The eROSITA Final Equatorial-Depth Survey (eFEDS) - Splashback radius of X-ray galaxy clusters using galaxies from HSC survey

We present the splashback radius measurements around the SRG/eROSITA eFEDS X-ray selected galaxy clusters by cross-correlating them with HSC S19A photometric galaxies. The X-ray selection is expected to be less affected by systematics related to projection that affects optical cluster finder algorithms. We use a nearly volume-limited sample of 109 galaxy clusters selected in 0.5-2.0 keV band having luminosity L_X > 10^43.5 erg s⁻¹ h⁻² within the redshift z < 0.75 and obtain measurements of the projected cross-correlation with a signal to noise of 17.43. We model our measurements to infer a 3D profile and find that the steepest slope is sharper than −3 and associate the location with the splashback radius. We infer the value of the 3D splashback radius r_sp = 1.45⁺₋₀⁰₂₆³⁰ h⁻¹ Mpc. We also measure the weak-lensing signal of the galaxy clusters and obtain halo mass log[M_200m/h⁻¹ M_☉] = 14.52 ± 0.06 using the HSC-S16A shape catalogue data at the median redshift z = 0.46 of our cluster sample. We compare our r_sp values with the spherical overdensity boundary r_200m = 1.75 ± 0.08 h⁻¹ Mpc based on the halo mass, which is consistent within 1.2σ with the ЛCDM predictions. Our constraints on the splashback radius, although broad, are the best measurements thus far obtained for an X-ray selected galaxy cluster sample.