Systematic Errors in the Hubble Constant Measurement from the Sunyaev-Zel'dovich effect

TL;DR

This paper investigates the causes of systematic underestimation of the Hubble constant derived from the Sunyaev-Zel'dovich effect and X-ray observations, identifying key sources of error through models and simulations.

Contribution

It provides a detailed analysis of the physical origins of systematic errors in Hubble constant measurements from the SZ effect, highlighting the roles of ICM inhomogeneities and cluster shape.

Findings

Density and temperature inhomogeneities cause temperature measurement bias.

Asphericity and departures from isothermality contribute to systematic errors.

The identified systematics explain observed biases and dispersions in measurements.

Abstract

The Hubble constant estimated from the combined analysis of the Sunyaev-Zel'dovich effect and X-ray observations of galaxy clusters is systematically lower than those from other methods by 10-15 percent. We examine the origin of the systematic underestimate using an analytic model of the intracluster medium (ICM), and compare the prediction with idealistic triaxial models and with clusters extracted from cosmological hydrodynamical simulations. We identify three important sources for the systematic errors; density and temperature inhomogeneities in the ICM, departures from isothermality, and asphericity. In particular, the combination of the first two leads to the systematic underestimate of the ICM spectroscopic temperature relative to its emission-weighed one. We find that these three systematics well reproduce both the observed bias and the intrinsic dispersions of the Hubble constant estimated from the Sunyaev-Zel'dovich effect.