使用ASKAP-FLASH搜寻遥远星系中的HI吸收 —— I. 射电样本的选择与分析
A search for HI absorption in distant star-forming galaxies with ASKAP-FLASH -- I. Selection and analysis of the radio sample
AI总结：
本研究构建了两个UV-selected星系目录，用于未来搜寻红移0.4<z<1的21 cm HI吸收，通过分析光学光谱发现impact parameter<5角秒的星系更可能与射电源物理关联且AGN概率高，而5-20角秒的多为star-forming，为后续HI吸收研究奠定基础。
摘要：
我们展示并讨论了两个UV-selected（NUV < 22.8 mag）星系目录，这些星系位于ASKAP FLASH巡天覆盖的200平方度天区内，且与FLASH射电连续谱源的impact parameter小于20角秒。这些目录旨在为未来搜寻红移0.4 < z < 1内星系内及周围的21 cm HI吸收提供支持。我们概述了这一UV-bright数据集的制作过程，该数据集包含来自WiggleZ和SDSS巡天的光学光谱，中值红移约为0.6。使用多个diagnostic diagrams对光学光谱分析表明，impact parameter小于5角秒的星系可能与射电源存在物理关联，且成为AGN的概率是未匹配射电源天体的五倍。相反，impact parameter在5到20角秒之间的天体大多（>80%）为star-forming，与整体WiggleZ样本相似。随红移的(g - i)颜色演化与active star-formation历史一致，但射电关联天体通常更红，颜色与high-excitation radio galaxies相近。尽管具有罕见的射电特性，两个目录的红移分布与WiggleZ星系整体分布一致。未来获取新射电数据时可扩充这些目录，后续论文将报告HI吸收结果。
英文摘要：
We present and discuss two catalogues of UV-selected (NUV $< 22.8$ mag) galaxies that lie within a 200 deg$^2$ area of sky covered by the ASKAP FLASH survey and have an impact parameter of less than 20 arcsec to a FLASH radio continuum source. These catalogues are designed to enable a future search for 21 cm HI absorption in and around star-forming galaxies at redshift $0.4<z<1$. We outline the production of this UV-bright dataset, which has optical spectroscopy from the WiggleZ and SDSS surveys and a median redshift of $\sim0.6$. Analysis of the optical spectra, using multiple diagnostic diagrams, shows that galaxies with an impact parameter of less than 5 arcsec are likely to be physically associated with the radio source and are five times more likely to be an AGN than objects without a radio match. Conversely, objects with impact factors between 5 and 20 arcsec are largely (>80 percent) star-forming and resemble the overall WiggleZ population. The ($g - i$) colour evolution with redshift is consistent with a history of active star-formation, but the radio-associated objects are typically redder and have colours similar to high-excitation radio galaxies. The redshift distribution of the two catalogues matches the overall distribution for WiggleZ galaxies, despite their otherwise rare radio properties. These catalogues can be expanded in future as new radio data become available, and a forthcoming paper will present the HI absorption results.
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