A key feature of a large population of low-mass, late-type disc galaxies are star-forming discs with exponential light distributions. They are typically also associated with thin and flat morphologies, blue colours, and dynamically cold stars moving along circular orbits within co-planar thin gas discs. However, the latter features do not necessarily always imply the former, in fact, a variety of different kinematic configurations do exist. In this work, we use the cosmological hydrodynamical IllustrisTNG simulation to study the nature and origin of dynamically hot, sometimes even counter-rotating, star-forming disc galaxies in the lower stellar mass range (between $5\times 10^9\, \mathrm{M_{\odot }}$ and $2\times 10^{10}\, \mathrm{M_{\odot }}$). We find that being dynamically hot arises in most cases as an induced transient state, for example due to galaxy interactions and merger activities, rather than as an age-dependent evolutionary phase of star-forming disc galaxies. The dynamically hot but still actively star-forming discs show a common feature of hosting kinematically misaligned gas and stellar discs, and centrally concentrated on-going star formation. The former is often accompanied by disturbed gas morphologies, while the latter is reflected in low gas and stellar spins in comparison to their dynamically cold, normal disc counterparts. Interestingly, observed galaxies from MaNGA with kinematic misalignment between gas and stars show remarkably similar general properties as the IllustrisTNG galaxies, and therefore are plausible real-world counterparts. In turn, this allows us to make predictions for the stellar orbits and gas properties of these misaligned galaxies.

中文翻译：

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IllustrisTNG 中的热和反向旋转的恒星形成圆盘星系及其现实世界的对应物

大量低质量、晚期型圆盘星系的一个关键特征是具有指数光分布的恒星形成圆盘。它们通常还与薄而扁平的形态、蓝色以及在共面薄气体盘内沿圆形轨道移动的动态冷恒星有关。然而，后者的特征并不一定总是暗示前者，事实上，确实存在各种不同的运动学配置。在这项工作中，我们使用宇宙学流体动力学 IllustrisTNG 模拟来研究在较低恒星质量范围内（在 $5\times 10^9\, \mathrm {M_{\odot }}$ 和 $2\times 10^{10}\, \mathrm{M_{\odot }}$)。我们发现，在大多数情况下，动态变热是一种诱导瞬态，例如，由于星系相互作用和合并活动，而不是作为恒星形成圆盘星系的年龄依赖性演化阶段。动态热但仍然活跃的恒星形成圆盘显示出一个共同的特征，即拥有运动学错位的气体和恒星圆盘，以及中心集中的持续恒星形成。前者通常伴随着扰乱的气体形态，而后者则反映在与动态冷的正常圆盘对应物相比的低气体和恒星自旋中。有趣的是，从 MaNGA 观测到的具有气体和恒星运动学失准的星系显示出与 IllustrisTNG 星系非常相似的一般特性，因此是真实世界的对应物。反过来，这使我们能够预测这些错位星系的恒星轨道和气体特性。