宇宙偶然叠加：投影分离小于20 kpc的最大全面星系-类星体对目录
Cosmic Chance Superpositions: Largest Catalog of Quasar-Galaxy Pairs at a Projected Separation of $D \lesssim 20$ kpc
AI总结：
本研究通过分析1345个星系-类星体对，揭示了盘晕界面气体和尘埃的丰富特性，并首次检测到弥散星际带。
摘要：
我们目前呈现了迄今为止最大的银河系位于类星体之上（GOTOQs）目录，这些系统中，背景类星体的视线直接穿过或非常接近前景星系。使用约110万条来自SDSS DR16和DESI早期数据释放的类星体光谱，我们在红移范围0.0045至1.09之间识别出1345个独特的GOTOQs，比之前已知的数量增加了四倍多。该目录结合了无吸收和有吸收的搜索方法，使能够对投影分离D小于20 kpc的星系中的气体进行统计上稳健的表征。GOTOQ发射线比值表明，其宿主星系主要是正常的恒星形成盘，具有典型的尘埃消光量A_V约为0.5 mag。我们测量了MgII覆盖分数在D小于20 kpc处，发现其显著高，fc=98.2±1.3下限-4.5上限%，表明这些系统追踪盘晕界面的气体丰富、金属富集区域。类星体视线的中位色指数E(B-V)=0.087显著高于典型MgII吸收体，强调了GOTOQ视线的尘埃丰富性质。从高信噪比复合光谱中，我们报告了首次统计检测到的弥散星际带在λ4428（W_r=0.055±0.011埃），揭示了盘晕界面存在复杂的有机分子。该目录为未来多波段研究气体流动、冷气体和尘埃演化提供了强大的参考样本。
英文摘要：
We present the largest catalogue to date of Galaxies On Top Of Quasars (GOTOQs), systems where the sightline to a background quasar passes directly through or very close to a foreground galaxy. Using $\approx$1.1 million quasar spectra from SDSS DR16 and the DESI Early Data Release, we identify 1345 unique GOTOQs over the redshift range $0.0045 \leq z \leq 1.09$, more than quadrupling the number previously known. The catalogue combines both absorption agnostic and absorption selected searches, enabling a robust characterization of gas in galaxies at projected separations $D \lesssim 20$ kpc. The GOTOQ emission line ratios indicate that their host galaxies are predominantly normal, star forming disks with typical dust extinctions of $A_V \approx 0.5$ mag. We measure the MgII covering fraction at $D \lesssim 20$ kpc and find it to be remarkably high, $f_c = 98.2^{+1.3}_{-4.5}$ per cent, indicating that these systems trace gas rich, metal enriched regions at the disk-halo interface. The median colour excess towards the quasar line of sight, $E(B-V) = 0.087$, is significantly higher than that of typical MgII absorbers, underscoring the dust rich nature of GOTOQ sightlines. From a high signal to noise composite spectrum, we report the first statistical detection of the diffuse interstellar band at $λ4428$ ($W_r = 0.055 \pm 0.011$ angstrom) and at $λ5780$ ($W_r = 0.051\pm 0.012$ angstrom), revealing the presence of complex organic molecules at the disk halo interface. This catalogue provides a powerful reference sample for future multi wavelength studies of gas flows, cold gas, and dust evolution in the inner circumgalactic medium.
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