Measuring $H_0$ using X-ray and SZ effect observations of dynamically relaxed galaxy clusters

TL;DR

This study estimates the Hubble Constant using X-ray and SZ observations of relaxed galaxy clusters, highlighting the impact of calibration uncertainties and potential improvements for more precise future measurements.

Contribution

First analysis to marginalize over empirical X-ray temperature calibration uncertainties in H_0 measurement using galaxy clusters.

Findings

Estimated H_0 = 67.3^{+21.3}_{-13.3} km/s/Mpc with current data.

Intrinsic scatter in pressure ratio is about 13%, mainly due to cluster triaxiality.

Calibration improvements could enable percent-level precision in H_0 measurement.

Abstract

We use a sample of 14 massive, dynamically relaxed galaxy clusters to constrain the Hubble Constant, $H_0$, by combining X-ray and Sunyaev-Zel'dovich (SZ) effect signals measured with Chandra, Planck and Bolocam. This is the first such analysis to marginalize over an empirical, data-driven prior on the overall accuracy of X-ray temperature measurements, while our restriction to the most relaxed, massive clusters also minimizes astrophysical systematics. For a cosmological-constant model with $\Omega_m = 0.3$ and $\Omega_{\Lambda} = 0.7$, we find $H_0 = 67.3^{+21.3}_{-13.3}$ km/s/Mpc, limited by the temperature calibration uncertainty (compared to the statistically limited constraint of $H_0 = 72.3^{+7.6}_{-7.6}$ km/s/Mpc). The intrinsic scatter in the X-ray/SZ pressure ratio is found to be $13 \pm 4$ per cent ($10 \pm 3$ per cent when two clusters with significant galactic dust emission are removed from the sample), consistent with being primarily due to triaxiality and projection. We discuss the prospects for reducing the dominant systematic limitation to this analysis, with improved X-ray calibration and/or precise measurements of the relativistic SZ effect providing a plausible route to per cent level constraints on $H_0$.