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arXiv · 2504.01076

The SRG/eROSITA All-Sky Survey. The Weak-Lensing Mass Calibration and the Stellar Mass-to-Halo Mass Relation from the Hyper Suprime-Cam Subaru Strategic Program

I-Non Chiu·Vittorio Ghirardini·Sebastian Grandis·Nobuhiro Okabe·Emmanuel Artis·Esra Bulbul·Y. Emre Bahar·Fabian Balzer·Nicolas Clerc·Johan Comparat·Bau-Ching Hsieh·Florian Kleinebreil·Matthias Kluge·Ang Liu·Rogerio Monteiro-Oliveira·Masamune Oguri·Florian Pacaud·Miriam Ramos Ceja·H. Thomas Reiprich·Jeremy Sanders·Tim Schrabback·Riccardo Seppi·Martin Sommer·Sut-Ieng Tam·Keiichi Umetsu·Xiaoyuan Zhang
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Abstract

We present the weak-lensing mass calibration and constrain the BCG (brightest cluster galaxy) stellar-mass-to-halo-mass-and-redshift ($M_{\star,\mathrm{BCG}}-M-z$) relation for a sample of $124$ galaxy clusters and groups at redshift $0.1<z<0.8$ from the first Data Release of the $eROSITA$ All-Sky Survey (eRASS1), using data from the Hyper Suprime-Cam (HSC) Subaru Strategic Program. The cluster survey is conducted by the $eROSITA$ X-ray telescope aboard the Spectrum-Roentgen-Gamma (SRG) space observatory. The cluster sample is X-ray-selected and optically confirmed with a negligibly low contamination rate ($\approx5%$). On a basis of individual clusters, the shear profiles of $96$ clusters are derived using the HSC Three-Year (HSC-Y3) weak-lensing data, while the BCG stellar masses of $101$ clusters are estimated using the SED template fitting to the HSC five-band ($grizY$) photometry. The observed X-ray photon count rate is used as the mass proxy, based on which individual halo masses are obtained at the given count rate in a population modelling while accounting for systematic uncertainties in the weak-lensing modelling through a simulation-calibrated weak-lensing mass-to-halo-mass relation. The count rate and BCG stellar mass relations are simultaneously constrained in a forward and population modelling. In agreement with the results based on the weak-lensing data from the DES and KiDS surveys, we obtain a count rate relation with a self-similar redshift scaling and a mass trend that is steeper than the self-similar prediction. Our results suggest that the BCG stellar mass at a fixed halo mass has remained stable with a moderate increase at a level of $\left(20\pm8\right)%$ since redshift $z\approx0.8$. This finding supports the picture of the ``rapid-then-slow'' BCG formation, where the majority of the stellar mass must have been assembled at much earlier cosmic time.

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I-Non Chiu, Vittorio Ghirardini, Sebastian Grandis, Nobuhiro Okabe, Emmanuel Artis, Esra Bulbul, Y. Emre Bahar, Fabian Balzer, Nicolas Clerc, Johan Comparat, Bau-Ching Hsieh, Florian Kleinebreil, Matthias Kluge, Ang Liu, Rogerio Monteiro-Oliveira, Masamune Oguri, Florian Pacaud, Miriam Ramos Ceja, H. Thomas Reiprich, Jeremy Sanders, Tim Schrabback, Riccardo Seppi, Martin Sommer, Sut-Ieng Tam, Keiichi Umetsu, Xiaoyuan Zhang. 2025-09-18. The SRG/eROSITA All-Sky Survey. The Weak-Lensing Mass Calibration and the Stellar Mass-to-Halo Mass Relation from the Hyper Suprime-Cam Subaru Strategic Program. https://doi.org/10.1051/0004-6361%2F202554942

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