利用CHIME/FRB目录2约束M31离子化物质晕的质量
Constraining the mass of the M31 ionized baryon Halo using CHIME/FRB Catalog 2
AI总结：
利用CHIME/FRB目录2中的FRB数据，研究M31晕的中性物质分布，发现其CGM质量为18.6±7.9×10¹⁰M_⊙，表明M31可能拥有大量稀疏离子化气体。
摘要：
银河系周围的星系际介质（CGM）被认为是重要的中性物质库，但其总质量仍缺乏精确约束。我们提出了一种利用CHIME/FRB目录2中的快速射电暴（FRB）来探测M31星系（仙女座星系）CGM的新方法。通过比较171个视线穿过M31晕（在r_vir=302kpc内）的FRB的散射测量（DMs）与684个对照样本FRB的DM，我们估计了M31 CGM的DM贡献。我们发现内晕（约0-151kpc）存在DM超额δDM=5.9-59.6pc cm⁻³，外晕（约151-302kpc）δDM=25.7-64.6pc cm⁻³。利用一个由闭合半径r_close参数化的通用晕模型，我们约束了物质分布并推断出最佳拟合的r_close值为9.2⁺9.9⁻4.9r_vir（1σ），对应总CGM质量为M_b,halo=18.6⁺7.9⁻8.4×10¹⁰M_⊙。我们的结果表明，M31可能在稀疏、离子化气体中拥有相当大的宇宙中性物质预算。这项工作展示了FRB在研究邻近星系CGM中的潜力，未来更大的样本预计能提供更精确的星系晕中性物质含量约束。
英文摘要：
The circumgalactic medium (CGM) surrounding galaxies is believed to be a significant reservoir of baryons, yet its total mass remains poorly constrained. We present a novel approach to probe the CGM of the Andromeda galaxy (M31) using fast radio bursts (FRBs) from the CHIME/FRB Catalog 2. By comparing the dispersion measures (DMs) of 171 FRBs whose sightlines intersect M31's halo (within $r_{\rm vir}= 302\,\mathrm{kpc}$) to a control sample of 684 FRBs, we estimate the DM contribution from M31's CGM. We find evidence for an excess DM of $δ\mathrm{DM} = 5.9$--$59.6\,\mathrm{pc\,cm^{-3}}$ in the inner halo ($\approx 0$--$151\,\mathrm{kpc}$) and $δ\mathrm{DM} = 25.7$--$64.6\,\mathrm{pc\,cm^{-3}}$ in the outer halo ($\approx 151$--$302\,\mathrm{kpc}$). Using a generalized halo model parameterized by a closure radius $r_{\mathrm{close}}$, we constrain the baryon distribution and infer a best-fit value for $r_{\mathrm{close}}$ to be $9.2^{+9.9}_{-4.9}\,r_{\rm vir}$ ($1σ$), corresponding to a total CGM mass of $M_{b,\mathrm{halo}} = 18.6^{+7.9}_{-8.4} \times 10^{10}\,M_\odot$. Our results suggest that M31 may harbor a substantial fraction of its cosmic baryon budget in diffuse, ionized gas. This work demonstrates the potential of FRBs as a powerful tool for studying the CGM of nearby galaxies, with future larger samples expected to provide tighter constraints on the baryon content of galactic halos.
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