Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages
Abstract
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 {Hz0, qz0, jz0} 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) ≈ −Δz/[Δt (1+z)]; the one from the reddest envelope of CCs gives H(z ≈ 0.61) = 88.5+6.7−12.6 (stat.) ± 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.
Related
- Toward Bayesian photometric cosmic chronometers: Application to VIPERS
- How Steep is your Dust? Direct Measurements of Nebular Attenuation Curves at Cosmic Noon with JWST
- Joint Model-independent Constraints on the Post-Newtonian Parameter and Cosmic Curvature from Galaxy-scale Strong Lensing, SNe Ia, BAO, and Cosmic Chronometers
- Identification of Cosmic Chronometers in the GAMA Survey
- Is the Kaniadakis deformation of holographic dark energy detectable? A non-flat analysis with DESI DR2, cosmic chronometers and Pantheon+SH0ES
BibTeX
@misc{alvarez2026cosmography,
title = {{Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages}},
author = {Carlos A. Álvarez and Marcos M. Cueli and Balakrishna S. Haridasu and Michele Moresco and Martina Torsello and Alessandro Bressan and Lumen Boco and Luigi Danese and Andrea Lapi},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2608.13178},
eprint = {2608.13178},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.13178},
}
RIS
TY - UNPB
TI - Cosmography with DESI-DR1 Cosmic Chronometers: Direct H(z) measurements from Luminous Red Galaxy ages
AU - Carlos A. Álvarez
AU - Marcos M. Cueli
AU - Balakrishna S. Haridasu
AU - Michele Moresco
AU - Martina Torsello
AU - Alessandro Bressan
AU - Lumen Boco
AU - Luigi Danese
AU - Andrea Lapi
PY - 2026
DA - 2026/10/30
PB - arXiv
DO - 10.48550/arxiv.2608.13178
UR - https://arxiv.org/abs/2608.13178
AB - 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) ≈ −Δz/[Δt (1+z)]; the one from the reddest envelope of CCs gives H(z ≈ 0.61) = 88.5^+6.7_−12.6 (stat.) ± 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.
ER -