Oral Presentation

Toward Precision X-ray Stacking of Low-Mass Galaxy Clusters: Methods and Application to eROSITA

Author(s): Yukana Tsujita, Naomi Ota, Nhan Nguyen (Nara Women’s University), Florian Pacaud, Thomas Reiprich (Universität Bonn), Miriam Ramos Ceja, Jeremy Sanders, Esra Bulbul (MPE), Nobuhiro Okabe (Hiroshima University), Masamune Oguri (Chiba University), Satoshi Miyazaki (NAOJ), Ikuyuki Mitsuishi (Nagoya University)

Presenter: Yukana Tsujita (Nara Women's University)

Low-mass galaxy clusters (with masses of $10^{13}-10^{14} M_\odot$) are key tracers of the hierarchical growth of cosmic structure. However, their low X-ray luminosities often make individual detections challenging, necessitating the use of statistical techniques such as stacking. The eROSITA all-sky survey provides a large sample of such faint systems, but accurate estimation of their average X-ray properties requires careful treatment. In our previous study (Nguyen et al. subm), we validated a count-rate-based stacking method using mock eROSITA observations of ~1000 clusters in the eFEDS field. In this work, we extend that approach by incorporating hardness ratio (HR)-based gas temperature estimates, enabling a physically consistent conversion to intrinsic luminosities. We apply the method to ~5900 clusters in the eRASS:4 field selected from the the Subaru HSC-based CAMIRA optical cluster catalog over the redshift range 0.1< z < 1.4, and derive T–N and L–N scaling relations. We also evaluate systematic uncertainties related to HR distributions and weighting schemes. As a next step, we aim to compare the results with weak-lensing masses to calibrate the mass-luminosity relation, ultimately contributing to future cluster cosmology.