Two-rung ladder: H0 from Tip of the Red Giant Branch and geometric anchors alone
Abstract
We infer the Hubble constant H0 from the ~400 Extragalactic Distance Database hosts with a tip of the red giant branch (TRGB) distance, calibrated on the geometric anchors of the Large Magellanic Cloud and NGC 4258. We forward-model the tip magnitudes and host redshifts including magnitude-limited selection, sky exposure, and density-dependent galaxy bias, conditioning on each of the 80 Manticore-Local realisations of the local density and peculiar-velocity fields in turn. As most hosts lie at czCMB ≲ 1000 km/s, where peculiar velocities are important, the inference is limited by the variance of these fields rather than by the TRGB calibration. For a fixed realisation, the redshift likelihood and density smoothing each move H0 by less than 1 km/s/Mpc and a velocity monopole by 5.4 ± 3.4 km/s/Mpc, whereas the field-to-field scatter in H0 is 5.2 km/s/Mpc. Weighting the posteriors from each realisation equally gives H0 = 68.4 ± 5.9 km/s/Mpc, while weighting each by its Bayesian evidence gives 72.3 ± 2.6 km/s/Mpc. The latter value is set by a single particularly high-evidence realisation, making it sensitive to the finite sampling of the reconstruction posterior. This ladder therefore cannot yet arbitrate the Hubble tension. Extending the TRGB data beyond the present ~1000 km/s, together with improved reconstructions of the local Universe, would reduce the field-to-field scatter well below the 5.2 km/s/Mpc we find here.
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BibTeX
@misc{stiskalek2026tworung,
title = {{Two-rung ladder: $H_0$ from Tip of the Red Giant Branch and geometric anchors alone}},
author = {Richard Stiskalek and Harry Desmond and Guilhem Lavaux},
howpublished = {HAL},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.29996},
eprint = {2609.29996},
archivePrefix = {arXiv},
url = {https://hal.science/hal-05830185v1},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Two-rung ladder: H_0 from Tip of the Red Giant Branch and geometric anchors alone
AU - Richard Stiskalek
AU - Harry Desmond
AU - Guilhem Lavaux
PY - 2026
DA - 2026/09/24
PB - HAL
DO - 10.48550/arxiv.2609.29996
UR - https://hal.science/hal-05830185v1
AB - We infer the Hubble constant H_0 from the ~400 Extragalactic Distance Database hosts with a tip of the red giant branch (TRGB) distance, calibrated on the geometric anchors of the Large Magellanic Cloud and NGC 4258. We forward-model the tip magnitudes and host redshifts including magnitude-limited selection, sky exposure, and density-dependent galaxy bias, conditioning on each of the 80 Manticore-Local realisations of the local density and peculiar-velocity fields in turn. As most hosts lie at cz_CMB ≲ 1000 km/s, where peculiar velocities are important, the inference is limited by the variance of these fields rather than by the TRGB calibration. For a fixed realisation, the redshift likelihood and density smoothing each move H_0 by less than 1 km/s/Mpc and a velocity monopole by 5.4 ± 3.4 km/s/Mpc, whereas the field-to-field scatter in H_0 is 5.2 km/s/Mpc. Weighting the posteriors from each realisation equally gives H_0 = 68.4 ± 5.9 km/s/Mpc, while weighting each by its Bayesian evidence gives 72.3 ± 2.6 km/s/Mpc. The latter value is set by a single particularly high-evidence realisation, making it sensitive to the finite sampling of the reconstruction posterior. This ladder therefore cannot yet arbitrate the Hubble tension. Extending the TRGB data beyond the present ~1000 km/s, together with improved reconstructions of the local Universe, would reduce the field-to-field scatter well below the 5.2 km/s/Mpc we find here.
ER -