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arXiv 2109.09770astro-ph.GA
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NGC 5746：一个大质量盘状星系的形成历史

NGC 5746: formation history of a massive disc-dominated galaxy

Marie Martig, Francesca Pinna, Jesús Falcón-Barroso, Dimitri Gadotti, Bernd Husemann, Ivan Minchev, Justus Neumann, Tomás Ruiz-Lara, Glenn van de Ven

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Accepted for publication in MNRAS. 22 pages, 21 figures (including appendix)
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摘要：

缺乏经典核球的大质量星系的存在经常被认为是对$Λ$ CDM的挑战。然而，最近的模拟表明，一小部分大质量盘星系可能有非常平静的合并历史，而且合并不一定会形成经典的凸起。我们用MUSE对NGC 5746的观测来验证这些想法，NGC 5746是一个大质量的（$\sim 10^{11}$ M $_\odot$）边缘盘星系，没有经典的凸起。我们分析了它的恒星运动学和恒星星族，并推断一个巨大的和扩展的盘形成非常早：80%的星系的恒星质量形成超过10 Gyr前。大部分厚盘和砂杆形成于该早期阶段。棒将气体推向中心，并引发核盘的形成，随后是四方形/花生形凸起的生长。大约在$\sim$ 8 Gyr前，发生了一次$\sim$ 1：10的合并，可能是在低倾角轨道上。卫星没有造成显着的垂直加热，没有贡献的增长，一个经典的隆起，并没有破坏酒吧和核盘。然而，这对银河系来说是一个重要的事件：通过在整个星系中沉积恒星，它为厚盘贡献了$\sim 30$ %的吸积恒星。因此NGC 5746并没有完全逃脱合并，但唯一一次相对较近的重大合并并没有破坏星系，也没有产生经典的隆起。未来的观测将揭示这是否代表了大质量盘状星系的形成历史。

英文摘要：

The existence of massive galaxies lacking a classical bulge has often been proposed as a challenge to $Λ$CDM. However, recent simulations propose that a fraction of massive disc galaxies might have had very quiescent merger histories, and also that mergers do not necessarily build classical bulges. We test these ideas with deep MUSE observations of NGC 5746, a massive ($\sim 10^{11}$ M$_\odot$) edge-on disc galaxy with no classical bulge. We analyse its stellar kinematics and stellar populations, and infer that a massive and extended disc formed very early: 80% of the galaxy's stellar mass formed more than 10 Gyr ago. Most of the thick disc and the bar formed during that early phase. The bar drove gas towards the center and triggered the formation of the nuclear disc followed by the growth of a boxy/peanut-shaped bulge. Around $\sim$ 8 Gyr ago, a $\sim$1:10 merger happened, possibly on a low-inclination orbit. The satellite did not cause significant vertical heating, did not contribute to the growth of a classical bulge, and did not destroy the bar and the nuclear disc. It was however an important event for the galaxy: by depositing its stars throughout the whole galaxy it contributed $\sim 30$% of accreted stars to the thick disc. NGC 5746 thus did not completely escape mergers, but the only relatively recent significant merger did not damage the galaxy and did not create a classical bulge. Future observations will reveal if this is representative of the formation histories of massive disc galaxies.

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