盘星系中纤维与羽毛结构的形成：自引力足够吗？
Formation of filaments and feathers in disc galaxies: Is self-gravity enough?
AI总结：
本研究通过三维自引力等温盘星系模拟，表明仅靠自引力与旋转即可形成与观测相符的 kpc 尺度纤维/羽毛，其形成受 Toomre Q 控制、形态由旋转马赫数决定。
摘要：
背景。致密纤维/羽毛是存在于近邻主序星系中的 kpc 尺度尘埃特征。与旋臂不同，纤维构成了致密气体聚集的主要部分。它们预计在恒星形成中发挥重要作用，并且已知其中存在恒星形成区和 H II 区。目标。我们通过全局引力不稳定性探讨盘星系中纤维/羽毛的起源。方法。我们采用孤立盘星系的三维流体动力学模拟开展参数研究，这些星系为等温、自引力体系，并以平衡状态初始化。我们的星系由两个无量纲参数唯一表征，即 Toomre $Q$ 和旋转马赫数 $\mathcal{M}_{\rm c}=v_{\rm c}/c_{\rm s}$（圆周速度与声速之比）。我们进行了覆盖二者广泛范围的模拟。结果。我们发现，$Q=1$ 的星系在一次自转之内形成纤维，而 $Q\geq2$ 的星系则不会。这些纤维长达 kpc，并沿方位角呈半规则间隔分布。其形态、密度对比和形成时间尺度随 $\mathcal{M}_{\rm c}$ 变化：纤维间距和不稳定性起始时间均与 $\mathcal{M}_{\rm c}$ 成反比，而密度对比随 $\mathcal{M}_{\rm c}$ 增大。然而，在所有 $Q=1$ 的星系中，其增长率均约为 $0.5~Ω$，其中 $Ω$ 为角频率。我们将模拟中的纤维间距与 JWST/MIRI 及 HST 对近邻星系的观测结果进行比较，发现二者一致。结论。我们的研究表明，即使不存在旋臂或磁场，自引力和旋转也足以形成纤维。其形态主要由 $\mathcal{M}_{\rm c}$ 决定，该参数刻画了热支撑相对于旋转支撑的重要性。
英文摘要：
Context. Dense filaments/feathers are kpc-scale dusty features present in nearby main sequence galaxies. Distinct from the spiral arms, filaments constitute a major portion of dense gas concentration. They are expected to play an important role in star formation and are known to harbour star-forming regions and H II regions. Aims. We explore the origin of filaments/feathers in disc galaxies via global gravitational instability. Methods. We conduct a parameter study using three-dimensional hydrodynamical simulations of isolated disc galaxies that are isothermal, self-gravitating and initialised in equilibrium. Our galaxies are uniquely characterised by two dimensionless parameters, the Toomre $Q$ and the rotational Mach number, $\mathcal{M}_{\rm c} = v_{\rm c}/c_{\rm s}$ (ratio of circular velocity to sound speed). We carry out simulations covering a wide range in both. Results. We find that galaxies with $Q = 1$ form filaments within a single rotation, while galaxies with $Q \geq 2$ do not. These filaments are kpc long and are semi-regularly spaced along the azimuth. Their morphology, density contrast and formation timescale vary with $\mathcal{M}_{\rm c}$, with filament spacing and instability onset time both inversely proportional to $\mathcal{M}_{\rm c}$ and the density contrast increasing with $\mathcal{M}_{\rm c}$. However, their growth rates in all $Q = 1$ galaxies are $\sim 0.5~Ω$, where $Ω$ is the angular frequency. We compare the filament spacing in our simulations with the ones from JWST/MIRI and HST observations of nearby galaxies and find them in agreement. Conclusions. Our study suggests that self-gravity and rotation are sufficient to form filaments, even in the absence of spiral arms or magnetic fields. Their morphologies are primarily determined by $\mathcal{M}_{\rm c}$, which parametrises the importance of thermal versus rotational support.
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