The Measurement of the Splash-back Radius of Dark Matter Halos

Abstract In the hierarchical evolution framework of cosmology, larger halos grow through matter accretion and halo mergers. To clarify halo evolution, we need to define the halo mass and radius physically. However, the pseudoevolution problem makes the process difficult. Thus, we aim to measure the splash-back radius ( R sp ), a physically defined halo radius for a large number of halos with various mass and redshift, and to determine the most important parameters that affect it. We use the typical definition of splash-back radius as the radius with the steepest radial density profile. In this work, we measure the splash-back radius of dark matter halos within the mass of 10 13 M ⊙ to 3 × 10 15 M ⊙ and redshifts spanning 0.08–0.65. This is the measurement of the R sp in the largest range of halo mass and redshift. Using the shear catalog of the Dark Energy Camera Legacy Survey Data Release 8, we investigate the splash-back radius of halos associated with galaxies and galaxy clusters identified in the various catalogs. Our finding reveals a trend wherein massive halos demonstrate a larger splash-back radius, and the normalized splash-back radius ( R sp / R 200m ) shows a U-shaped mass evolution. The upturn in these relations mainly comes from the contribution of massive halos with low redshifts. We further find the splash-back radius increases with the peak height, while the normalized splash-back radius has a negative relation with the peak height. We also find that R sp ≳ R 200m for most halos, indicating their low accretion rates. Our result is consistent with previous literature across a wide range of mass, redshift, and peak height, as well as the simulation work from More et al.