New constraints on anisotropic expansion from supernovae Type Ia. Issue 1 (3rd May 2022)

• Record Type: Journal Article
• Authors: Rahman, W; Trotta, R; Boruah, S S; Hudson, M J; van Dyk, D A
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 514:Issue 1(2022)
• Page Start: 139
• Page End: 163
• Publication Date: 2022-05-03
• Subjects: methods: statistical -- supernovae: general -- cosmological parameters -- cosmology: observations -- dark energy; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1223
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We re-examine the contentious question of constraints on anisotropic expansion from Type Ia supernovae (SNIa) in the light of a novel determination of peculiar velocities, which are crucial to test isotropy with SNe out to distances ⪝200 h -1 Mpc. We re-analyse the Joint Light-Curve Analysis (JLA) Supernovae (SNe) data, improving on previous treatments of peculiar velocity corrections and their uncertainties (both statistical and systematic) by adopting state-of-the-art flow models constrained independently via the 2M++ galaxy redshift compilation. We also introduce a novel procedure to account for colour-based selection effects, and adjust the redshift of low- z SNe self-consistently in the light of our improved peculiar velocity model. We adopt the Bayesian hierarchical model BAHAMAS to constrain a dipole in the distance modulus in the context of the Lambda cold dark matter (ΛCDM) model and the deceleration parameter in a phenomenological Cosmographic expansion. We do not find any evidence for anisotropic expansion, and place a tight upper bound on the amplitude of a dipole, | D μ | < 5.93 × 10 −4 (95 per cent credible interval) in a ΛCDM setting, and $|D_{q_0}| \lt 6.29 \times 10^{-2}$ in the Cosmographic expansion approach. Using Bayesian model comparison, we obtain posterior odds in excess of 900:1 (640:1) against a constant-in-redshift dipole for ΛCDM (the Cosmographic expansion). In the isotropic case, an accelerating universe is favoured with odds of ∼1100:1 with respect to a decelerating one.