A dark matter halo has traditionally been viewed as a virialized structure bounded by its virial radius. However, the growth of a halo means it is inevitably surrounded by a non-virialized envelope of freshly accreted material. Failing to account for this envelope has led to major difficulties in the classical halo model, while a number of recent works have attempted to solve the problems by redefining the halo with new boundaries.
In this talk I will report our recent development of the depletion radius, which is a highly competitive new halo boundary stemming from the macroscopic physics of halo growth. I will show that the depletion radius is both an important physical probe for halo evolution and a concise geometric boundary for halo models of the large scale structure, capable of overcoming major limitations of the classical halo in a systematic way. I will also present our observational measurements of the depletion radius for both our Milky Way halo and DESI galaxy groups.
