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Is Fornax 4 the nuclear star cluster of the Fornax dwarf spheroidal galaxy?
Monthly Notices of the Royal Astronomical Society ( IF 4.8 ) Pub Date : 2020-06-03 , DOI: 10.1093/mnras/staa1482 S Martocchia 1, 2 , E Dalessandro 3 , M Salaris 2 , S Larsen 4 , M Rejkuba 1
Monthly Notices of the Royal Astronomical Society ( IF 4.8 ) Pub Date : 2020-06-03 , DOI: 10.1093/mnras/staa1482 S Martocchia 1, 2 , E Dalessandro 3 , M Salaris 2 , S Larsen 4 , M Rejkuba 1
Affiliation
Fornax 4 is the most distinctive globular cluster in the Fornax dwarf spheroidal. Located close to the centre of the galaxy, more metal-rich and potentially younger than its four companions (namely, Fornax clusters number 1, 2, 3 and 5), it has been suggested to have experienced a different formation than the other clusters in the galaxy. Here we use HST/WFC3 photometry to characterize the stellar population content of this system and shed new light on its nature. By means of a detailed comparison of synthetic horizontal branch and red giant branch with the observed colour-magnitude diagrams, we find that this system likely hosts stellar sub-populations characterized by a significant iron spread up to $\Delta$[Fe/H]$\sim$0.4 dex and possibly by also some degree of He abundance variations $\Delta$Y$\sim0.03$. We argue that this purely observational evidence, combined with the other peculiarities characterizing this system, supports the possibility that Fornax 4 is the nuclear star cluster of the Fornax dwarf spheroidal galaxy. A spectroscopic follow-up for a large number of resolved member stars is needed to confirm this interesting result and to study in detail the formation and early evolution of this system and more in general the process of galaxy nucleation.
中文翻译:
Fornax 4 是 Fornax 矮椭球星系的核星团吗?
Fornax 4 是 Fornax 矮球体中最独特的球状星团。位于星系中心附近,金属含量更高,可能比它的四个伴星(即天炉星团 1、2、3 和 5)更年轻,有人认为它经历了与其他星团不同的形成银河系。在这里,我们使用 HST/WFC3 光度法来表征该系统的恒星种群含量,并对其性质进行了新的解释。通过将合成水平分支和红巨星分支与观察到的颜色-星等图进行详细比较,我们发现该系统可能拥有以高达 $\Delta$[Fe/H] 的显着铁扩散为特征的恒星亚群$\sim$0.4 dex 和可能还有一定程度的 He 丰度变化 $\Delta$Y$\sim0.03$。我们认为,这一纯粹的观察证据,结合表征该系统的其他特性,支持了 Fornax 4 是 Fornax 矮椭球星系的核星团的可能性。需要对大量已解析的成员恒星进行光谱跟踪,以确认这一有趣的结果,并详细研究该系统的形成和早期演化,以及更一般的星系成核过程。
更新日期:2020-06-03
中文翻译:
Fornax 4 是 Fornax 矮椭球星系的核星团吗?
Fornax 4 是 Fornax 矮球体中最独特的球状星团。位于星系中心附近,金属含量更高,可能比它的四个伴星(即天炉星团 1、2、3 和 5)更年轻,有人认为它经历了与其他星团不同的形成银河系。在这里,我们使用 HST/WFC3 光度法来表征该系统的恒星种群含量,并对其性质进行了新的解释。通过将合成水平分支和红巨星分支与观察到的颜色-星等图进行详细比较,我们发现该系统可能拥有以高达 $\Delta$[Fe/H] 的显着铁扩散为特征的恒星亚群$\sim$0.4 dex 和可能还有一定程度的 He 丰度变化 $\Delta$Y$\sim0.03$。我们认为,这一纯粹的观察证据,结合表征该系统的其他特性,支持了 Fornax 4 是 Fornax 矮椭球星系的核星团的可能性。需要对大量已解析的成员恒星进行光谱跟踪,以确认这一有趣的结果,并详细研究该系统的形成和早期演化,以及更一般的星系成核过程。