Forward-modelling Milky Way Cepheids: selection effects and physical priors in the Gaia-HST calibration
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| Autores principales: | , , , , |
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| Formato: | Preprint |
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2026
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| _version_ | 1866908877158612992 |
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| author | Stiskalek, Richard Riess, Adam Desmond, Harry Lavaux, Guilhem Scolnic, Dan |
| author_facet | Stiskalek, Richard Riess, Adam Desmond, Harry Lavaux, Guilhem Scolnic, Dan |
| contents | The advent of high-precision Gaia parallaxes for Milky Way Cepheids enables per cent-level calibration of the local distance ladder and $H_0$. We revisit the Milky Way Cepheid calibration from Gaia EDR3 parallaxes using a fully forward-modelled Bayesian framework that simultaneously infers the period--luminosity relation, the Gaia parallax zero-point offset, and individual stellar distances while explicitly incorporating the disk geometry of the Galaxy through the distance prior and the selection functions specified in two distinct HST SH0ES campaigns. We derive an analytic treatment of the detection probability that accounts for magnitude, parallax, period, and extinction cuts and reduces the selection treatment to a tractable integral over distance and sky position. Posterior predictive checks show that this generative model matches well the observed distributions of parallaxes, magnitudes, and periods. Modelling Galactic structure and survey truncation self-consistently in a Bayesian framework yields period--luminosity parameters that agree with the SH0ES maximum-likelihood values at the ${<}0.5\,σ$ level, a consequence, we show, of the small intrinsic scatter of the Cepheid period--luminosity relation. Adopting, as recently advocated, a uniform-in-volume prior without simultaneously accounting for selection leads to a ${\sim}\,0.05~\mathrm{mag}$ bias in the period--luminosity zero-point and posterior predictive distributions incompatible with the observed data; this shift is mostly driven by the omission of the selection model. A consistent Bayesian treatment of Galactic structure and selection effects reinforces the local distance-ladder determination of $H_0$, and hence the Hubble tension with early-Universe inferences. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2603_09880 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Forward-modelling Milky Way Cepheids: selection effects and physical priors in the Gaia-HST calibration Stiskalek, Richard Riess, Adam Desmond, Harry Lavaux, Guilhem Scolnic, Dan Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics The advent of high-precision Gaia parallaxes for Milky Way Cepheids enables per cent-level calibration of the local distance ladder and $H_0$. We revisit the Milky Way Cepheid calibration from Gaia EDR3 parallaxes using a fully forward-modelled Bayesian framework that simultaneously infers the period--luminosity relation, the Gaia parallax zero-point offset, and individual stellar distances while explicitly incorporating the disk geometry of the Galaxy through the distance prior and the selection functions specified in two distinct HST SH0ES campaigns. We derive an analytic treatment of the detection probability that accounts for magnitude, parallax, period, and extinction cuts and reduces the selection treatment to a tractable integral over distance and sky position. Posterior predictive checks show that this generative model matches well the observed distributions of parallaxes, magnitudes, and periods. Modelling Galactic structure and survey truncation self-consistently in a Bayesian framework yields period--luminosity parameters that agree with the SH0ES maximum-likelihood values at the ${<}0.5\,σ$ level, a consequence, we show, of the small intrinsic scatter of the Cepheid period--luminosity relation. Adopting, as recently advocated, a uniform-in-volume prior without simultaneously accounting for selection leads to a ${\sim}\,0.05~\mathrm{mag}$ bias in the period--luminosity zero-point and posterior predictive distributions incompatible with the observed data; this shift is mostly driven by the omission of the selection model. A consistent Bayesian treatment of Galactic structure and selection effects reinforces the local distance-ladder determination of $H_0$, and hence the Hubble tension with early-Universe inferences. |
| title | Forward-modelling Milky Way Cepheids: selection effects and physical priors in the Gaia-HST calibration |
| topic | Astrophysics of Galaxies Cosmology and Nongalactic Astrophysics |
| url | https://arxiv.org/abs/2603.09880 |