Department of Astronomy, Yale University, New Haven, CT, USA.
Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany.
Nature. 2022 May;605(7910):435-439. doi: 10.1038/s41586-022-04665-6. Epub 2022 May 18.
The ultra-diffuse galaxies DF2 and DF4 in the NGC 1052 group share several unusual properties: they both have large sizes, rich populations of overluminous and large globular clusters, and very low velocity dispersions that indicate little or no dark matter. It has been suggested that these galaxies were formed in the aftermath of high-velocity collisions of gas-rich galaxies, events that resemble the collision that created the bullet cluster but on much smaller scales. The gas separates from the dark matter in the collision and subsequent star formation leads to the formation of one or more dark-matter-free galaxies. Here we show that the present-day line-of-sight distances and radial velocities of DF2 and DF4 are consistent with their joint formation in the aftermath of a single bullet-dwarf collision, around eight billion years ago. Moreover, we find that DF2 and DF4 are part of an apparent linear substructure of seven to eleven large, low-luminosity objects. We propose that these all originated in the same event, forming a trail of dark-matter-free galaxies that is roughly more than two megaparsecs long and angled 7° ± 2° from the line of sight. We also tentatively identify the highly dark-matter-dominated remnants of the two progenitor galaxies that are expected at the leading edges of the trail.
NGC 1052 星系群中的超扩散星系 DF2 和 DF4 具有几个不寻常的性质：它们都具有较大的尺寸、丰富的超亮和大球状星团族群，以及非常低的速度分散度，这表明它们几乎没有或没有暗物质。有人提出，这些星系是在富含气体的星系高速碰撞的余波中形成的，这种事件类似于创造子弹星系团的碰撞，但规模要小得多。在碰撞中，气体与暗物质分离，随后的恒星形成导致一个或多个无暗物质星系的形成。在这里，我们表明，DF2 和 DF4 的当前视向距离和径向速度与其在大约 80 亿年前的一次单一子弹矮星系碰撞后的共同形成是一致的。此外，我们发现 DF2 和 DF4 是一个由七个到十一个大的低亮度物体组成的明显线性亚结构的一部分。我们提出，这些物体都起源于同一事件，形成了一条无暗物质星系的轨迹，其长度大致超过两百万秒差距，相对于视线的角度为 7°±2°。我们还暂时确定了在轨迹前缘预计会出现的两个前体星系的高度暗物质主导残余物。
