Constraining the assembly time of the stellar haloes of nearby Milky Way-mass galaxies through AGB populations
Constraining the assembly time of the stellar haloes of nearby Milky Way-mass galaxies through AGB populations
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通过 AGB 种群限制邻近银河系质量星系的恒星晕的组装时间
DOI：
10.1093/mnras/stad2480
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发表时间：
2023
影响因子：
4.8
通讯作者：
Holwerda, Benne W.
中科院分区：
文献类型：
--
作者：
Harmsen, Benjamin;Bell, Eric F.;D’Souza, Richard;Monachesi, Antonela;de Jong, Roelof S.;Smercina, Adam;Jang, In Sung;Holwerda, Benne W.
星系恒星晕的恒星形成历史（SFHs）为星系的合并历史以及这些合并对其宿主的影响提供了至关重要的见解。这些测量表明，虽然银河系最重要的合并发生在8-10 Gyr之前，但M31最大的合并发生在最近的几个Gyr内。不幸的是，所需的光晕SFH测量在本群之外是非常昂贵的。在这里，我们使用比红巨星分支（RGB）尖端更亮的渐近巨星分支（AGB）恒星来约束恒星晕SFHs。恒星群模型和档案数据集都表明，AGB/RGB比率限制了90%恒星形成之前的时间。我们在三个高度倾斜的银河系质量星系的光晕中发现了AGB恒星，通过哈勃太空望远镜对恒星进行了分辨率测量；这个星团在NGC 253和NGC 891的恒星晕中最为突出，这表明它们的恒星晕中包含了相对较晚出生的恒星，推断为90 ~ 6±1.5 Gyr。这一比率也因地区而异，沿长轴和潮汐流或贝壳趋向于较高的值。通过将我们的测量结果与先前的约束条件相结合，我们发现了晕年龄和恒星晕质量之间的初步反相关关系，这一趋势存在于星系形成模型中，但以前从未被阐明过，即银河系质量星系中最大的恒星晕是最近才聚集起来的。
The star formation histories (SFHs) of galactic stellar haloes offer crucial insights into the merger history of the galaxy and the effects of those mergers on their hosts. Such measurements have revealed that while the Milky Way’s most important merger was 8–10 Gyr ago, M31’s largest merger was more recent, within the last few Gyr. Unfortunately, the required halo SFH measurements are extremely observationally expensive outside of the Local Group. Here, we use asymptotic giant branch (AGB) stars brighter than the tip of the red giant branch (RGB) to constrain stellar halo SFHs. Both stellar population models and archival data sets show that the AGB/RGB ratio constrains the time before which 90 per cent of the stars formed,t90. We find AGB stars in the haloes of three highly inclined roughly Milky Way-mass galaxies with resolved star measurements from theHubble Space Telescope; this population is most prominent in the stellar haloes of NGC 253 and NGC 891, suggesting that their stellar haloes contain stars born at relatively late times, with inferredt90∼ 6 ± 1.5 Gyr. This ratio also varies from region to region, tending towards higher values along the major axis and in tidal streams or shells. By combining our measurements with previous constraints, we find a tentative anticorrelation between halo age and stellar halo mass, a trend that exists in models of galaxy formation but has never been elucidated before, i.e. the largest stellar haloes of Milky Way-mass galaxies were assembled more recently.