Gravitational lensing by wave dark matter halos

TL;DR

This paper investigates whether wave dark matter halos can produce strong gravitational lensing effects, analyzing different density profiles and their compatibility with observed lensing systems to constrain the properties of wave dark matter.

Contribution

It provides an analytical and numerical analysis of wave dark matter halo profiles, especially soliton and NFW combinations, to determine their lensing capabilities and parameter constraints.

Findings

Pure soliton profiles produce weaker lensing than other cored profiles.

NFW envelope around the soliton is necessary to match observed Einstein radii.

Lower bound on boson mass is established at m_a > 10^{-24} eV.

Abstract

Wave Dark Matter (WaveDM) has recently gained attention as a viable candidate to account for the dark matter content of the Universe. In this paper we explore the extent to which dark matter halos in this model, and under what conditions, are able to reproduce strong lensing systems. First, we analytically explore the lensing properties of the model -- finding that a pure WaveDM density profile, a soliton profile, produces a weaker lensing effect than other similar cored profiles. Then we analyze models with a soliton embedded in an NFW profile, as has been found in numerical simulations of structure formation. We use a benchmark model with a boson mass of $m_a=10^{-22}{\rm eV}$, for which we see that there is a bi-modality in the contribution of the external NFW part of the profile, and actually some of the free parameters associated with it are not well constrained. We find that for configurations with boson masses $10^{-23}$ -- $10^{-22}{\rm eV}$, a range of masses preferred by dwarf galaxy kinematics, the soliton profile alone can fit the data but its size is incompatible with the luminous extent of the lens galaxies. Likewise, boson masses of the order of $10^{-21}{\rm eV}$, which would be consistent with Lyman-$\alpha$ constraints and consist of more compact soliton configurations, necessarily require the NFW part in order to reproduce the observed Einstein radii. We then conclude that lens systems impose a conservative lower bound $m_a > 10^{-24}$ and that the NFW envelope around the soliton must be present to satisfy the observational requirements.