Halo Scaling Relations and Hydrostatic Mass Bias in the Simba Simulation From Realistic Mock X-ray Catalogues

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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 ∼ 1013−15 𝑀⊙ . 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% 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 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.

Reference: Halo Scaling Relations and Hydrostatic Mass Bias in the Simba Simulation From Realistic Mock X-ray Catalogues, Fred Jennings, Romeel Davé, submitted to MNRAS,  arXiv:2306.01397