合并星系群RXJ0751 .3+5012中的弓形激波、冷锋和冷核解体
The bow shock, cold fronts and disintegrating cool core in the merging galaxy group RXJ0751.3+5012
摘要：
本文报道了对离轴星系团合并RXJ0751.3+5012的Chandra X射线观测。两个碰撞星系团的炽热大气层因合并而显得高度扭曲。这些图像揭示了每个群核心周围的弧形冷锋，由通过周围介质的运动产生，以及第一次检测到群合并冲击波阵面。我们探测到一个明显的密度和温度跃变，它与北群前面的一个马赫数M=1.9+/-0.4的弓形激波有关。利用星系红移和1100+/-300 km/s的激波速度，我们估计合并轴距离天空平面只有10度。从90千秒差距的预测群间隔来看，这对应于距离最近点0.1 Gyr的时间。北群拥有一个致密、凉爽的核心，有一个延伸100千秒差距的冲压压力剥离的气体尾部。这条尾巴被剪切的侧面由于开尔文-亥姆霍兹不稳定性而显得扭曲和加宽。我们使用这种子结构的存在下放置的磁场强度的上限，并为斯皮策式粘度，表明这些结构的发展是一致的临界扰动长度以上的不稳定性可以在组内介质中生长。北星系群的核心还拥有一对星系UGC 4052，周围有一个直径为40 kpc的红外和近紫外环。这个环可能是由UGC 4052对一个较小星系的潮汐剥离产生的，也可能是两个大星系近距离相遇产生的碰撞环。
英文摘要：
We present a new Chandra X-ray observation of the off-axis galaxy group merger RXJ0751.3+5012. The hot atmospheres of the two colliding groups appear highly distorted by the merger. The images reveal arc-like cold fronts around each group core, produced by the motion through the ambient medium, and the first detection of a group merger shock front. We detect a clear density and temperature jump associated with a bow shock of Mach number M=1.9+/-0.4 ahead of the northern group. Using galaxy redshifts and the shock velocity of 1100+/-300 km/s, we estimate that the merger axis is only 10deg from the plane of the sky. From the projected group separation of 90 kpc, this corresponds to a time since closest approach of 0.1 Gyr. The northern group hosts a dense, cool core with a ram pressure stripped tail of gas extending 100 kpc. The sheared sides of this tail appear distorted and broadened by Kelvin-Helmholtz instabilities. We use the presence of this substructure to place an upper limit on the magnetic field strength and, for Spitzer-like viscosity, show that the development of these structures is consistent with the critical perturbation length above which instabilities can grow in the intragroup medium. The northern group core also hosts a galaxy pair, UGC4052, with a surrounding IR and near-UV ring 40 kpc in diameter. The ring may have been produced by tidal stripping of a smaller galaxy by UGC4052 or it may be a collisional ring generated by a close encounter between the two large galaxies.
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