Prescriptions for Correcting Ultraviolet-based Redshifts for Luminous Quasars at High Redshift
Prescriptions for Correcting Ultraviolet-based Redshifts for Luminous Quasars at High Redshift
复制标题
DOI：
10.3847/1538-4357/ab77b6
复制
发表时间：
2020-02
期刊：
影响因子：
--
通讯作者：
C. Dix;O. Shemmer;M. Brotherton;R. Green;M. Mason;A. Myers
中科院分区：
文献类型：
--
作者：
C. Dix;O. Shemmer;M. Brotherton;R. Green;M. Mason;A. Myers
高红移类星体的红移通常由静止框架紫外（UV）发射线确定。然而，与从静止帧光学发射线确定的红移相比，这些谱线，更具体地说是突出的 C iv λ1549 发射线，通常发生蓝移，产生高度不确定的红移估计。我们展示了 2.15 < z < 3.70 处 18 个发光类星体的近红外光谱，这使我们能够获得这些源的可靠的系统红移。结合 44 个具有可比光度和红移的类星体档案样本的近红外光谱，我们提供了校正基于紫外线的红移的处方。与目前用于确定此类值的最佳方法相比，我们的方案将系统红移的速度偏移减少了~140 km s−1，并将基于紫外线的红移的不确定性降低了~25%。我们还发现，斯隆数字巡天管道为我们的来源确定的红移存在很大的不确定性，而且无法轻易缓解。考虑到具有近红外光谱的高红移类星体样本，我们讨论了我们的方案改善基于紫外线的红移校正的潜力。
High-redshift quasars typically have their redshift determined from rest-frame ultraviolet (UV) emission lines. However, these lines, and more specifically the prominent C iv λ1549 emission line, are typically blueshifted yielding highly uncertain redshift estimates compared to redshifts determined from rest-frame optical emission lines. We present near-infrared spectroscopy of 18 luminous quasars at 2.15 < z < 3.70 that allows us to obtain reliable systemic redshifts for these sources. Together with near-infrared spectroscopy of an archival sample of 44 quasars with comparable luminosities and redshifts, we provide prescriptions for correcting UV-based redshifts. Our prescriptions reduce velocity offsets with respect to the systemic redshifts by ∼140 km s−1 and reduce the uncertainty on the UV-based redshift by ∼25% with respect to the best method currently used for determining such values. We also find that the redshifts determined from the Sloan Digital Sky Survey Pipeline for our sources suffer from significant uncertainties, which cannot be easily mitigated. We discuss the potential of our prescriptions to improve UV-based redshift corrections given a much larger sample of high-redshift quasars with near-infrared spectra.