Inspecting the Cepheid Distance Ladder: the Hubble Space Telescope Distance to the SN Ia Host Galaxy NGC 5584

Behnam Javanmardi,Alexandre Gallenne,Antoine Mérand,Wolfgang Gieren,Pierre Kervella,Simon Borgniet,Vincent Hocdé,Grzegorz Pietrzyński,Louise Breuval,Nicolas Nardetto

doi:10.3847/1538-4357/abe7e5

Abstract

Abstract The current tension between the direct and the early-universe measurements of the Hubble constant, H 0, requires detailed scrutiny of all the data and methods used in the studies on both sides of the debate. The Cepheids in the Type Ia supernova (SN Ia) host galaxy NGC 5584 played a key role in the local measurement of H 0. The SH0ES project used the observations of this galaxy to derive a relation between the Cepheids’ periods and ratios of their amplitudes in different optical bands of the Hubble Space Telescope and used these relations to analyze the light curves of the Cepheids in around half of the current sample of local SN Ia host galaxies. In this work, we present an independent detailed analysis of the Cepheids in NGC 5584. We employ different tools for our photometric analysis and a completely different method for our light-curve analysis, and we do not find a systematic difference between our period and mean magnitude measurements compared to those reported by SH0ES. By adopting a period–luminosity relation calibrated by the Cepheids in the Milky Way, we measure a distance modulus μ = 31.810 ± 0.047 (mag), which is in agreement with μ = 31.786 ± 0.046 (mag) measured by SH0ES. In addition, the relations we find between the periods and amplitude ratios of the Cepheids in NGC 5584 are significantly tighter than those of SH0ES, and their potential impact on the direct H 0 measurement will be investigated in future studies.

Highlights

The current expansion rate of the universe, known as the Hubble constant or H0, is one of the fundamental parameters of the standard model of cosmology and of any viable cosmological model
The distance to a nearby SN Ia host galaxy can be measured by obtaining the relation between the pulsation period and WH of its identified Cepheids, and by adopting a WH versus period relation calibrated by the Cepheids in, e.g., the Milky Way (MW) or the Large Magellanic Cloud (LMC)
NGC 5584 played a key role in the direct measurement of H0 from the Cepheid distance ladder by the SH0ES team (Riess et al 2016)

Summary

Introduction

The current expansion rate of the universe, known as the Hubble constant or H0, is one of the fundamental parameters of the standard model of cosmology and of any viable cosmological model. The debate was settled after the findings of the Hubble Space Telescope (HST) H0 Key Project, whose final result was H0 = 72 ± 8 km s−1 Mpc−1 (Freedman et al 2001). This value was found to be in agreement with the subsequent results from the observations of the cosmic microwave background (CMB) by the Wilkinson Microwave Anisotropy Probe (WMAP; e.g., Spergel et al 2003) based on the standard Lambda-cold-darkmatter (ΛCDM) model.

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