Dark Matter Substructure: A Lensing Perspective

TL;DR

This paper investigates dark matter substructure using strong gravitational lensing, employing semi-analytic models to predict subhalo properties and assess the impact of a central galaxy on subhalo density near Einstein radii.

Contribution

It provides a comprehensive suite of semi-analytic galaxy formation models to study subhalo distributions relevant for lensing, including effects of a central galaxy, across various halo masses and redshifts.

Findings

Models agree with N-body simulations within a factor of 2 near Einstein radius.

Adding a central galaxy reduces subhalo density by about 15%.

Subhalo properties vary with host mass and redshift, informing dark matter physics.

Abstract

The study of dark matter substructure through strong gravitational lensing has shown enormous promise in probing the properties of dark matter on sub-galactic scales. This approach has already been used to place strong constraints on a wide range of dark matter models including self-interacting dark matter, fuzzy dark matter and warm dark matter. A major source of degeneracy exists between suppression of low mass halos due to novel dark matter physics and the strength of tidal stripping experienced by subhalos. We study theoretical predictions for the statistical properties of subhalos in strong gravitational lenses using the semi-analytic galaxy formation toolkit: galacticus. We present a large suite of dark matter only galacticus models, spanning nearly two orders of magnitude in host halo mass (from Milky Way to group mass halos between redshifts from $0.2$ to $0.8$). Additionally, we include a smaller set of galacticus runs with the potential of a central massive elliptical to complement our dark matter only suite of models. We place particular focus on quantities relevant to strong gravitational lensing; namely the projected number density of substructure near the Einstein radius as function of host stellar mass and redshift. In the innermost region in projection, we find that our galacticus models agrees with N-body simulations within a factor of $\sim 2$ within the Einstein radius. We find that the addition of a central galaxy suppresses the projected number density of subhalos within in the Einstein radius by around $15\%$ relative to dark matter only simulations.