Halo scaling relations and hydrostatic mass bias in the simba simulation from realistic mock X-ray catalogues

Abstract

We present a new end-to-end pipeline for Mock Observations of X-ray Halos and Analysis (MOXHA) for hydrodynamic simulations of massive halos, and use it to investigate X-ray scaling relations and hydrostatic mass bias in the Simba cosmological hydrodynamic simulation for halos with M500 ∼ 1013 − 15M⊙. MOXHA ties together existing yT-based software packages and adds new functionality to provide an end-to-end pipeline for generating mock X-ray halo data from large-scale or zoom simulation boxes. We compare MOXHA-derived halo properties in Simba to their emission-weighted counterparts, and forecast the systematic mass bias in mock Athena observations. Overall, we find inferred hydrostatic masses are biased low compared to true Simba values. For simple mass-weighting, we find $b_\text{MW} = 0.15^{+0.15}_{-0.14}$ ($16-84~{{\ \%}}$ range), while emission-weighting increases this to $b_\text{LW}=0.30^{+0.19}_{-0.10}$. The larger bias versus mass-weighted values we attribute to the spectroscopic and emission-weighted temperatures being biased systematically lower than mass-weighted temperatures. The full MOXHA pipeline recovers the emission-weighted hydrostatic masses at R500 reasonably well, yielding $b_\text{X}=0.33^{+0.28}_{-0.34}$. MOXHA-derived halo X-ray scalings are in very good agreement with observed scaling relations, with the inclusion of lower-mass groups significantly steepening the LX − M500, M500 − TX, and LX − TX relations. This indicates the strong effect the Simba feedback model has on low-mass halos, which strongly evacuates poor groups but still retains enough gas to reproduce observations. We find similar trends for analogous scaling relations measured at R500, as expected for halo-wide gas evacuation.

Surface Brightness Fluctuations in Two SPT Clusters: A Pilot Study

“…Numerical simulations which have estimated the hydrostatic mass bias have found average bias values of 0.1  b  0.3 (e.g., Nagai et al 2007;Lau et al 2009;Rasia et al 2012;Biffi et al 2016;Ruppin et al 2019;Gianfagna et al 2023;Jennings & Davé 2023). However, they all find that the hydrostatic mass bias will have a distribution (and will also depend on the radius or density contrast at which the mass is being measured), and nearly all of these studies find that for an individual cluster, the bias for M 500 can be close to zero, and in some cases even negative.…”