Toward Bayesian photometric cosmic chronometers: Application to VIPERS
Abstract
The cosmic chronometer (CC) method provides a direct measurement of the expansion history of the universe, H(z), from the differential ages of passively evolving galaxies. However, most CC analyses rely on high-quality spectroscopy to select passive galaxies, measure age-sensitive spectral features, and control stellar-population systematics. We build on existing works that use the D4000 spectral break as a proxy for measuring galaxy ages and apply it to a photometry-selected galaxy sample from VIPERS PDR2 in the range 0.5 ≤ z ≤ 0.8. Our goal is to extend the scope of the standard CC framework to photometric surveys. To achieve this, we first selected a massive and passive galaxy sample using rest-frame colors and mass. Second, we designed a Bayesian framework to infer full galaxy age posteriors in fine redshift bins, using a D4000-age-metallicity grid from stellar population synthesis models. We marginalized over metallicity, using a Gaussian metallicity prior to break the D4000-age-metallicity degeneracy. Subsequently, we derived age-difference posteriors between redshift bins by convolving their age posteriors. Finally, using the median and errors extracted from the differential age posteriors, we calculated the weighted average H(z) over our selected redshift range. We obtain H(z=0.65)=93.68±28.27 (stat.)±10.67 (syst.) km s−1 Mpc−1, which is consistent with existing spectroscopic CC measurements and with the Λ cold dark matter (ΛCDM) model prediction from Planck at the same redshift. This result provides a proof of concept for extending direct H(z) measurements from cosmic chronometers to photometric and spectro-photometric surveys, where larger samples can compensate for lower spectral resolution, provided that passive-galaxy selection, metallicity priors, and stellar-population systematics are carefully controlled.
Versions
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BibTeX
@misc{pradhan2026toward,
title = {{Toward Bayesian photometric cosmic chronometers: Application to VIPERS}},
author = {Swaraj Pradhan and Pablo Renard and Enrique Gaztanaga and Malgorzata Siudek and Thibaud Moutard},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.07298},
eprint = {2606.07298},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.07298},
}
RIS
TY - UNPB
TI - Toward Bayesian photometric cosmic chronometers: Application to VIPERS
AU - Swaraj Pradhan
AU - Pablo Renard
AU - Enrique Gaztanaga
AU - Malgorzata Siudek
AU - Thibaud Moutard
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2606.07298
UR - https://arxiv.org/abs/2606.07298
AB - The cosmic chronometer (CC) method provides a direct measurement of the expansion history of the universe, H(z), from the differential ages of passively evolving galaxies. However, most CC analyses rely on high-quality spectroscopy to select passive galaxies, measure age-sensitive spectral features, and control stellar-population systematics. We build on existing works that use the D4000 spectral break as a proxy for measuring galaxy ages and apply it to a photometry-selected galaxy sample from VIPERS PDR2 in the range 0.5 ≤ z ≤ 0.8. Our goal is to extend the scope of the standard CC framework to photometric surveys. To achieve this, we first selected a massive and passive galaxy sample using rest-frame colors and mass. Second, we designed a Bayesian framework to infer full galaxy age posteriors in fine redshift bins, using a D4000-age-metallicity grid from stellar population synthesis models. We marginalized over metallicity, using a Gaussian metallicity prior to break the D4000-age-metallicity degeneracy. Subsequently, we derived age-difference posteriors between redshift bins by convolving their age posteriors. Finally, using the median and errors extracted from the differential age posteriors, we calculated the weighted average H(z) over our selected redshift range. We obtain H(z=0.65)=93.68±28.27 (stat.)±10.67 (syst.) km s^−1 Mpc^−1, which is consistent with existing spectroscopic CC measurements and with the Λ cold dark matter (ΛCDM) model prediction from Planck at the same redshift. This result provides a proof of concept for extending direct H(z) measurements from cosmic chronometers to photometric and spectro-photometric surveys, where larger samples can compensate for lower spectral resolution, provided that passive-galaxy selection, metallicity priors, and stellar-population systematics are carefully controlled.
ER -