Structure-wide dark matter density depletion induced by local degeneracies

Abstract

The longstanding cusp-core problem--the discrepancy between the steep central density cusps predicted by cold dark matter (DM) simulations and certain shallow cores observed in dwarf galaxies, in particular the associated diversity of inner profiles--remains hotly debated despite decades of study. Building on a new interpretation of fermionic isothermal halos, we identify a physical mechanism--degeneracy-induced depletion--in which degenerate inner cores of fermionic DM suppress the surrounding density over large scales. This effect persists even in dense baryonic environments. Within the framework of hierarchical structure formation, degeneracies developed in the smallest constituent subhalos induce low-density regions that collectively configure into a King-type core of the host DM halo, with a core density-radius relation consistent with observations. This scenario accounts for the diversity of DM inner profiles through variation in the average degeneracy of constituent subhalos, and suggests a connection between this diversity and the halo formation history. Thus, the cusp-core problem may be reconciled within the standard "cold" DM paradigm without invoking strong baryonic feedback, instead pointing to the fermionic nature of DM.

Accepted for publication in ApJ

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