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 Haloes and Analysis (moxha) for hydrodynamic simulations of massive haloes, and use it to investigate X-ray scaling relations and hydrostatic mass bias in the simba cosmological hydrodynamic simulation for haloes 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 bMW = 0. 15^+0. 15-₀. ₁₄ (16–84 per cent range), while emission-weighting increases this to bLW=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 bX=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 haloes, 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.