We present the full sample of measurements of the warm dust emission of 31 strongly-lensed, multiply imaged quasars, observed with JWST MIRI multiband imaging, which we use to constrain the particle properties of dark matter. The strongly lensed warm dust region of quasars is compact and statistically sensitive to a population of dark matter halos down to masses of ${10}^6{M}_{\odot }$. The high spatial resolution and infrared sensitivity of MIRI make it uniquely suited to measure multiply imaged warm dust emission from quasars and thus to infer the properties of low-mass dark halos. In this work, we present image fluxes as well as dark matter sensitive warm dust flux ratios inferred from spectral energy distribution fitting. We then use these flux ratios to test for the presence of a warm dark matter turnover in the halo mass function. We use a forward modeling pipeline which explores dark matter parameters while also accounting for tidal stripping effects on subhalos, globular clusters, and complex deflector macromodels with $m=1,m=3$, and $m=4$ elliptical multipole moments. Adopting a comparable prior on the projected density of substructure to previous analyses, the data presented here provide a factor of 2 improvement in sensitivity to a turnover in the halo mass function. Assuming subhalo abundance predicted by the semianalytic model galacticus, we infer with a Bayes factor of $10:1$, a half-mode mass $m_{\mathrm{hm}}<{10}^{7.8}{M}_{\odot }$. If instead we use a prior from $N$-body simulations, we infer $m_{\mathrm{hm}}<{10}^{7.6}{M}_{\odot }$. This corresponds to a thermally produced dark matter mass of 5.6 (6.4) keV for the galacticus and $N$-body priors, respectively. This is one of the strongest constraints to date on a turnover on the halo mass function, and the flux ratios and inference methodology presented here can be used to test a broad range of dark matter physics.

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• Dark matter
• Gravitational lenses
• Particle dark matter
• Galactic nuclei & quasars