Hyper Wide Field Imaging of the Local Group Dwarf Irregular Galaxy IC 1613: An Extended Component of Metal-poor Stars
Hyper Wide Field Imaging of the Local Group Dwarf Irregular Galaxy IC 1613: An Extended Component of Metal-poor Stars
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DOI：
10.3847/1538-4357/ab29fb
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发表时间：
2019-05
期刊：
影响因子：
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通讯作者：
R. Pucha;J. Carlin;B. Willman;J. Strader;D. Sand;K. Bechtol;J. Brodie;D. Crnojevi'c;D. Forbes-D.-F
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作者：
R. Pucha;J. Carlin;B. Willman;J. Strader;D. Sand;K. Bechtol;J. Brodie;D. Crnojevi'c;D. Forbes-D.-F
恒星晕为等级结构的形成提供了化石证据。由于晕组装被预测为无标度，低质量星系周围的恒星晕约束的属性，如星星的形成吸积subhalos和矮星系的形成。然而，很少有观测搜索的恒星晕在矮星存在。本文介绍孤立的本星系群矮不规则星系IC 1613（M 108 M）中解析恒星的gi测光。这些Subaru/Hyper Suprime-Cam观测是IC 1613迄今为止最广泛和最深入的。我们测量了年轻的主序星、中老红巨星分支和古老的水平分支星在IC 1613中心12′（2.6 kpc; 2.5半光半径）以外的表面密度分布。所有的种群都延伸到了24′（25.2 kpc; 5个半光半径），在这些外部区域，较老的种群最适合用一个破指数拟合。与早期对IC 1613内部区域敏感的研究相比，我们发现老恒星群的密度随着离中心的距离而显著变陡;我们追踪g波段的有效表面亮度到非常微弱的极限，为1.33.7 mag arcsec−2。相反，年轻恒星的分布在外部区域遵循单一的、浅的指数分布，这表明IC 1613的年轻和年老成分有不同的形成通道。最外层、中龄和老恒星的性质与吸积恒星晕的预期一致，但需要未来的观测和理论工作来明确区分这种情况与其他可能性。
Stellar halos offer fossil evidence for hierarchical structure formation. Since halo assembly is predicted to be scale-free, stellar halos around low-mass galaxies constrain properties such as star formation in the accreted subhalos and the formation of dwarf galaxies. However, few observational searches for stellar halos in dwarfs exist. Here we present gi photometry of resolved stars in isolated Local Group dwarf irregular galaxy IC 1613 (M⋆ ∼ 108 M⊙). These Subaru/Hyper Suprime-Cam observations are the widest and deepest of IC 1613 to date. We measure surface density profiles of young main-sequence, intermediate to old red giant branch, and ancient horizontal branch stars outside of 12′ (∼2.6 kpc; 2.5 half-light radii) from the IC 1613 center. All of the populations extend to ∼24′ (∼5.2 kpc; 5 half-light radii), with the older populations best fit by a broken exponential in these outer regions. Comparison with earlier studies sensitive to IC 1613's inner regions shows that the density of old stellar populations steepens substantially with distance from the center; we trace the g-band effective surface brightness to an extremely faint limit of ∼33.7 mag arcsec−2. Conversely, the distribution of younger stars follows a single, shallow exponential profile in the outer regions, demonstrating different formation channels for the younger and older components of IC 1613. The outermost, intermediate-age and old stars have properties consistent with those expected for accreted stellar halos, though future observational and theoretical work is needed to definitively distinguish this scenario from other possibilities.