NGC1052-DF2和NGC1052-DF4中的潮汐畸变：缺乏暗物质的独立证据
Tidal Distortions in NGC1052-DF2 and NGC1052-DF4: Independent Evidence for a Lack of Dark Matter
摘要：
同一星系群中的两个超弥散星系，NGC 1052-DF 2和NGC 1052-DF 4，被发现几乎没有或没有暗物质，并且拥有异常明亮的球状星团。在群体环境中，这种低质量的扩散物体很容易被破坏，预计会显示出潮汐扭曲的证据。在这项工作中，我们提出了深入的新成像的NGC 1052组，获得与蜻蜓长焦阵列，以测试这一假设。我们发现，这两个星系都显示出强烈的位置角扭曲，并显着延长在其郊区比在其内部。星系群中央的巨大椭圆形星系NGC 1052最有可能是这些潮汐扰动的来源。观察到的扭曲意味着星系的总质量很低，或者非常接近NGC 1052。考虑到星系相对距离的限制，我们推断这些星系的暗物质晕质量不可能比它们的恒星质量大得多。从畸变计算近心，我们发现星系是在高度椭圆轨道上，近心与现今半径的比值R 0/R 0 ~0.1，如果星系是无暗物质的，R 0/R 0 ~0.01，如果它们有正常的暗晕。我们的发现提供了强有力的证据，独立于运动学的限制，这两个星系是暗物质缺乏。此外，NGC 1052-DF 2和NGC 1052-DF 4潮汐特征的相似性强烈表明它们产生于与NGC 1052相当的距离。在附录A中，我们描述了sbcontrast，这是一种确定图像表面亮度极限的鲁棒方法。
英文摘要：
Two ultra diffuse galaxies in the same group, NGC1052-DF2 and NGC1052-DF4, have been found to have little or no dark matter and to host unusually luminous globular cluster populations. Such low mass diffuse objects in a group environment are easily disrupted and are expected to show evidence of tidal distortions. In this work we present deep new imaging of the NGC1052 group, obtained with the Dragonfly Telephoto Array, to test this hypothesis. We find that both galaxies show strong position angle twists and are significantly more elongated at their outskirts than in their interiors. The group's central massive elliptical NGC1052 is the most likely source of these tidal disturbances. The observed distortions imply that the galaxies have a low total mass or are very close to NGC1052. Considering constraints on the galaxies' relative distances, we infer that the dark matter halo masses of these galaxies cannot be much greater than their stellar masses. Calculating pericenters from the distortions, we find that the galaxies are on highly elliptical orbits, with a ratio of pericenter to present-day radius Rperi/R0~0.1 if the galaxies are dark matter-free and Rperi/R0~0.01 if they have a normal dark halo. Our findings provide strong evidence, independent of kinematic constraints, that both galaxies are dark matter deficient. Furthermore, the similarity of the tidal features in NGC1052-DF2 and NGC1052-DF4 strongly suggests that they arose at comparable distances from NGC1052. In Appendix A, we describe sbcontrast, a robust method to determine the surface brightness limit of images.
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