Peculiar velocity effects on the Hubble constant from time-delay cosmography

Abstract

Two major challenges of contemporary cosmology are the Hubble tension and the cosmic dipole tension. At the crossroad of these, we investigate the impact of peculiar velocities on estimations of the Hubble constant from time-delay cosmography. We quantify the bias on the inference of the Hubble constant due to peculiar velocities of the lens, the source and of the observer. The former two, which may cancel from one system to another, affect the determination of the angular diameter distances in the time-delay formula, and reconstructed quantities like the angle to the source, via a lens model. On the other hand, the peculiar velocity of the observer, which is a debated quantity in the context of the cosmic dipole tension, systematically affects observed angles through aberration, redshifts, angular diameter distance and reconstructed quantities. We compute in detail the effect of these peculiar velocities on the inference of the Hubble constant to linear order in the peculiar velocities for the seven lenses of the H0LiCOW/TDCOSMO collaboration. The bias generated by the observer's peculiar velocity alone can reach $1.15\%$ for the lenses which are well aligned with it. This results in a $0.25\%$ bias for the seven combined lenses. Assuming a typical peculiar velocity of $300$ km s${}^{-1}$ for the lens and the source galaxies, these add an additional random uncertainty, which can reach $1\%$ for an individual lens, but reduces to $0.24\%$ for the full TDCOSMO sample. The picture may change if peculiar velocities turn out to be larger than expected. Any time-delay cosmography program which aims for percent precision on the Hubble constant may need to take this source of systematic bias into account. This is especially so for future ground-based surveys which cover a fraction of the celestial sphere that is well aligned with the observer's peculiar velocity.

19 pages, 8 figures, 2 tables, online version adapted to make it consistent with published version

References in corpus (12)

• A Comprehensive Measurement of the Local Value of the Hubble Constant with 1 km/s/Mpc Uncertainty from the Hubble Space Telescope and the SH0ES Team
• Large Magellanic Cloud Cepheid Standards Provide a 1% Foundation for the Determination of the Hubble Constant and Stronger Evidence for Physics Beyond LambdaCDM
• Is the Observable Universe Consistent with the Cosmological Principle?
• H0LiCOW IV. Lens mass model of HE 0435-1223 and blind measurement of its time-delay distance for cosmology
• A Challenge to the Standard Cosmological Model
• Anomalies in Physical Cosmology
• Over-constrained Gravitational Lens Models and the Hubble Constant
• Directional Variations of Cosmological Parameters from the Planck CMB Data
• The need for accurate redshifts in supernova cosmology
• Do supernovae indicate an accelerating universe?
• Statistical effects of the observer's peculiar velocity on source number counts
• Sample Variance for Supernovae Distance Measurements and the Hubble tension

Cited by in corpus (1)

• TDCOSMO 2025: Cosmological constraints from strong lensing time delays