标题： 致密椭圆星系的形成路径 显示英文标题

标题： The formation pathways of compact elliptical galaxies

摘要： 紧凑椭圆星系（cE）仍然是一个难以研究的星系类别。最近的观测表明孤立的和与宿主相关的cE星系具有不同的形成路径，而模拟研究表明不同的路径也可以导致cE星系的形成。然而，尚未建立坚实的相关性，每种路径在宇宙学背景下的相对贡献仍然未知。在这里，我们结合了来自SAMI星系巡天的空间分辨cE星系样本和IllustrisTNG宇宙学模拟中的匹配星系样本，以全面了解这些星系是如何形成的。观测到的靠近宿主星系的cE星系看起来比孤立的cE星系更红、更小且年龄更大，这支持了先前关于多种形成路径的证据。追溯模拟中的cE星系，我们发现了两种主要的形成路径：32$\pm$5%的星系通过螺旋星系被更大的宿主星系剥离形成，而68$\pm$4%的星系通过孤立环境中恒星质量的逐渐积累形成。我们证实不同环境中的cE星系确实通过不同的路径形成，样本中的所有孤立cE星系均通过原位形成（即没有从之前的宿主星系中弹出），并且77$\pm$6%的与宿主相关的cE星系通过潮汐剥离形成。根据它们的形成路径将它们分开后，我们能够重现孤立和与宿主相关的cE星系之间的观测差异，表明这些差异可以通过主导每个环境的不同形成路径完全解释。 显示英文摘要

摘要： Compact elliptical (cE) galaxies remain an elusively difficult galaxy class to study. Recent observations have suggested that isolated and host-associated cEs have different formation pathways, while simulation studies have also shown different pathways can lead to a cE galaxy. However a solid link has not been established, and the relative contributions of each pathway in a cosmological context remains unknown. Here we combine a spatially-resolved observational sample of cEs taken from the SAMI galaxy survey with a matched sample of galaxies within the IllustrisTNG cosmological simulation to establish an overall picture of how these galaxies form. The observed cEs located near a host galaxy appear redder, smaller and older than isolated cEs, supporting previous evidence for multiple formation pathways. Tracing the simulated cEs back through time, we find two main formation pathways; 32 $\pm$ 5 percent formed via the stripping of a spiral galaxy by a larger host galaxy, while 68 $\pm$ 4 percent formed through a gradual build-up of stellar mass in isolated environments. We confirm that cEs in different environments do indeed form via different pathways, with all isolated cEs in our sample having formed via in-situ formation (i.e. none were ejected from a previous host), and 77 $\pm$ 6 percent of host-associated cEs having formed via tidal stripping. Separating them by their formation pathway, we are able to reproduce the observed differences between isolated and host-associated cEs, showing that these differences can be fully explained by the different formation pathways dominating in each environment.