Abstract
The gas depletion factor gamma (z), i.e., the average ratio of the gas mass fraction to the cosmic mean baryon fraction of galaxy clusters, plays a very important role in the cosmological application of the gas mass fraction measurements. In this paper, using the newest catalog of 182 galaxy clusters detected by the Atacama Cosmology Telescope (ACT) Polarization experiment, we investigate the possible redshift evolution of gamma (z) through a new cosmology-independent method. The method is based on non-parametric reconstruction using the measurements of Hubble parameters from cosmic chronometers. Unlike hydrodynamical simulations suggesting constant depletion factor, our results reveal the trend of gamma (z) decreasing with redshift. This result is supported by a parametric model fit as well as by calculations on the reduced ACTPol sample and on the alternative sample of 91 SZ clusters reported earlier in ACT compilation. Discussion of possible systematic effects leaves an open question about validity of the empirical relation M_{tot}–f_{gas} obtained on very close clusters. These results might pave the way to explore the hot gas fraction within large radii of galaxy clusters as well as its possible evolution with redshift, which should be studied further on larger galaxy cluster samples in the upcoming X-ray/SZ cluster surveys.
Highlights
Some problems arise when one uses fgas observations as a cosmological tool, for instance, the assumption that the gas mass fraction evolves little or does not evolve at all
The derived fgas values should be calibrated with the baryon depletion factor γ, the ratio by which the baryon fraction of galaxy clusters is depleted with respect to the universal mean of baryon fraction [17]
Using a set of hydrodynamical simulations of galaxy clusters characterized by different physical processes, Planelles et al [23] explored how the fraction and spatial distribution of baryons, are affected by the feedback from supernova (SN) and active galactic nuclei (AGN) within R500 and R2500
Summary
Some problems arise when one uses fgas observations as a cosmological tool, for instance, the assumption that the gas mass fraction evolves little or does not evolve at all. The derived fgas values should be calibrated with the baryon depletion factor γ , the ratio by which the baryon fraction of galaxy clusters is depleted with respect to the universal mean of baryon fraction [17]. M500 denotes the total mass within R500, the radius inside which the mass density is 500 times the critical density of the universe Their results suggested the depletion factor inside R500 quantified with γ0 = 0.85 ± 0.03 and γ1 = 0.02 ± 0.07, which indicated that at z < 1 the gas mass fraction at intermediate to large cluster radii should have small cluster-to-cluster scatter and should not evolve with redshift. With the combination of gas mass fraction obtained from X-ray measurements [26] and angular diameter distances from SZ effect/X-ray measurements, Holanda [27] found a mild redshift evolution of the depletion factor
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