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We model the total mass and galactic substructure in the strong lensing galaxy cluster MACS J0138.0-2155 using a combination of Chandra X-ray data, Multi-Unit Spectroscopic Explorer (MUSE) spectroscopy, and Hubble Space Telescope imaging. MACS J0138.0-2155 lenses a source galaxy at z=1.95 which hosts two strongly lensed supernovae, Requiem and Encore. We find MACS J0138.0-2155 to have an X-ray temperature of 6.7 +/- 0.4 keV and a velocity dispersion of cluster member galaxies of 718^{+132}_{-182} km/s, which indicate a cluster mass of ~5 x 10^{14} solar masses. The round morphology of the X-ray emission indicates that this cluster is relaxed with an ellipticity within the lensing region of e=0.12 +/- 0.03. Using 18 of the brightest, non-blended, quiescent galaxies, we fit the cluster specific Faber-Jackson relation, including a set of 81 variations in the analysis choices to estimate the systematic uncertainties in our results. We find a slope of alpha = 0.26 +/- 0.06 (stat.) +/- 0.03 (sys.) with an intrinsic scatter of 31^{+8}_{-6} (stat.) +/- 4 (sys.) km/s at a reference velocity dispersion of ~220 km/s. We also report on significant galaxies along the line-of-sight potentially impacting the lens modeling, including a massive galaxy with stellar velocity dispersion of 291 +/- 3 km/s$ which lies close in projection to the central cluster galaxy. This galaxy is part of a small group at a slightly higher redshift than the cluster., Comment: submitted to Open Journal of Astrophysics

Evidence for high-redshift supermassive black holes challenges standard scenarios for how such objects form in the early universe. Here, we entertain the possibility that a fraction of the cosmological dark matter could be ultra-strongly self interacting. This would imply that gravothermal collapse occur at early times in the cores of dark matter halos, followed by accretion. We study under which conditions on the abundance and interaction strength and structure of such ultra self-interacting dark matter the black holes resulting from the end-point of gravothermal core collapse can seed the observed, early-forming supermassive black holes. We find, depending on the velocity dependence of the self-interaction cross section, a bimodal structure in the favored parameter space, where data points to either a small collapsing dark matter fraction with a large cross section, or a large fraction and a relatively small cross section. While self-interaction cross sections with different velocity dependence can explain observations, we find that the best, self-consistent results correspond to a Rutherford-like self-interaction, typical of long-range dark-sector forces with light mediators. We discuss complementary observational probes if this scenario is realized in nature, focusing especially on the expected intermediate mass black holes predicted to exist in smaller galaxies., Comment: 28 pages, 6 Figures

The rotation curves of spiral galaxies exhibit a great diversity that challenge our understanding of galaxy formation and the nature of dark matter. Previous studies showed that in self-interacting dark matter (SIDM) models with a cross section per unit mass of $\sigma/m\approx{\cal O}(1)~{\rm cm^2/g}$, the predicted dark matter central densities are a good match to the observed densities in galaxies. In this work, we explore a regime with a larger cross section of $\sigma/m\approx20-40~{\rm cm^2/g}$ in dwarf galactic halos. We will show that such strong dark matter self-interactions can further amplify the diversity of halo densities inherited from their assembly history. High concentration halos can enter the gravothermal collapse phase within $10~{\rm Gyr}$, resulting in a high density, while low concentration ones remain in the expansion phase and have a low density. We fit the rotation curves of $14$ representative low surface brightness galaxies and demonstrate how the large range of observed central densities are naturally accommodated in the strong SIDM regime of $\sigma/m\approx20-40~{\rm cm^2/g}$. Galaxies that are outliers in the previous studies due to their high halo central densities, are no longer outliers in this SIDM regime as their halos would be in the collapse phase. For galaxies with a low density, the SIDM fits are robust to the variation of the cross section. Our findings open up a new window for testing gravothermal collapse, the unique signature of strong dark matter self-interactions, and exploring broad SIDM model space., Comment: 21 pages, 14 figures

We study the impact on the trajectory of high-energy cosmic-ray protons of scattering off the cosmic dark matter. We compute the scattering angle as a function of the cosmic-ray energy, of the dark matter mass, and of the interaction strength for a few representative choices for the relevant interaction cross section. We find that the typical deflection angle over the cosmic ray path is largely independent of the dark matter mass. Given existing limits on the interaction strength, we compute the average deflection angle. We find that for large interaction cross sections and low cosmic ray energies, the predicted deflection angle is much larger than the angular resolution of very high-energy cosmic-ray observatories such as Pierre Auger., Comment: 26 pages, 9 Figures

We analyze strongly lensed images in 8 galaxy clusters to measure their dark matter density profiles in the radial region between 10 kpc and 150 kpc, and use this to constrain the self-interaction cross section of dark matter (DM) particles. We infer the mass profiles of the central DM halos, bright central galaxies, key member galaxies, and DM subhalos for the member galaxies for all 8 clusters using the Qlens code. The inferred DM halo surface densities are fit to a self-interacting dark matter (SIDM) model, which allows us to constrain the self-interaction cross section over mass $\sigma$/m. When our full method is applied to mock data generated from two clusters in the Illustris-TNG simulation, we find results consistent with no dark matter self-interactions as expected. For the eight observed clusters with average relative velocities of $1458_{-81}^{+80}$ km/s, we infer $\sigma$/m = $0.082_{-0.021}^{+0.027}$ cm$^2$/g and $\sigma$/m < 0.13 cm$^2$/g at the 95% confidence level., Comment: 28 pages