Large fluctuations and cusp-core transformation in dwarf galaxies

Abstract

Dwarf galaxies are abundant and dark matter dominated, rendering them particularly relevant for testing a cosmological model dominated by a dark sector. Whether their density profiles agree with $\Lambda$CDM expectations has long been a point of contention, dubbed the cusp/core problem. While numerical simulations have suggested that the erasure of central dark matter cusps may arise from potential fluctuations in feedback-driven gas, whether the required fluctuation levels are achieved in actual galaxies has remained uncertain. By measuring the power spectra of neutral gas density contrasts in a sample of gas-rich dwarf galaxies, we show that the observed fluctuations match theoretical expectations when their impact is derived from a stochastic dynamical model. Specifically, the relaxation times for core formation at the observationally estimated radii are generally on the order of a Hubble time or less. Core sizes are therefore consistent with conservative estimates assuming their generation through steady fluctuations acting over cosmic history. The relaxation time increases with halo mass, suggesting that core formation via this mechanism becomes less efficient in more massive systems.