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Seven Problems with the Claims Related to the Hubble Tension in arXiv:1810.02595

Adam G. Riess, Stefano Casertano, D'Arcy Kenworthy, Dan Scolnic, Lucas Macri

TL;DR

The paper investigates the two claims that Gaia DR2 Cepheid parallaxes and a local cosmic void could reconcile the local $H_0$ with Planck $H_0$ within $\Lambda$CDM. It dissects seven errors in Shanks et al. 2018—five tied to Claim A and two to Claim B—arguing that corrected data sustain the Cepheid-based $H_0$ around $73.5 \pm 1.4$ and remain inconsistent with Planck's $H_0$ of $67.4 \pm 0.5$. The critique emphasizes that the Gaia parallax zeropoint offset is magnitude/color dependent and must be treated with proper uncertainty, and that independent anchors from LMC DEBs and NGC 4258 masers secure the distance scale. It then shows that SN data strongly disfavour a local hole, with $\Delta\chi^2 = 11.5$ ($3.4\sigma$) exclusion, and higher significance with additional SN samples, implying no viable local-void solution to the Hubble tension.

Abstract

Shanks et al. (2018) arXiv:1810.02595 make two claims that they argue bring the local measurement and early Universe prediction of H0 into agreement: A) they claim that Gaia DR2 parallax measurements show the geometric calibration of the Cepheid distance scale used to measure H0 to be grossly in error and B) that we live near the middle of an enormous void, further biasing the local measurement of the Hubble constant. We show that the first claim is caused by five erroneous uses of the data: in decreasing order of importance: 1) the use of a distance indicator, main sequence fitting of cluster stars, which is unrelated to the calibration of Cepheids and therefore has no bearing on current measurements of H0; 2) the use of Gaia data for Cepheids that fully saturate the detector, producing unreliable parallaxes; 3) the use of a fixed parallax offset which is known to depend on source magnitude and color but which is derived for sources with extremely different colors and magnitudes; 4) ignoring the uncertainty in this offset; and 5) ignoring the other geometric sources of Cepheid calibration, the distance of the LMC from detached eclipsing binaries and the masers in NGC 4258, which are independent of Milky Way parallaxes. Just resolving the first two of these issues by not using unrelated or saturated data leads to no inconsistency between Gaia parallaxes and the current Cepheid distance scale. The second claim can be refuted 6) because of the increase in chi-squared that the alleged void would entail in SN measurements in the Hubble flow, and 7) because it would represent a 6 sigma fluctuation of cosmic variance between the local and globally measured expansion, requiring us to live in an exceedingly special location.

Seven Problems with the Claims Related to the Hubble Tension in arXiv:1810.02595

TL;DR

The paper investigates the two claims that Gaia DR2 Cepheid parallaxes and a local cosmic void could reconcile the local with Planck within CDM. It dissects seven errors in Shanks et al. 2018—five tied to Claim A and two to Claim B—arguing that corrected data sustain the Cepheid-based around and remain inconsistent with Planck's of . The critique emphasizes that the Gaia parallax zeropoint offset is magnitude/color dependent and must be treated with proper uncertainty, and that independent anchors from LMC DEBs and NGC 4258 masers secure the distance scale. It then shows that SN data strongly disfavour a local hole, with () exclusion, and higher significance with additional SN samples, implying no viable local-void solution to the Hubble tension.

Abstract

Shanks et al. (2018) arXiv:1810.02595 make two claims that they argue bring the local measurement and early Universe prediction of H0 into agreement: A) they claim that Gaia DR2 parallax measurements show the geometric calibration of the Cepheid distance scale used to measure H0 to be grossly in error and B) that we live near the middle of an enormous void, further biasing the local measurement of the Hubble constant. We show that the first claim is caused by five erroneous uses of the data: in decreasing order of importance: 1) the use of a distance indicator, main sequence fitting of cluster stars, which is unrelated to the calibration of Cepheids and therefore has no bearing on current measurements of H0; 2) the use of Gaia data for Cepheids that fully saturate the detector, producing unreliable parallaxes; 3) the use of a fixed parallax offset which is known to depend on source magnitude and color but which is derived for sources with extremely different colors and magnitudes; 4) ignoring the uncertainty in this offset; and 5) ignoring the other geometric sources of Cepheid calibration, the distance of the LMC from detached eclipsing binaries and the masers in NGC 4258, which are independent of Milky Way parallaxes. Just resolving the first two of these issues by not using unrelated or saturated data leads to no inconsistency between Gaia parallaxes and the current Cepheid distance scale. The second claim can be refuted 6) because of the increase in chi-squared that the alleged void would entail in SN measurements in the Hubble flow, and 7) because it would represent a 6 sigma fluctuation of cosmic variance between the local and globally measured expansion, requiring us to live in an exceedingly special location.

Paper Structure

This paper contains 3 sections, 1 figure.

Table of Contents

  1. Introduction
  2. Claim A: The Geometric Calibration of the Distance Ladder
  3. Claim B: The Local Hole

Figures (1)

  • Figure 1: Astrometric and photometric parallax comparison for the 632 Milky Way Cepheids that Gaia classifies as Fundamental mode, Delta-Cepheii type, not in the LMC or SMC or those in the secondary sequence $\sim$5 mag fainter. The Wesenheit magnitudes madore82 are calculated from Gaia G, Bp, and Rp magnitudes regressing with Cepheids in common with HST system magnitudes Riess:2018b to derive transformations between the photometric systems. The absolute photometric parallaxes are on the Riess:2016 Cepheid distance scale. The Gaia DR2 parallaxes do not include the parallax zeropoint offset which must be added to calibrate Gaia parallaxes Lindegren:2018 and which is known to depend on source magnitude and color Lindegren:2018. As shown, the offset for 46 Milky Way Cepheids from Riess:2018b is -46 $\pm 13$$\mu$as (red line) and larger for the brightest Cepheids, consistent with the bright end of the QSO's (blue line), Red Giants Zinn:2018 and Cepheids on the HST system Riess:2018b but clearly larger than the mean of $-29$$\mu$as (green line), derived from the mean QSO which is bluer and much fainter ($G\sim19$) mag than Cepheids. The Cepheids are binned for easy comparison. Shanks:2018 has assumed the offset from the median QSO for the 7 HST Cepheids with mean $G=9$ mag Riess:2018a which is in poor agreement with the 632 Cepheids and the bright end of the QSO's producing an offset in the calculated distance scale.