Exploring Dark Matter’s Nature from Local Galactic Dynamics to High-z JWST Observations

The Cold Dark Matter paradigm emerged as the prevailing solution to the cosmic missing mass conundrum. While highly successful on cosmological scales, this model is partially inconsistent with galaxy-scale observations. This thesis addresses such a challenge by pursuing a dual approach. The first part presents a model featuring a dynamical non-minimal dark matter-gravity coupling originally developed in Bettoni et al. (2014). Such an effect is theoretically motivated and could solve some of the long-standing galaxy-scale issues of the Cold Dark Matter paradigm exploiting a single free parameter: the non-minimal coupling lengthscale. To begin with, I will study the self-gravitating equilibria of the dark matter halo predicted by this framework. Remarkably, the non-minimal coupling can produce cored dark matter halo profiles, similar in shape to the phenomenological Burkert model. Moreover, the predicted profiles are consistent with the core-surface density relation observed for dwarf galaxies. A Bayesian analysis will then test the non-minimally coupled dark matter model against stacked rotation curves of a broad sample of spiral galaxies. In terms of reduced chi-squared, the fits yielded by this model are always superior to the standard, Cold Dark Matter Navarro–Frenk–White profile and always competitive with the phenomenological Burkert profile. On the other hand, I will show how this model can explain the observed interplay between dark matter and baryons in late-type galaxies, embodied by tight dynamical scaling relations such as the Radial Acceleration Relation. The analysis predicts a power-law relationship between the non-minimal coupling lengthscale and the virial mass of dark matter haloes. After using the non-minimally coupled dark matter model to fit galaxy clusters’ pressure profiles from the X-COP collaboration, I will show that such scaling holds consistently from the dwarf-galaxy regime up to galaxy clusters’ virial masses. Overall, this single-parameter simple model shows a rich phenomenology in a comprehensive set of scales capable of addressing long-standing issues of the Cold Dark Matter paradigm. In the second part of the thesis, I will discuss how high-redshift observations from new, high-resolution instruments such as the James Webb Space Telescope can significantly enhance our knowledge about dark matter. Specifically, I will present a new technique to constrain dark matter astroparticle properties that relies on JWST’s cutting-edge high-redshift observations of the cosmic star formation rate density. The forecasts obtained with this technique demonstrate how upcoming ultra-faint galaxy surveys in the (pre) reionization era will be determinant to probe the microscopic nature of the elusive dark matter particles, potentially ruling out alternative dark matter models to the pure Cold Dark Matte framework. In summary, the apparatus created within this thesis introduces novel techniques that have the potential to play a crucial role in the evaluation of both established and future models concerning dark matter or modified gravity theories. On the one hand, the analysis framework developed for assessing the characteristics of the non-minimally coupled dark matter model can be adapted for scrutinizing other alternative dark matter scenarios or modified gravity theories, including the ongoing investigation of the Fractional Gravity framework. On the other hand, the extensive observations conducted by JWST will extend further into the high-redshift Universe, rendering the methodologies outlined in this thesis exceptionally valuable in generating new and competitive constraints on the nature of dark matter.