利用DESI-DR1宇宙计时仪进行宇宙学测量：通过亮红星系年龄直接测量H(z)
Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages
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中文总结 AI 辅助
本研究利用DESI-DR1的亮红星系数据，通过宇宙计时仪方法，采用两种独立方式推导0.3<z<1.2的H(z)约束，得到H(z≈0.61)的测量值及相关不确定性。
中文摘要 AI 辅助
暗能量光谱仪（DESI）为近300万个亮红星系（LRG）提供了可靠的红移估计，为采用独立方法检验宇宙膨胀率提供了独特机会。我们将宇宙计时仪（CC）方法应用于DESI LRG的微分年龄演化，推导0.3<z<1.2范围内哈勃参数H(z)的新独立约束。我们通过光谱筛选选择光谱以确保样本纯度，移除恒星形成天体的污染，随后通过叠加构建可靠的宇宙计时仪（CC）样本，以获得稳定、高信噪比（S/N）的光谱，这也作为t-z平面的民主分箱选择。通过测量叠加光谱上的利克（Lick）指数并将其与理论恒星种群模型拟合来估计年龄。我们从获得的t-z关系中通过两种独立方法推导H(z)约束：采用 pivot 红移宇宙学拟合，以及从原始CC方法直接估计。宇宙学拟合得到运动学参数{Hz0, qz0, jz0}的后验分布，与当前考虑的宇宙学模型兼容，提供H(z)的精度水平估计。我们提供最大后验（MAP）H(z)估计、H-z平面中中位数置信区间的数组及其协方差矩阵。我们还利用不同速度弥散组的t-z关系的红移分布，采用离散近似H(z)≈−Δz/[Δt(1+z)]获得两个独立的局部测量；来自最红CC包络的测量给出H(z≈0.61)=88.5+6.7−12.6（统计）±8.1（系统）km s−1 Mpc−1。宇宙学和离散H(z)测量的系统不确定性来自对数据处理中所有方法选择的综合分析。
英文摘要
Providing robust redshift estimates for almost 3 million luminous red galaxies (LRGs), the Dark Energy Spectroscopic Instrument (DESI) offers a unique opportunity to test the expansion rate of the Universe with independent approaches. We apply the cosmic chronometer method to derive new, independent constraints on the Hubble parameter at 0.3<z<1.2 from the differential age evolution of DESI LRGs. We select spectra applying spectroscopic cuts to ensure sample purity and remove contamination by star-forming objects, then build a robust sample of cosmic chronometers (CCs) by stacking to obtain stable, high signal-to-noise (S/N) spectra, which also serves as a democratic binning choice for the $t-z$ plane. Ages are estimated by measuring Lick indices on the stacked spectra and fitting them with a theoretical stellar population model. We obtain $t-z$ relations from which we derive $H(z)$ constraints via two independent approaches: a fit with a pivotal-redshift cosmography, and a direct estimate from the original CC method. The cosmographic fit yields posteriors for the kinematic parameters $\{H_{z_0}, q_{z_0}, j_{z_0}\}$ compatible with currently considered cosmologies, giving a precision-level estimate of $H(z)$. We provide the maximum-a-posteriori (MAP) $H(z)$ estimate, an array of the median confidence region in the $H-z$ plane, and its covariance matrix. We also leverage the redshift distributions of the $t-z$ relation for different velocity dispersion groups to obtain two independent local measurements using the discrete approximation $H(z) \approx -Δz/[Δt (1+z)]$; the one from the reddest envelope of CCs gives $H(z \approx 0.61) = 88.5^{+6.7}_{-12.6}$ (stat.) $\pm 8.1$ (syst.) km s$^{-1}$ Mpc$^{-1}$. Systematic uncertainties for both the cosmographic and discrete $H(z)$ measurements come from a comprehensive analysis of all methodological choices in the data treatment.
