室女座壮观的H $α$复合体：M86和NGC 4438碰撞的证据和椭圆星系碰撞ISM加热的意义
A Spectacular H$α$ Complex in Virgo: Evidence for a Collision Between M86 and NGC 4438 and Implications for Collisional ISM Heating of Ellipticals
摘要：
室女星系团巨椭圆星系M86周围的深宽场H $α$ +[NII]成像揭示了一个高度复杂和扰动的ISM/ICM。最引人注目的特征是一组H $α$细丝，它清楚地将M86与附近的扰动螺旋星系NGC 4438（23 $'$ = 120 kpc的投影距离）连接起来，为它们之间先前未被认识的碰撞提供了强有力的证据。选定区域的光谱显示，M86和NGC 4438之间的速度梯度相当平滑，与碰撞情景一致。这样的碰撞会给M86的ISM带来巨大的能量，可能会加热气体并阻止气体冷却形成恒星。我们认为，冷气体剥离从NGC 4438在碰撞过程中，并在其尾流沉积被加热的冲击，冲压压力阻力，或热传导，产生大多数的H $α$丝。一些H $α$细丝与核西北方向的明亮X射线辐射脊有关，这表明碰撞是M86先前归因于其他效应的特殊性的原因。M86是无线电宁静的，因此活动星系核加热不太可能扮演重要角色。M86系统对于理解引力相互作用在椭圆星系ISM加热中的作用以及星系团中的碰撞如何改变星系具有重要意义。
英文摘要：
Deep wide-field H$α$+[NII] imaging around the Virgo cluster giant elliptical galaxy M86 reveals a highly complex and disturbed ISM/ICM. The most striking feature is a set of H$α$ filaments which clearly connect M86 with the nearby disturbed spiral NGC 4438 (23$'$=120 kpc projected away), providing strong evidence for a previously unrecognized collision between them. Spectroscopy of selected regions show a fairly smooth velocity gradient between M86 and NGC 4438, consistent with the collision scenario. Such a collision would impart significant energy into the ISM of M86, probably heating the gas and acting to prevent the gas from cooling to form stars. We propose that cool gas stripped from NGC 4438 during the collision and deposited in its wake is heated by shocks, ram pressure drag, or thermal conduction, producing most of the H$α$ filaments. Some H$α$ filaments are associated with the well-known ridge of bright X-ray emission to the NW of the nucleus, suggesting that the collision is responsible for peculiarities of M86 previously ascribed to other effects. M86 is radio-quiet, thus AGN heating is unlikely to play a significant role. The M86 system has implications for understanding the role of gravitational interactions in the heating of the ISM in ellipticals, and how collisions in clusters transform galaxies.
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