面螺旋碰撞的例子，第一个例子是UGC 12914/5对。在UGC 813和816之间的桥上有强烈的CO辐射，与恒星辐射无关，就像UGC 12914/5一样。来自UGC 813/6桥的CO排放，不算星系本身的排放，至少是整个银河系的排放。富含气体的螺旋星系的碰撞实际上是星系星际介质（ISM）之间的碰撞。我们表明，分子云之间的碰撞，使H2进入桥区。虽然稠密的云被碰撞电离，但它们冷却并很快重新组合，甚至在星系盘分离之前就再次变成分子。由于星云在碰撞后获得了中等速度，它们被留在了分离星系之间的桥梁中。在桥的分子云中，星星的形成效率似乎很低。我们推测，分子云中的前恒星核可能在云碰撞过程中膨胀，从而延缓未来星星的形成。因为这里讨论的ISM-ISM碰撞需要非常小的碰撞参数，所以它们在场螺旋中很少见。然而，在星系团中，这些碰撞应该是从螺旋内部喷射浓缩气体的重要手段。
We present further observations of molecular gas in head-on collisions of spiral galaxies, this time of the CO(J = 1 → 0) and CO(J = 2 → 1) lines in the UGC 813 - UGC 816 system. UGC 813/6 are only the second known example of head-on spiral-spiral collisions, the first example being the UGC 12914/5 pair. Strong CO emission is present in the bridge between UGC 813 and 816, unassociated with stellar emission, just as in UGC 12914/5. The CO emission from the UGC 813/6 bridge, not counting the emission from the galaxies themselves, is at least that of the entire Milky Way. Collisions of gas-rich spirals are really collisions between the interstellar media (ISMs) of the galaxies. We show that collisions between molecular clouds bring H2 into the bridge region. Although the dense clouds are ionized by the collisions, they cool and recombine very quickly and become molecular again even before the galactic disks separate. Because the clouds acquire an intermediate velocity post-collision, they are left in the bridge between the separating galaxies. The star formation efficiency appears low in the molecular clouds in the bridges. We speculate that the pre-stellar cores in the molecular clouds may expand during the cloud collisions, thus retarding future star formation. Because the ISM-ISM collisions discussed here require a very small impact parameter, they are rare among field spirals. In clusters, however, these collisions should be an important means of ejecting enriched gas from the inner parts of spirals.