The signature of major mergers on the hydrostatic mass bias of galaxy clusters

Isac Barranco-Llorca; David Vallés-Pérez; Susana Planelles; Vicent Quilis

doi:10.1051/0004-6361/202556598

paper

The signature of major mergers on the hydrostatic mass bias of galaxy clusters

arXiv:2511.10730 · doi:10.1051/0004-6361/202556598

Abstract

While galaxy cluster masses are fundamental cosmological observables, estimates based on intra-cluster medium observations rely on hydrostatic equilibrium, introducing a systematic bias. We investigate how mergers drive the time evolution of this hydrostatic mass bias, identifying the dominant physical mechanisms and their dependence on dynamical state and merger history. Using a high-resolution AMR Eulerian+ $N$ -body cosmological simulation, we analyse a sample of cluster mergers within $1.5 \leq z \leq 0$ , comparing true and hydrostatic masses derived from gas density and temperature profiles, and tracing their evolution. At $z = 0$ , the hydrostatic mass bias shows a mild correlation with dynamical state. During major mergers, the bias follows a characteristic trend: a sharp negative dip around the merger time, a transient positive peak, and a gradual return to pre-merger levels. This behaviour is primarily driven by morphological and dynamical reconfigurations of the gas density within the ICM, while thermodynamical processes play a secondary role. The pattern shows no strong dependence on secondary parameters, such as mass ratio or impact parameter, but it can be fitted to a simple time-dependent functional form. This trend is present at radii $r \leq R_{vir}$ , although with reduced amplitude and shorter timescales as the radius decreases. Hydrostatic mass bias is closely linked, albeit in a non-trivial way, with the merging history of galaxy clusters. We find that the bias values are weakly correlated with the dynamical state of clusters. Nevertheless, our results give a robust estimation of the hydrostatic mass bias values in the pre-merger, merging, and post-merger phases. These findings highlight the importance of delving deeper into the observational assessment of cluster assembly state in order to improve mass estimations for cosmological analyses.

arXiv comment14 pages, 10 figures (+ one appendix: 1 page, 1 figure). Proposed for acceptance in Astronomy & Astrophysics. Abstract shortened for publication in ArXiv

The signature of major mergers on the hydrostatic mass bias of galaxy clusters

Abstract

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