Non-parametric estimation of the baryon gas fraction and the cosmological bias with clusters

TL;DR

This paper introduces a model-independent approach to estimate the baryon gas fraction in galaxy clusters and its evolution, using supernova data to understand biases affecting cosmological measurements.

Contribution

It develops a framework that combines supernova data and iterative smoothing to quantify the evolution of hydrostatic mass bias without relying on specific models.

Findings

Bias evolves with time to match CMB constraints

Results confirm previous findings on gas fraction evolution

Method provides a way to disentangle astrophysical and cosmological effects

Abstract

X-ray observations of galaxy clusters allow us to estimate the gas fraction, and thus the baryon fraction, and its evolution over time. This offers an additional cosmological probe as well as a probe of the gas behaviour in massive halos at the end of structure formation. However, cosmological and astrophysical effects are degenerate, and both should be modeled in order to explain observations; otherwise, the chosen baryonic model can potentially bias the cosmological results. We propose to quantify this effect by adopting a model-independent framework. We utilize Type Ia Supernovae to reconstruct the cosmic expansion history and apply the iterative smoothing method to infer the mass and redshift evolution of the hydrostatic mass bias. Our results confirm previous findings and show that the bias should evolve with time to reproduce CMB cosmological constraints.