Axion core–halo mass and the black hole–halo mass relation: constraints on a few parsec scales

Abstract

ABSTRACT If the dark matter is made of ultralight axions, stable solitonic cores form at the centres of virialized haloes. In some range for the mass m of the axion particle, these cores are sufficiently compact and can mimic supermassive black holes (SMBH) residing at galactic nuclei. We use the solitonic core–halo mass relation, validated in numerical simulations, to constrain a new range of allowed axion mass from measurements of the SMBH mass in (pseudo)bulge and bulgeless galaxies. These limits are based on observations of galactic nuclei on scales smaller than 10 pc. Our analysis suggests that $m\lesssim 10^{-18}\, {\rm eV}$ is ruled out by the data. We briefly discuss whether an attractive self-interaction among axions could alleviate this constraint.