孤立宿主星系周围 MATLAS 与 ELVES 矮卫星系统的不对称分布
Lopsided distribution of MATLAS and ELVES dwarf satellite systems around isolated host galaxies
AI总结：
本文利用六种度量研究 MATLAS 和 ELVES 巡天中孤立宿主星系周围矮卫星系统的不对称分布，发现约 16%–21% 的系统显著不对称，且远距离卫星和红色早型宿主贡献更大，为与宇宙学模拟比较提供了观测基准。
摘要：
卫星矮星系的性质为在星系尺度上验证宇宙学模型提供了重要的经验约束。特别是它们的相空间相关性，为各种模型提供了有趣的见解。除了卫星平面现象之外，卫星相对于其宿主星系的不对称分布也已在观测和宇宙学模拟中得到研究。目前仍不清楚观测到的不对称性与模拟预期之间的一致性如何。我们使用六种不同的度量指标来测量观测到的孤立卫星系统中的不对称性。我们研究了来自 MATLAS 巡天、位于本星系体积（Local Volume, LV）之外的 47 个系统，以及来自 ELVES 巡天的 21 个 LV 卫星系统。我们发现，所谓的楔形度量——即统计具有不同张角的楔形区域内矮星系的数目——最适合刻画系统整体的不对称性。在该度量下，我们的分析揭示，与具有随机生成的卫星位置角的系统相比，约 16% 的被测卫星系统表现出统计显著的不对称程度。这相对于在没有整体固有不对称性的样本中预期的 5%（2 sigma 水平）显著不对称系统比例，呈现出明显的超出。然而，使用多种度量能够提供更完整的图景。综合所有被测度量，显著不对称系统的数量增加到约 21%。与文献中最近的结果相反，我们发现 MATLAS 巡天中的红色早型星系比 ELVES 中主要为蓝色的晚型宿主星系具有更多的不对称系统。我们进一步发现，距离宿主更远的卫星星系——可能是最近吸积的——很可能是所报告的不对称性超出的主要贡献者。我们的结果使得能够与模拟中的类似系统进行比较，以评估其与标准模型的一致性。
英文摘要：
The properties of satellite dwarf galaxies pose important empirical constraints to verify cosmological models on galaxy scales. Their phase-space correlations, in particular, offer interesting insights into various models. Next to the planes-of-satellites phenomenon, the lopsided distribution of satellites relative to their host galaxy has been studied observationally and in cosmological simulations. It is still unclear how observed lopsidedness aligns with expectations from simulations. We measure lopsidedness in observed isolated satellite systems using six different metrics. We study 47 systems from the MATLAS survey beyond the Local Volume (LV) as well as 21 LV satellite systems from the ELVES survey. We find that the so-called wedge metric, counting the number of dwarfs in wedges with varying opening angles, is best suited to capture a system's overall lopsidedness. Under this metric, our analysis reveals that ~16 percent of the tested satellite systems exhibit a statistically significant degree of lopsidedness when compared to systems with randomly generated satellite position angles. This presents a notable excess over the expected 5% (2 sigma level) of significantly lopsided systems in a sample with no overall inherent lopsidedness. However, using multiple metrics provides a more complete picture. Combining all tested metrics, the number of significantly lopsided systems increases to ~21 percent. Contrary to recent results from the literature, we find more lopsided systems among the red early-type galaxies in the MATLAS survey compared to the mostly blue late-type hosts in ELVES. We further find that satellite galaxies at larger distances from the host, potentially recently accreted, are likely the primary contributors to the reported excess of lopsidedness. Our results enable comparisons with similar systems in simulations to assess consistency with the standard model.
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