The physical nature of the cosmic accretion of baryons and dark matter into halos and their galaxies

Understand

The cosmic accretion of both dark matter and baryons into halos typically is measured using some evolving virial relation, but recent work suggests that most halo growth at late cosmic time (z < 2) is not physical but is rather the by-product of an evolving virial radius (&#34;pseudo-evolution&#34;).

• Using Omega25, a suite of cosmological simulations that incorporate both dark matter and gas dynamics with differing treatments of gas cooling, star formation, and thermal feedback, we systematically explore the physics that governs cosmic accretion into halos and their galaxies.
• Physically meaningful cosmic accretion of both dark matter and baryons occurs at z > 1 across our halo mass range: M_200m = 10^{11-14} M_sun.
• However, dark matter, because it is dissipationless, is deposited (in a time-average sense) at > R_200m(z) in a shell-like manner, such that dark-matter mass and density experience little-to-no physical growth at any radius within a halo at z < 1.