AI 中文总结
本研究构建半解析模型并开展辐射流体模拟，发现年轻贫尘埃H II区可产生高DM，解释FRB的低金属丰度宿主偏好，或助力获得更纯净的FRB样本以研究星系际介质。
AI 中文摘要
若干重复快速射电暴（FRB）源展现出宿主帧色散量（DM）超出值，远超其宿主星系星际介质预期值，这意味着亚千秒差距尺度的局域环境有显著贡献。这些超出值常被归因于膨胀的超新星遗迹，但该经典解释无法说明其对低金属丰度矮星系宿主的明显偏好，表明产生局域DM的机制与宿主星系特性相关。本研究探究由年轻大质量星协产生的H II区是否能同时解释这些DM超出值及其与低金属丰度矮星系的偏好关联。我们构建了团形成分子云中FRB辐射中子星的半解析模型，并使用pySTARBURST99的时变电离光度开展理想化一维辐射流体动力学模拟。研究结果表明，低金属丰度环境（类似大麦哲伦云或更低）中，大质量（恒星质量M★~10^5-10^6 M☉）、年轻（≤10 Myr）的星协，可对早期（≤5 Myr）形成且仍嵌于电离气体中的FRB产生DM_H II≥10^3 pc·cm^-3。对低质量/金属丰度的偏好源于尘埃：莱曼连续谱的吸收会抑制高金属丰度下的电离柱密度，使极端局域DM优先在贫尘埃、低金属丰度环境中产生。在宇宙学距离上，选择金属丰度高、质量大且宁静的宿主星系样本（其中此类极端局域贡献可能被抑制），可得到更纯净的FRB样本，用于将河外DM作为星系际介质和周星系介质的示踪物。
英文摘要
Several repeating fast radio burst (FRB) sources exhibit host-frame dispersion measure (DM) excesses far exceeding those expected from the interstellar medium in their host galaxies, implying a substantial contribution from the sub-kiloparsec-scale local environment. These excesses are often attributed to an expanding supernova remnant; however, this canonical interpretation does not explain their apparent preference for low-metallicity dwarf galaxy hosts, suggesting that the mechanism producing the local DM is coupled to the properties of the host galaxy. In this work, we investigate whether the H II regions generated by young, massive stellar associations can simultaneously explain these DM excesses and their preferential association with low-metallicity dwarf galaxies. We develop a semi-analytic model for FRB-emitting neutron stars in cluster-forming molecular clouds and perform idealized one-dimensional radiation-hydrodynamic simulations using time-dependent ionizing luminosities from pySTARBURST99. Our findings indicate that high-mass $(M_\star \sim 10^5-10^6\;M_\odot)$, young ($\lesssim 10\;{\rm Myr}$) stellar associations in low-metallicity environments (LMC-like or lower) can produce ${\rm DM}_{\rm HII} \gtrsim 10^3\;{\rm pc\;cm^{-3}}$ for FRBs that form early ($\lesssim 5$ Myr) and remain embedded in the ionized gas. The low-mass/metallicity preference arises from dust: absorption of the Lyman continuum suppresses the ionized column at higher metallicity, making extreme local DMs preferentially generated in dust-poor, low-metallicity environments. At cosmological distances, selection of a metal-rich, massive, and quiescent host galaxy sample where such extreme local contributions are likely to be suppressed may yield a cleaner FRB sample for using extragalactic DMs as tracers of the intervening intergalactic and circumgalactic media.
Comments32 pages, 9 figures, 1 table
