Oral Presentation

Studying the galaxy populations of eROSITA X-ray-selected galaxy clusters

Author(s): I-Non Chiu (National Cheng Kung University)

Presenter: I-Non Chiu (National Cheng Kung University)

In this talk, I will present studies of the galaxy populations within galaxy clusters selected by the eROSITA telescope in X-rays, using optical data sets from the Hyper Suprime-Cam Subaru (HSC) Strategic Program.

The first part of the talk focuses on the sample in the first Data Release of the eROSITA All-Sky Survey (eRASS1). We perform the weak-lensing mass calibration of 124 galaxy clusters and groups at redshift 0.1 < z < 0.8 and constrain their BCG (brightest cluster galaxy) stellar-mass-to-halo-mass-and-redshift
(M⋆,BCG–M–z) relation. On the basis of individual clusters, the shear profiles g+ of the clusters are derived using the HSC Three-Year (HSC-Y3) weak-lensing data, while their BCG stellar masses M⋆,BCG are estimated using SED template fitting to the HSC five-band (grizY) photometry. Our results suggest that the BCG stellar mass at a fixed halo mass has remained stable with a moderate increase at a level of (20±8)% since redshift z ≈ 0.8. 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.

In the second part, we measure the radial distribution and the luminosity function of ~500 galaxy clusters selected in the eROSITA Final Equatorial-Depth Survey (eFEDS), conducted in the verification phase prior to the main eRASS survey. We discuss the results and make cosmological applications to cluster selection using weak gravitational lensing.