标题： 利用ESPRESSO探测星系间介质的小尺度结构：延展QSO UM673的光谱学研究 显示英文标题

标题： Probing the small scale structure of the Inter-Galactic Medium with ESPRESSO: spectroscopy of the lensed QSO UM673

摘要： 红移 z = 2.719 的引力透镜化类星体 J014516.6-094517 已使用欧洲南方天文台甚大望远镜 (ESO VLT) 上的 ESPRESSO 仪器观测，以获得两个图像 A 和 B 的高保真光谱，分辨率为 R = 70000。 在所研究的红移范围内（2.1 < z < 2.7），两条视线上的 Lyman 森林相隔亚千秒差距的物理距离，并表现出强烈的关联性。 我们发现，这两个森林在当前信噪比水平下无法区分，并且没有显示出任何全局速度偏移，交叉相关峰值出现在$\Delta v = 12 \pm 48$m/s 处。 单个 Lyman-$\alpha$特征的速度差异分布与零平均值和 930 m/s 的平均绝对偏差一致。 未检测到 NHI 柱密度的显著差异，在$\leq 1$适当的 kpc 尺度上限制了重子密度的均方根波动至$\Delta \rho / \rho < 3$%。 另一方面，金属线在速度结构和柱密度方面显示出显著差异。 一个玩具模型表明，两条视线之间金属特征的速度差异与典型质量为$M\simeq 2\times 10^{10} M_\odot$的暗物质晕相关的重子组分运动一致，也与金属系统的观测出现率一致。 目前的观测证实了使用遥远明亮类星体的 Lyman 森林的高保真光谱进行宇宙红移漂移 Sandage 测试的可行性，但也对使用金属特征时伴随的固有噪声提供了警示。 显示英文摘要

摘要： The gravitationally lensed quasar J014516.6-094517 at z=2.719 has been observed with the ESPRESSO instrument at the ESO VLT to obtain high-fidelity spectra of the two images A and B with a resolving power R=70000. At the redshifts under investigation (2.1 < z < 2.7), the Lyman forests along the two sightlines are separated by sub-kiloparsec physical distances and exhibit a strong correlation. We find that the two forests are indistinguishable at the present level of signal-to-noise ratio and do not show any global velocity shift, with the cross-correlation peaking at $\Delta v = 12 \pm 48$ m/s. The distribution of the difference in velocity of individual Lyman-$\alpha$ features is compatible with a null average and a mean absolute deviation of 930 m/s. Significant differences in NHI column density are not detected, putting a limit to the RMS fluctuation in the baryon density on $\leq 1$ proper kpc scales of $\Delta \rho / \rho < 3$%. On the other hand, metal lines show significant differences both in velocity structure and in column density. A toy model shows that the difference in velocity of the metal features between the two sightlines is compatible with the the motions of the baryonic component associated to dark matter halos of typical mass $M\simeq 2\times 10^{10} M_\odot$, also compatible with the observed incidence of the metal systems. The present observations confirm the feasibility of the Sandage test of the cosmic redshift drift with high-fidelity spectroscopy of the Lyman forest of distant, bright quasars, but also provide an element of caution about the intrinsic noise associated to the usage of metal features for the same purpose.