Cosmological puzzle resolved by stellar feedback in high redshift galaxies

TL;DR

This paper demonstrates through simulations that stellar feedback-driven gas motions in early galaxies can flatten dark matter cusps, resolving a key discrepancy between observations and cosmological predictions on galactic scales.

Contribution

The study introduces a novel mechanism showing that gas motions driven by supernova feedback can flatten dark matter cusps in early galaxies, explaining observed core profiles.

Findings

Gas motions from supernova feedback flatten dark matter cusps.

Flattened cores are preserved during galaxy mergers.

The mechanism operates in all star-forming galaxies at high redshift.

Abstract

The standard cosmological model, now strongly constrained by direct observation at early epochs, is very successful in describing the structure of the evolved universe on large and intermediate scales. Unfortunately, serious contradictions remain on smaller, galactic scales. Among the major small-scale problems is a significant and persistent discrepancy between observations of nearby galaxies, which imply that galactic dark matter (DM) haloes have a density profile with a flat core, and the cosmological model, which predicts that the haloes should have divergent density (a cusp) at the centre. Here we use numerical N-body simulations to show that random bulk motions of gas in small primordial galaxies, of the magnitude expected in these systems, result in a flattening of the central DM cusp on short timescales (of order 10^8 years). Gas bulk motions in early galaxies are driven by supernova explosions which result from ongoing star formation. Our mechanism is general and would have operated in all star-forming galaxies at redshifts z>~ 10. Once removed, the cusp cannot be reintroduced during the subsequent mergers involved in the build-up of larger galaxies. As a consequence, in the present universe both small and large galaxies would have flat DM core density profiles, in agreement with observations.