Galactic outflows driven by stellar feedback are crucial for explaining the inefficiency of star formation in galaxies. Although strong feedback can promote the formation of galactic discs by limiting star formation at early times and removing low angular momentum gas, it is not understood how the same feedback can result in diverse objects such as elliptical galaxies or razor thin spiral galaxies. We investigate this problem using cosmological zoom-in simulations of two galaxies forming within $10^{12}~\mathrm{M_\odot}$ halos with almost identical mass accretion histories and halo spin parameters. However, the two resulting galaxies end up with very different bulge-to-disc ratios at $z = 0$. At $z>1.5$, the two galaxies feature a surface density of star formation $\Sigma_{\rm SFR}\simeq 10~\mathrm{M_\odot}~{\rm yr}^{-1}~{\rm kpc}^{-2}$, leading to strong outflows. After the last starburst episode, both galaxies feature a dramatic gaseous disc growth from 1~kpc to 5~kpc during 1~Gyr, a decisive event we dub "the Grand Twirl". After this event, the evolutionary tracks diverge strongly, with one galaxy ending up as a bulge-dominated galaxy, whereas the other ends up as a disc-dominated galaxy. The origins of this dichotomy are the angular momentum of the accreted gas, and whether it adds constructively to the initial disc angular momentum. The build-up of this extended disc leads to a rapid lowering of $\Sigma_{\rm SFR}$ by over two orders of magnitude with $\Sigma_{\rm SFR} \lesssim 0.1~\mathrm{M_\odot}~{\rm yr}^{-1}~{\rm kpc}^{-2}$, in remarkable agreement with what is derived from Milky Way stellar populations. As a consequence, supernovae explosions are spread out and cannot launch galactic outflows anymore, allowing for the persistence of a thin, gently star forming, extended disc.

中文翻译：

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作为扩展的薄盘的起源的快速丝状增生

由恒星反馈驱动的星系外流对于解释星系中恒星形成的低效率至关重要。尽管强反馈可以通过在早期限制恒星形成和去除低角动量气体来促进星系盘的形成，但尚不清楚相同的反馈如何导致不同的物体，如椭圆星系或剃刀细螺旋星系。我们使用在 $10^{12}~\mathrm{M_\odot}$ 晕圈内形成的两个星系的宇宙学放大模拟来研究这个问题，该晕圈具有几乎相同的质量吸积历史和晕圈自旋参数。然而，两个由此产生的星系最终在 $z = 0$ 处具有非常不同的凸出盘比。在 $z>1.5$ 处，两个星系的表面密度为恒星形成 $\Sigma_{\rm SFR}\simeq 10~\mathrm{M_\odot}~{\rm yr}^{-1}~{\ rm kpc}^{-2}$, 导致大量流出。在最后一次星爆事件之后，两个星系都在 1~Gyr 期间出现了从 1~kpc 到 5~kpc 的戏剧性气体盘生长，我们将这一决定性事件称为“大旋转”。在此事件之后，演化轨迹出现强烈分歧，一个星系最终成为一个以凸起为主的星系，而另一个最终成为一个以圆盘为主的星系。这种二分法的起源是吸积气体的角动量，以及它是否建设性地增加了初始盘角动量。这个扩展圆盘的形成导致 $\Sigma_{\rm SFR}$ 快速降低超过两个数量级，$\Sigma_{\rm SFR} \lesssim 0.1~\mathrm{M_\odot}~ {\rm yr}^{-1}~{\rm kpc}^{-2}$，与来自银河系恒星群的数据非常一致。作为结果，