Satellite fraction of early-type galaxies and its evolution for intrinsic-alignment modeling

Determine the satellite fraction of early-type galaxies in the KiDS-Legacy weak-lensing source sample and characterize how this fraction evolves with host halo mass and redshift, so that intrinsic-alignment signals of central and satellite galaxies can be modeled separately and accurately in the Non-Linear Alignment mass-dependent (NLA-M) framework.

Background

The KiDS-Legacy analysis introduces a galaxy-type and mass-dependent intrinsic-alignment (IA) model (NLA-M) that scales IA amplitude with the fraction of early-type galaxies and their average host halo mass in each tomographic bin. Satellite and central galaxies likely have different IA mechanisms and scalings, but the satellite fraction within the early-type population is not measured for the KiDS-Legacy source sample.

The authors note that the satellite fraction almost certainly evolves with halo mass and redshift, and that most calibration samples used to constrain IA also lack robust satellite-fraction measurements. Without these measurements, IA signals must be treated effectively and jointly, limiting the fidelity of small-scale IA modeling and potentially affecting cosmological inferences. Establishing the satellite fraction and its evolution would enable a more accurate separation of IA contributions from centrals and satellites in cosmic shear analyses.