快速射电暴21厘米吸收线盲测。III. 21厘米吸收体样本中的OH吸收线搜索及持续的HI吸收线搜索
The FAST HI 21-cm Absorption Blind Survey. III. OH Absorption Search in the 21-cm Absorber Sample and Continued HI Absorption Search
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中文总结 AI 辅助
利用FAST对HI 21厘米吸收线进行盲测并扩展搜索，同时首次对OH 18厘米吸收线盲测，重新检测到已知OH吸收体，未发现新的，研究两者关系无显著证据，还给出OH柱密度上限，为相关研究设基准并铺平未来大规模调查道路。
中文摘要 AI 辅助
我们介绍了利用五百米口径球面射电望远镜（FAST）首次对OH 18厘米吸收线进行的盲测，该测试与HI 21厘米吸收线搜索同时进行。我们之前的FAST盲测HI吸收线搜索识别出了34个系统。在这项工作中，我们利用2024年以及2025年部分CRAFTS和FASHI数据（394.4小时和1622.1平方度）以及FATHOMER观测结果进行扩展搜索，得到了3个已知和4个新的HI吸收体，共41个HI吸收线系统。我们在19个HI吸收线系统中搜索OH吸收线，其OH红移频率落在FAST频段内。重新检测到了朝向PKS 1413+135的已知OH吸收体，使我们的调查成为首次检测到OH吸收线的盲测。未识别出新的OH吸收体。我们研究了$N_{\rm{OH}}$和$N_{\rm{HI}}$之间的关系，应用生存分析来考虑上限。分析未提供$N_{\rm{OH}}$-$N_{\rm{HI}}$相关性或$N_{\rm{OH}}$/$N_{\rm{HI}}$红移演化的统计显著证据。最后，光谱堆叠为相关、居间和组合样本设置了3$\sigma$的OH柱密度上限，分别为4.93、1.64和1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$，对应于[\rm{OH}]/[\rm{HI}]比值<$1.66\times$10$^{-8}$、<$1.42\times$10$^{-8}$和<$0.90\times$10$^{-8}$，假设OH的$T_{\rm{ex}}$ = 10K，HI的$T_{\rm{s}}$ = 100K。这些结果对射电选择的HI吸收体中的OH含量施加了迄今为止最强的限制，并为HI选择系统中分子气体的未来研究建立了盲测基准。它们还表明，已知的HI 21厘米吸收体为系统的OH吸收线搜索提供了有效的母样本，为未来更大规模的调查铺平了道路。
英文摘要
We present the first blind search for OH 18-cm absorption with the Five-hundred-meter Aperture Spherical Telescope (FAST), conducted alongside the HI 21-cm absorption search. Our previous FAST blind HI absorption search identified 34 systems. In this work, we extend the search using 2024 and part of the 2025 CRAFTS and FASHI data (394.4 hr and 1622.1 deg$^{2}$) together with FATHOMER observations, yielding three known and four new HI absorbers, for a total of 41 HI absorption systems. We search for OH absorption in 19 HI absorption systems whose OH redshifted frequencies fall within the FAST band. The known OH absorber towards PKS 1413+135 was re-detected, making our survey the first blind survey to detect OH absorption. No new OH absorbers were identified. We examine the relationship between $N_{\rm{OH}}$ and $N_{\rm{HI}}$, applying survival analysis to account for upper limits. The analysis does not provide statistically significant evidence for either an $N_{\rm{OH}}$-$N_{\rm{HI}}$ correlation or redshift evolution of $N_{\rm{OH}}$/$N_{\rm{HI}}$. Finally, spectral stacking sets 3$σ$ OH column density upper limits of 4.93, 1.64, and 1.72 $T_{\rm{ex}}$/$c_{\rm{f,OH}}\times$10$^{12}$cm$^{-2}$K$^{-1}$ for associated, intervening, and combined samples, corresponding to [\rm{OH}]/[\rm{HI}] ratios of $<$1.66$\times$10$^{-8}$, $<$1.42$\times$10$^{-8}$, and $<$0.90$\times$10$^{-8}$, assuming $T_{\rm{ex}}$=10K for OH and $T_{\rm{s}}$=100K for HI. These results place the strongest constraints to date on the OH content in radio-selected HI absorbers and establish a blind-survey benchmark for future studies of molecular gas in HI-selected systems. They also demonstrate that known HI 21-cm absorbers provide an effective parent sample for systematic OH absorption searches, paving the way for future larger surveys.
