AxioNyx: Simulating Mixed Fuzzy and Cold Dark Matter

TL;DR

This paper introduces AxioNyx, a simulation framework combining fuzzy and cold dark matter dynamics to study their non-linear effects on galactic scales, including soliton formation and density profiles.

Contribution

It presents the first mixed fuzzy and cold dark matter simulations using an extended Nyx code with adaptive refinement and Schrödinger-Poisson dynamics.

Findings

Soliton formation depends on fuzzy dark matter fraction, occurring only above 10%.

Effective granule masses decrease proportionally with fuzzy dark matter fraction.

Fuzzy dark matter suppresses soliton growth quadratically.

Abstract

The distinctive effects of fuzzy dark matter are most visible at non-linear galactic scales. We present the first simulations of mixed fuzzy and cold dark matter, obtained with an extended version of the Nyx code. Fuzzy (or ultralight, or axion-like) dark matter dynamics are governed by the comoving Schr\"odinger-Poisson equation. This is evolved with a pseudospectral algorithm on the root grid, and with finite differencing at up to six levels of adaptive refinement. Cold dark matter is evolved with the existing N-body implementation in Nyx. We present the first investigations of spherical collapse in mixed dark matter models, focusing on radial density profiles, velocity spectra and soliton formation in collapsed halos. We find that the effective granule masses decrease in proportion to the fraction of fuzzy dark matter which quadratically suppresses soliton growth, and that a central soliton only forms if the fuzzy dark matter fraction is greater than 10\%. The Nyx framework supports baryonic physics and key astrophysical processes such as star formation. Consequently, AxioNyx will enable increasingly realistic studies of fuzzy dark matter astrophysics.