发表机构
Université de Strasbourg, CNRS, Observatoire astronomique de Strasbourg; Centre National d’Etudes Spatiales – Centre spatial de Toulouse; Institute for Astronomy, University of Edinburgh; Observatoire de Paris, PSL Research University; INAF-Osservatorio Astronomico di Capodimonte; Max-Planck-Institut für Astronomie; Institut UTINAM, Observatoire de Besançon（斯特拉斯堡大学，法国国家科学研究中心，斯特拉斯堡天文台; 法国国家空间研究中心 - 图卢兹航天中心; 爱丁堡大学天体物理研究所; 巴黎天文台，PSL研究大学; 意大利国家天体物理研究所卡波迪蒙特天文台; 马克斯·普朗克天文学研究所; UTINAM研究所，贝桑松天文台）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文报告在Euclid DR1中发现Fornax-7，一个位于Fornax矮椭球星系附近的超微弱恒星系统，通过前向建模估计其年龄约10.4吉年、质量约170太阳质量，可能为遥远星团、矮卫星或独立超微弱卫星，需后续观测确认。
AI 中文摘要
我们报告在Euclid DR1中于Fornax矮椭球（dSph）星系附近发现了一个超微弱恒星系统。该系统被命名为Fornax-7，位于距Fornax dSph中心1.1度处，距离约145千秒差距，假设Fornax dSph的距离，对应的投影距离约为2.8千秒差距。我们利用其颜色-星等图（CMD）、光度函数（LF）以及来自地面数据的集成光学颜色来刻画Fornax-7的特征。这些观测量通过一个前向建模框架联合建模，以约束其距离模数、恒星种群属性和总恒星质量。假设低金属丰度为-2.2 ≤ [M/H] ≤ -2.0，类似于已知的银河系和LMC周围的超微弱系统，我们推导出的距离模数与Fornax dSph一致。我们估计其年龄为（10.4±1.9）吉年，并推断其恒星质量为170^{+50}_{-62}太阳质量。放宽金属丰度约束，允许覆盖已知古老Fornax球状星团（GCs）金属丰度的更宽范围，我们发现一个贫金属种群，但金属丰度更高，[M/H]=-1.4±0.3，而年龄、距离模数和质量基本保持不变。这些结果表明其可能与Fornax dSph存在物理关联。Fornax-7可能代表与Fornax相关的极遥远星团、Fornax的矮卫星（即“卫星的卫星”），或银河系外晕中独立的超微弱卫星。在所有情况下，它都是一个特殊的系统，探测了星系和星团形成的最低质量区间，以及矮星系晕的结构。需要更深的测光和光谱后续观测来确认该系统的性质及其与Fornax的动力学联系。
英文摘要
We report the discovery of an ultra-faint stellar system in the vicinity of the Fornax dwarf spheroidal (dSph) galaxy in Euclid DR1. This system, which we designate Fornax-7, is located $1.1$ deg from the centre of the Fornax dSph at about $145$ kpc, corresponding to a projected distance of $\sim 2.8$ kpc assuming the distance of the Fornax dSph. We characterise Fornax-7 using constraints from its colour-magnitude diagram (CMD), luminosity function (LF), and integrated optical colours from ground-based data. These observables are modelled jointly through a forward-modelling framework to constrain its distance modulus, stellar population properties, and total stellar mass. Assuming a low metallicity of $-2.2 \leq {\rm [M/H]} \leq -2.0$, similar to known ultra-faint systems around the Milky Way and the LMC, we derive a distance modulus consistent with that of the Fornax dSph. We estimate an age of $(10.4\pm1.9)$ Gyr and infer a stellar mass of $170^{+50}_{-62}$ solar masses. Relaxing the metallicity constraint and allowing for a wider range that covers the metallicity of the known old Fornax globular clusters (GCs), we find a metal-poor population but with a higher metallicity ${\rm [M/H]}=-1.4\pm0.3$, while the age, distance modulus, and mass remain mostly the same. These results suggest a likely physical association with the Fornax dSph. Fornax-7 may represent either an extremely remote star cluster associated with Fornax, a dwarf satellite of Fornax (i.e., a "satellite of a satellite"), or an independent ultra-faint satellite in the outer halo of the Milky Way. In all cases, it constitutes an exceptional system probing the lowest-mass regime of galaxy and star cluster formation, and the structure of dwarf galaxy haloes. Deeper photometric and spectroscopic follow-up observations are required to confirm both the nature of the system and its dynamical connection to Fornax.
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