标题： 切连科夫望远镜阵列观测的耀星光学光谱学- IV 显示英文标题

标题： Optical spectroscopy of blazars for the Cherenkov Telescope Array Observatory- IV

摘要： 耀变体，包括BL Lacs和FSRQs，是亮度最高的河外{\gamma }-ray源。它们占最近费米- LAT目录（4FGL-DR4）中列出的源的约56%。BL Lacs的光学和紫外光谱几乎无特征，使得精确确定其红移变得困难。因此，近一半的{\gamma }-ray BL Lacs缺乏可靠的红移测量。这构成了一个主要挑战，因为红移对于研究耀变体种群的宇宙演化以及{\gamma }-ray传播研究（如EBL的间接证据、对IGMF的约束以及对LIV和ALPs的搜索）至关重要。本文是系列论文的第四篇，专门致力于确定一批被确定为未来切连科夫望远镜阵列观测（CTAO）关键目标的耀变体的红移。我们进行了蒙特卡洛模拟，以选择由费米-LAT检测到的具有硬光谱且缺乏红移测量的{\gamma }-ray耀变体。这些耀变体预计在30小时或更少的曝光下可通过CTAO检测到。在本文中，我们报告了使用ESO/VLT、凯克II和SALT望远镜对29个耀变体进行详细光谱观测的结果。我们的分析涉及对每个耀变体光谱中的光谱线进行全面搜索，当识别出宿主星系的特征时，我们对其特性进行了建模。我们还将观测期间目标的亮度与其长期光变曲线进行了比较。在研究的样本中，29个源中有9个以高信噪比（S/N > 100）进行了观测，其余20个则以中等或低信噪比进行了观测。我们成功地确定了12个耀变体的可靠红移，范围从0.1636到1.1427，并识别出两个红移下限，分别为z > 1.0196和z > 1.4454。其余15个BL Lac天体表现出无特征的光谱。 显示英文摘要

摘要： Blazars, including BL Lacs and FSRQs, are the most luminous extragalactic {\gamma}-ray sources. They account for about 56% of the sources listed in the recent Fermi-LAT catalog (4FGL-DR4). The optical and UV spectra of BL Lacs are nearly featureless, making it difficult to precisely determine their redshifts. Consequently, nearly half of the {\gamma}-ray BL Lacs lack reliable redshift measurements. This poses a major challenge, since redshift is crucial for studying the cosmic evolution of the blazar population and {\gamma}-ray propagation studies such as indirect evidence of EBL, placing constraints on IGMF and searches for LIV and ALPs. This paper is the fourth in a series dedicated to determining the redshift of a sample of blazars identified as key targets for future observations with the Cherenkov Telescope Array Observatory (CTAO). We performed Monte Carlo simulations to select {\gamma}-ray blazars detected by Fermi-LAT with hard spectra, that lack redshift measurements. These blazars are expected to be detectable by CTAO within 30 hours or less of exposure assuming an average flux state. In this fourth paper, we report the results of detailed spectroscopic observations of 29 blazars using the ESO/VLT, Keck II, and SALT telescopes. Our analysis involved a thorough search for spectral lines in the spectra of each blazar, and when features of the host galaxy were identified, we modeled its properties. We also compared the magnitudes of the targets during the observations to their long-term light curves. In the sample studied, 9 of 29 sources were observed with a high signal-to-noise ratio (S/N > 100), while the remaining 20 were observed with a moderate or low S/N. We successfully determined firm redshifts for 12 blazars, ranging from 0.1636 to 1.1427, and identified two lower limit redshifts at z > 1.0196 and z > 1.4454. The remaining 15 BL Lac objects exhibited featureless spectra.