[论文解读] The effect of radiation pressure on dust distribution inside HII regions

Shohei Ishiki, Takashi Okamoto+1 more|arXiv (Cornell University)|Aug 23, 2017

Astrophysics and Star Formation Studies被引用 1

一句话总结

本研究利用包含尘埃吸收、再辐射及粒径分辨的1D辐射流体动力学模拟，表明辐射压在致密HII区中引发了一个约0.2 pc的尘埃空洞。库仑阻力比碰撞阻力强两个数量级，且辐射压改变了尘埃粒径分布，使大颗粒与小颗粒的质量比降低一个数量级，更强的辐射源因增强尘埃带电而削弱了粒径分离效应。

ABSTRACT

We investigate the impact of radiation pressure on spatial dust distribution inside H$_\mathrm{II}$ regions using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. In order to investigate grain size effects as well, we introduce two additional fluid components describing large and small dust grains in the simulations. Relative velocity between dust and gas strongly depends on the drag force. We include collisional drag force and coulomb drag force. We find that, in a compact H$_\mathrm{II}$ region, a dust cavity region is formed by radiation pressure. Resulting dust cavity sizes (~0.2 pc) agree with observational estimates reasonably well. Since dust inside an H$_\mathrm{II}$ region is strongly charged, relative velocity between dust and gas is mainly determined by the coulomb drag force. Strength of the coulomb drag force is about 2-order of magnitude larger than that of the collisional drag force. In addition, in a cloud of mass $10^5$ $M_{\odot}$, we find that the radiation pressure changes the grain size distribution inside H$_\mathrm{II}$ regions. Since large (0.1 $\mathrm{\mu m}$) dust grains are accelerated more efficiently than small (0.01 $\mathrm{\mu m}$) grains, the large to small grain mass ratio becomes smaller by an order of magnitude compared with the initial one. Resulting dust size distributions depend on the luminosity of the radiation source. The large and small grain segregation becomes weaker when we assume stronger radiation source, since dust grain charges become larger under stronger radiation and hence coulomb drag force becomes stronger.

研究动机与目标

• 研究辐射压如何影响HII区中尘埃的分布。
• 考察在辐射压作用下，尘埃粒径差异在尘埃动力学中的作用。
• 评估碰撞阻力与库仑阻力在尘埃-气体解耦中相对重要性。
• 确定辐射源光度如何影响尘埃粒径分离。

提出的方法

• 包含光子吸收与再辐射的1维辐射流体动力学模拟。
• 额外引入两个流体组分，分别代表大（0.1 µm）和小（0.01 µm）尘埃颗粒。
• 阻力力包括碰撞阻力与库仑阻力，后者因尘埃强烈带电而占主导。
• 模拟以10⁵ M☉的云气为对象，评估尘埃空洞形成与尘埃分布变化。
• 改变辐射源光度以研究其对尘埃分离与阻力力的影响。
• 追踪尘埃粒径分布演化，量化大颗粒与小颗粒质量比的变化。

实验结果

研究问题

• RQ1 辐射压如何影响致密HII区中尘埃的空间分布？
• RQ2 碰撞阻力与库仑阻力在尘埃-气体解耦中的相对贡献如何？
• RQ3 辐射压在多大程度上改变了HII区内部的尘埃粒径分布？
• RQ4 中心离化源的光度如何影响尘埃分离与尘埃空洞形成？

主要发现

• 由于辐射压作用，致密HII区中形成了约0.2 pc的尘埃空洞，与观测估计一致。
• 库仑阻力比碰撞阻力强约两个数量级，主导尘埃-气体相对速度。
• 在10⁵ M☉云气中，由于辐射压效应，大颗粒与小颗粒的质量比降低了整整一个数量级。
• 更强的辐射源会削弱尘埃粒径分离，因为更高的电离度增加了尘埃电荷，从而增强了库仑阻力。
• 在辐射压作用下，尘埃粒径分布发生显著演化，大颗粒被更高效地加速。
• 最终的尘埃粒径分布取决于中心辐射源的光度，光度越高，粒径分离效应越弱。