Constraints on the mass-concentration relation of cold dark matter halos with 11 strong gravitational lenses

TL;DR

This paper presents the first observational constraints on the mass-concentration relation of dark matter halos on sub-galactic scales using strong gravitational lensing data from eleven quads, providing new insights into dark matter structure formation.

Contribution

It introduces a novel method to measure the mass-concentration relation of dark matter halos at sub-galactic scales using strong lensing, accounting for subhalos and line of sight effects.

Findings

Measured halo concentrations at various masses, e.g., $c=12_{-5}^{+6}$ for $10^{8} M_{igodot}$ halos.

Results are consistent with theoretical predictions of the mass-concentration relation.

Demonstrated strong lensing as a powerful probe of dark matter halo properties on small scales.

Abstract

The mass-concentration relation of dark matter halos reflects the assembly history of objects in hierarchical structure formation scenarios, and depends on fundamental quantities in cosmology such as the slope of the primordial matter power-spectrum. This relation is unconstrained by observations on sub-galactic scales. We derive the first measurement of the mass-concentration relation using the image positions and flux ratios from eleven quadruple-image strong gravitational lenses (quads) in the mass range $10^{6} - 10^{10} M_{\odot}$, assuming cold dark matter. Our analysis framework includes both subhalos and line of sight halos, marginalizes over nuisance parameters describing the lens macromodel, accounts for finite source effects on lensing observables, and simultaneously constrains the normalization and logarithmic slope of the mass-concentration relation, and the normalization of the subhalo mass function. At $z=0$, we constrain the concentration of $10^{8} M_{\odot}$ halos $c=12_{-5}^{+6}$ at $68 \%$ CI, and $c=12_{-9}^{+15}$ at $95 \%$ CI. For a $10^{7} M_{\odot}$ halo, we obtain $68 \%$ ($95 \%$) constraints $c=15_{-8}^{+9}$ ($c=15_{-11}^{+18}$), while for $10^{9} M_{\odot}$ halos $c=10_{-4}^{+7}$ ($c=10_{-7}^{+14}$). These results are consistent with the theoretical predictions from mass-concentration relations in the literature, and establish strong lensing by galaxies as a powerful probe of halo concentrations on sub-galactic scales across cosmological distance.