标题： 利用星暴星系背景照明器在前景延展盘中发现了一个低红移的Ly$α$ 系统 显示英文标题

标题： Discovery of a Low-Redshift Damped Ly$α$ System in a Foreground Extended Disk Using a Starburst Galaxy Background Illuminator

摘要： 我们报告了在背景星暴星系 SDSS J111323.88+293039.3 ($z=0.17514$) 光谱中发现的一个低红移饱和 Ly$\alpha$(DLA) 系统。该 DLA 系统距离形成恒星的星系 SDSS J111324.08+293051.2 ($z=0.17077$) 的冲击参数为$\rm \rho=36~kpc$。我们测量了 HI 柱密度为$N($HI$)\rm =3.47\times10^{20}~cm^{-2}$，并且还检测到多种低电离态元素，例如 NI、NII、SiII、CII 和 SiIII。我们还估计了覆盖分数为 0.883，从而得出 DLA 的极限大小为$A_{DLA}\rm \geq3.3~kpc^2$。 假设整个DLA系统具有均匀的柱密度，我们估计其质量为$M_{DLA}\geq5.3\times 10^6~M_\odot$。 这个DLA系统的扩展光源和较低的红移为我们提供了独特的机会来表征其性质及其与宿主星系的联系。 我们测量出该DLA相对于宿主星系系统速度的偏移量为+131 km s$^{-1}$。 这一速度距离使用新构建的旋转曲线测得的宿主星系投影旋转速度相差$-84$ km s$^{-1}$。 基于宿主星系的大小、氢柱密度以及气体动力学特性，我们认为此DLA正在追踪前景星系HI盘中的温中性气体。 我们的探测结果增加了少量已确认宿主星系的低红移DLA集合，并且是首次通过扩展背景源发现的。 显示英文摘要

摘要： We present the discovery of a low-redshift damped Ly$\alpha$ (DLA) system in the spectrum of background starburst galaxy SDSS J111323.88+293039.3 ($z=0.17514$). The DLA is at an impact parameter of $\rm \rho=36~kpc$ from the star forming galaxy, SDSS J111324.08+293051.2 ($z=0.17077$). We measure an HI column density of $N($HI$)\rm =3.47\times10^{20}~cm^{-2}$ along with multiple low-ionization species such as NI, NII, SiII, CII, and SiIII. We also make an estimate of the covering fraction to be 0.883, giving us a limiting size of the DLA to be $A_{DLA}\rm \geq3.3~kpc^2$. Assuming a uniform column density over the entire DLA system, we estimate its mass to be $M_{DLA}\geq5.3\times 10^6~M_\odot$. The extended illuminator and the low redshift of this DLA give us the unique opportunity to characterize its nature and the connection to its host galaxy. We measure a velocity offset of +131 km s$^{-1}$ from the systemic velocity of the host for the DLA. This velocity is $-84$ km s$^{-1}$ from the projected rotation velocity of the host galaxy as measured using a newly constructed rotation curve. Based on the size of the host galaxy, the HI column density, and the gas kinematics, we believe this DLA is tracing the warm neutral gas in the HI disk of the foreground galaxy. Our detection adds to a small set of low-redshift DLAs that have confirmed host galaxies, and is the first to be found using an extended background source.