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

## TL;DR

This paper investigates how ultra-light axion dark matter could form stable cores mimicking black holes, using core-halo relations and galactic observations to constrain axion mass, ruling out masses above 10^{-18} eV.

## Contribution

It provides new constraints on axion mass based on core-halo relations and galactic nucleus observations, linking dark matter properties to supermassive black hole mimickers.

## Key findings

- Axion masses greater than 10^{-18} eV are ruled out by galactic nucleus data.
- Solitonic core-halo relations can be used to constrain dark matter particle properties.
- Observations on sub-10 pc scales are crucial for these constraints.

## Abstract

If the dark matter is made of ultra-light axions, stable solitonic cores form at the centers of virialized halos. 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 $m < 10^{-18}$ eV is ruled out by the data. We briefly discuss whether an attractive self-interaction among axions could alleviate this constraint.