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ABSTRACT The free-streaming length of dark matter depends on fundamental dark matter physics, and determines the abundance and concentration of dark matter haloes on sub-galactic scales. Using the image positions and flux ratios from eight quadruply imaged quasars, we constrain the free-streaming length of dark matter and the amplitude of the subhalo mass function (SHMF). We model both main deflector subhaloes and haloes along the line of sight, and account for warm dark matter free-streaming effects on the mass function and mass–concentration relation. By calibrating the scaling of the SHMF with host halo mass and redshift using a suite of simulated haloes, we infer a global normalization for the SHMF. We account for finite-size background sources, and marginalize over the mass profile of the main deflector. Parametrizing dark matter free-streaming through the half-mode mass mhm, we constrain the thermal relic particle mass mDM corresponding to mhm. At $$95 \, {\rm per\, cent}$$ CI: mhm < 107.8 M⊙ ($$m_{\rm {DM}} \gt 5.2 \ \rm {keV}$$). We disfavour $$m_{\rm {DM}} = 4.0 \,\rm {keV}$$ and $$m_{\rm {DM}} = 3.0 \,\rm {keV}$$ with likelihood ratios of 7:1 and 30:1, respectively, relative to the peak of the posterior distribution. Assuming cold dark matter, we constrain the projected mass in substructure between 106 and 109 M⊙ near lensed images. At $$68 \, {\rm per\, cent}$$ CI, we infer $$2.0{-}6.1 \times 10^{7}\, {{\rm M}_{\odot }}\,\rm {kpc^{-2}}$$, corresponding to mean projected mass fraction $$\bar{f}_{\rm {sub}} = 0.035_{-0.017}^{+0.021}$$. At $$95 \, {\rm per\, cent}$$ CI, we obtain a lower bound on the projected mass of $$0.6 \times 10^{7} \,{{\rm M}_{\odot }}\,\rm {kpc^{-2}}$$, corresponding to $$\bar{f}_{\rm {sub}} \gt 0.005$$. These results agree with the predictions of cold dark matter.
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Mixed warm dark matter constraints using Milky Way satellite galaxy counts
Warm dark matter has been strongly constrained in recent years as the sole component of dark matter. However, a less-explored alternative is that dark matter consists of a mixture of warm and cold dark matter (MWDM). In this work, we use observations of Milky Way satellite galaxies to constrain MWDM scenarios where the formation of small-scale structure is suppressed either by generic thermal relic warm dark matter or a sterile neutrino produced through the Shi-Fuller mechanism. To achieve this, we model satellite galaxies by combining numerical simulations with semianalytical models for the subhalo population, and use a galaxy-halo connection model to match galaxies onto dark matter subhalos. By comparing the number of satellites predicted by MWDM models to the observed satellite population from the Dark Energy Survey and Pan-STARRS1, we constrain the fraction of warm dark matter, 𝑓WDM, as a function of its mass, 𝑚WDM. We exclude dark matter being composed entirely of thermal relic warm dark matter with 𝑚WDM ≤6.6 keV at a posterior ratio of 10∶1, consistent with previous works. However, we find that warm dark matter with smaller mass is allowed when mixed with cold dark matter, and that the 𝑓WDM constraints strengthen with decreasing 𝑚WDM until they plateau at 𝑓WDM ≲0.45 for 𝑚WDM ≲1.5 keV. Likewise, in the case of a sterile neutrino with mass of 7 keV produced through the Shi-Fuller mechanism, we exclude a fraction of 𝑓𝜈𝑠 ≲0.45, independent of mixing angle. Our results extend constraints on MWDM to a region of parameter space that has been relatively unconstrained with previous analysis.
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- Award ID(s):
- 2307126
- PAR ID:
- 10636872
- Publisher / Repository:
- Physical Review Journals
- Date Published:
- Journal Name:
- Physical Review D
- Volume:
- 111
- Issue:
- 6
- ISSN:
- 2470-0010
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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