AI 中文总结
本研究利用ASKAP-FLASH巡天在0.4<z<1.0范围内搜索HI 21厘米吸收线，新检测到一条射电星系的HI吸收线，首次实现伴生星系的叠加 tentative 检测，明确了影响叠加检测的关键因素。
AI 中文摘要
我们利用ASKAP的FLASH HI 21厘米吸收线巡天，对红移0.4 < z < 1.0范围内的恒星形成星系和射电星系对照样本中的伴生及 intervening HI 21厘米吸收线进行搜索并公布结果。我们报告在射电星系NVSS J214954-004657中检测到一条新的HI 21厘米吸收线，其HI红移z_HI = 0.863。此外，我们公布了伴生及 intervening 恒星形成星系和射电星系目录的HI 21厘米叠加分析结果。在该红移范围内，我们首次报告了按射电源亮度降序叠加时，伴生星系的HI 21厘米吸收线叠加检测结果，且显示当叠加越来越弱的源时，光学深度增加会导致这些 tentative 检测结果被掩盖。在叠加 intervening 星系的光谱时，未检测到叠加信号。我们推测，检测到叠加HI 21厘米信号的能力取决于背景源的光学深度极限以及源覆盖因子；覆盖因子在叠加 intervening 系统时影响更大，可被视为有效削弱射电源的观测流量密度。我们发现，在相同红移下，恒星形成星系中伴生HI 21厘米吸收线的检测率与一般射电源群体无显著差异。尽管检测率较低，但通过对HI 21厘米巡天的元分析，我们发现根据巡天参数预计会有1次检测结果。
英文摘要
We present results of a search for associated and intervening HI 21 cm absorption in star-forming galaxies and a control sample of radio galaxies at 0.4 < $z$ < 1.0, using ASKAP's FLASH HI 21 cm absorption survey. We report the detection of a new HI 21 cm absorption line in radio galaxy NVSS J214954-004657 at $z_{\mathrm{HI}}$ = 0.863. Additionally, we present results of HI 21 cm stacking for associated and intervening star-forming and radio galaxy catalogues. For the first time at these redshifts, we report tentative detections of stacked HI 21 cm absorption for associated galaxies when stacked in order of descending radio source brightness, and show that these tentative detections become buried as optical depth increases as progressively weaker sources are co-added into the stack. No stacked signal is detected when co-adding intervening galaxy spectra. We speculate that the ability to detect a stacked HI 21 cm detection is dependent on the background source optical depth limits, as well as source covering factors. Covering factor has a greater impact when stacking intervening systems, and can be considered to effectively weaken the observed flux density of a radio source. We find no significant difference in detection rate for associated HI 21 cm absorption in star-forming galaxies versus the general radio-source population at the same redshift. Although detection rates are low, from a meta-analysis of HI 21 cm surveys we find that 1 detection is expected given the survey parameters.
Comments20 pages, 12 figures, accepted for publication in MNRAS
