The Saga of M81: Global View of a Massive Stellar Halo in Formation
The Saga of M81: Global View of a Massive Stellar Halo in Formation
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DOI：
10.3847/1538-4357/abc485
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发表时间：
2019-10
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影响因子：
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通讯作者：
A. Smercina;E. Bell;P. Price;C. Slater;R. D’Souza;J. Bailin;R. D. de Jong;I. Jang;A. Monachesi;D. Nidever
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作者：
A. Smercina;E. Bell;P. Price;C. Slater;R. D’Souza;J. Bailin;R. D. de Jong;I. Jang;A. Monachesi;D. Nidever
最近的研究表明，银河系质量的星系显示出令人难以置信的恒星晕特性，但这种多样性的起源尚不清楚。附近的星系M81-目前正在与M82和NGC 3077相互作用-为这个问题提供了独特的光线。我们提出了一个斯巴鲁超级Suprime-Cam调查解决恒星人口周围的M81，揭示了M81的恒星晕在前所未有的细节。我们将晕解析为前所未有的V波段等效表面亮度33 mag arcsec −2，并制作了有史以来第一张本星系群外银河系质量恒星晕的全球恒星质量密度图。利用短轴，我们确认M81的晕是已知质量最低、金属含量最少的晕之一（M = 1.16 × 109 M，[Fe/H]=-1.2），这表明它有一个相对平静的吸积历史。然而，我们的全球晕普查发现，来自M82和NGC 3077的潮汐非结合物质提供了大量富含金属的物质（M = 5.4 × 108 M，[Fe/H]=-0.9）。我们进一步表明，在它的大质量卫星M82（以及类似LMC的NGC 3077）吸积之后，M81将拥有附近宇宙中最大质量和最富含金属的恒星晕之一。因此，M81的佐贺：在经历了一段被动的历史之后，M81与M82的合并将彻底改变它的光环，从一个与银河系相媲美的低质量、贫血的光环，变成一个富含金属的庞然大物，只有像M31这样的系统才能与之匹敌。这种戏剧性的转变表明，观察到的恒星晕特性的多样性主要是由这些星系经历的最大合并的多样性驱动的。
Recent work has shown that Milky Way–mass galaxies display an incredible range of stellar halo properties, yet the origin of this diversity is unclear. The nearby galaxy M81—currently interacting with M82 and NGC 3077—sheds unique light on this problem. We present a Subaru Hyper Suprime-Cam survey of the resolved stellar populations around M81, revealing M81's stellar halo in never-before-seen detail. We resolve the halo to unprecedented V-band equivalent surface brightnesses of 33 mag arcsec −2 and produce the first-ever global stellar mass density map for a Milky Way–mass stellar halo outside of the Local Group. Using the minor axis, we confirm M81's halo as one of the lowest mass and metal poorest known (M⋆ ≃ 1.16 × 109M⊙, [Fe/H] ≃ −1.2)—indicating a relatively quiet prior accretion history. Yet, our global halo census finds that tidally unbound material from M82 and NGC 3077 provides a substantial infusion of metal-rich material (M⋆ ≃ 5.4 × 108 M⊙, [Fe/H] ≃−0.9). We further show that, following the accretion of its massive satellite M82 (and the LMC-like NGC 3077), M81 will host one of the most massive and metal-rich stellar halos in the nearby universe. Thus, the saga of M81: following a passive history, M81's merger with M82 will completely transform its halo from a low-mass, anemic halo rivaling the Milky Way, to a metal-rich behemoth rivaled only by systems such as M31. This dramatic transformation indicates that the observed diversity in stellar halo properties is primarily driven by diversity in the largest mergers these galaxies have experienced.