快速射电暴（FRB）是具有大色散测量的毫秒持续时间瞬态。FRB的起源仍然是个谜。了解FRB起源的方法之一是探测FRB宿主星系的物理环境。绘制FRB宿主星系中的分子气体运动学是至关重要的，因为它导致恒星形成，这可能与FRB祖先的诞生有关。然而，大多数以前的工作都集中在它的恒星组成的FRB宿主星系。因此，我们首次在$z= 0.3216$上报道了非重复FRB 180924 B宿主星系中的分子气体运动学。利用阿塔卡玛大型毫米/亚毫米波阵（ALMA）在其宿主星系中探测到CO（3-2）发射线的两个速度分量：一个分量的峰值（$-155.40$ km s $^{-1}$）位于宿主星系中心附近，另一个分量的峰值（$-7.76$ km s $^{-1}$）位于FRB位置附近. CO（3-2）谱显示出具有A $_{\rm peak}$ $=2.03\pm 0.39$的不对称轮廓，其中A $_{\rm peak}$是两个速度分量之间的峰值通量密度比。CO（3-2）速度图也显示出从$-180$ km s $^{-1}$到8 km s $^{-1}$的非对称速度梯度。这些结果表明宿主星系中分子气体的动力学结构受到了干扰。这种扰动的动力学结构的重复FRB宿主星系使用HI发射线在以前的工作中报告。我们的研究结果表明，非重复和重复FRB通常会出现在扰动动力学环境中，这表明气体运动学和FRB祖细胞之间可能存在联系。
英文摘要：
Fast radio bursts (FRBs) are millisecond-duration transients with large dispersion measures. The origin of FRBs is still mysterious. One of the methods to comprehend FRB origin is to probe the physical environments of FRB host galaxies. Mapping molecular-gas kinematics in FRB host galaxies is critical because it results in star formation that is likely connected to the birth of FRB progenitors. However, most previous works of FRB host galaxies have focused on its stellar component. Therefore, we, for the first time, report the molecular gas kinematics in the host galaxy of the non-repeating FRB 180924B at $z= 0.3216$. Two velocity components of the CO (3-2) emission line are detected in its host galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA): the peak of one component ($-155.40$ km s$^{-1}$) is near the centre of the host galaxy, and another ($-7.76$ km s$^{-1}$) is near the FRB position. The CO (3-2) spectrum shows asymmetric profiles with A$_{\rm peak}$ $=2.03\pm 0.39$, where A$_{\rm peak}$ is the peak flux density ratio between the two velocity components. The CO (3-2) velocity map also indicates an asymmetric velocity gradient from $-180$ km s$^{-1}$ to 8 km s$^{-1}$. These results indicate a disturbed kinetic structure of molecular gas in the host galaxy. Such disturbed kinetic structures are reported for repeating FRB host galaxies using HI emission lines in previous works. Our finding indicates that non-repeating and repeating FRBs could commonly appear in disturbed kinetic environments, suggesting a possible link between the gas kinematics and FRB progenitors.
Dispersion measures of fast radio burst host galaxies derived from IllustrisTNG simulation
本文计算了快射电爆发（FRB）主星系的色散测度（DM）。基于对几个宿主星系的观测，从IllustrisTNG模拟中选择了一个与观测星系具有相似性质的大样本星系。它们被用来计算主星系DM的分布，重复和非重复的FRB。对于重复的FRB，我们推断DM $ _{\mathrm{host}} $ FRB 121102和FRB 180916通过假设的爆发网站跟踪恒星形成率在宿主星系。对于FRB 121102和FRB 180916，中位DM $_{\mathrm{host}}$分别为$35 (1+z)^{1.08}$和$96(1+z)^{0.83}$ pc cm $^{-3}$。在另一种情况下，对于红移范围$z=0.1-1.5$的非重复FRB，DM $_{\mathrm{host}}$的中值约为$30 - 70$ pc cm $^{-3}$，假设爆发点是双星合并的位置。在这种情况下，可以通过$33(1+z)^{0.84}$ pc cm $^{-3}$计算中值DM $_{\mathrm{host}}$的演变。重复和非重复FRB的DM $_{\mathrm{host}}$的分布可以很好地拟合对数正态函数。我们的结果可用于推断非定域FRB的红移。
