Cosmic-Ray Diffusion Suppression in Star-forming Regions Inhibits Clump Formation in Gas-rich Galaxies
Cosmic-Ray Diffusion Suppression in Star-forming Regions Inhibits Clump Formation in Gas-rich Galaxies
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DOI：
10.3847/1538-4357/abe2a6
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发表时间：
2020-12
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影响因子：
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通讯作者：
V. Semenov;A. Kravtsov;D. Caprioli
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文献类型：
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作者：
V. Semenov;A. Kravtsov;D. Caprioli
对星星团、孤立超新星遗迹和脉冲星风星云周围γ射线辐射的观测表明，加速点附近的宇宙射线（CR）扩散系数与银河系平均值相比可以被抑制一个很大的因子。我们探讨了这种局部抑制CR扩散对星系演化的影响，使用孤立的盘状星系与定期和高气体分数的模拟。我们的研究结果表明，而CR传播与恒定的扩散率可以使气体磁盘更稳定，通过增加中面压力，大规模的CR压力梯度不能防止局部破碎时，磁盘是不稳定的。相比之下，当CR扩散率在恒星形成区域被抑制时，CR在这些区域的积累会导致强烈的局部压力梯度，从而阻止大规模气体团块的形成。结果，致密气体的分布和星星的形成发生了质的变化：一个全球不稳定的气体盘不会剧烈地碎裂成大质量的恒星形成团块，而是保持着规则的大设计螺旋结构。这种影响调节星星的形成和磁盘结构，是定性不同和互补的全球作用的CR垂直流体静力学支持的气体磁盘和驱动银河风。
Observations of the γ-ray emission around star clusters, isolated supernova remnants, and pulsar wind nebulae indicate that the cosmic-ray (CR) diffusion coefficient near acceleration sites can be suppressed by a large factor compared to the Galaxy average. We explore the effects of such local suppression of CR diffusion on galaxy evolution using simulations of isolated disk galaxies with regular and high gas fractions. Our results show that while CR propagation with constant diffusivity can make gaseous disks more stable by increasing the midplane pressure, large-scale CR pressure gradients cannot prevent local fragmentation when the disk is unstable. In contrast, when CR diffusivity is suppressed in star-forming regions, the accumulation of CRs in these regions results in strong local pressure gradients that prevent the formation of massive gaseous clumps. As a result, the distribution of dense gas and star formation changes qualitatively: a globally unstable gaseous disk does not violently fragment into massive star-forming clumps but maintains a regular grand-design spiral structure. This effect regulates star formation and disk structure and is qualitatively different from and complementary to the global role of CRs in vertical hydrostatic support of the gaseous disk and in driving galactic winds.