Question

What is meant by “shallow density profile” in the context of dark matter halos?

Answer 1

The cuspy halo problem (also known as the core-cusp problem) refers to a discrepancy between the inferred dark matter density profiles of low-mass galaxies and the density profiles predicted by cosmological N-body simulations. Nearly all simulations form dark matter halos which have "cuspy" dark matter distributions, with density increasing steeply at small radii, while the rotation curves of most observed dwarf galaxies suggest that they have flat central dark matter density profiles ("cores").[1][2]

Several possible solutions to the core-cusp problem have been proposed. Many recent studies have shown that including baryonicfeedback (particularly feedback from supernovae and active galactic nuclei) can "flatten out" the core of a galaxy's dark matter profile, since feedback-driven gas outflows produce a time-varying gravitational potentialthat transfers energy to the orbits of the collisionless dark matter particles.[3][4] Other works have shown that the core-cusp problem can be solved outside of the most widely accepted Cold Dark Matter (CDM) paradigm: simulations with warm or self-interacting dark matter also produce dark matter cores in low-mass galaxies.[5][6]

Answer 2

Explanation:

I provide notes on the NFW, Einasto, Sersic, and other mass profiles which provide good fits to simulated dark matter halos (S3).