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Register a new userSimulating the hidden giant in cold and self-interacting dark matter models
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We perform a series of controlled N-body simulations to study realizations of the recently discovered Antlia 2 galaxy in cold dark matter (CDM) and self-interacting dark matter (SIDM) scenarios. Our simulations contain six benchmark models, where we vary the initial halo concentration and the self-scattering cross section. We adopt well-motivated initial stellar and halo masses, and our fiducial orbit has a small pericenter. After evolving in the Milky Ways tidal field, the simulated galaxies experience significant mass loss and their stellar distributions expand accordingly. These tidal effects are more prominent if the initial halo concentration is lower and if the self-scattering cross section is larger. Our results show that Antlia 2-like galaxies could be realized in CDM if the halo concentration is low and the stellar distribution is diffuse at the infall time, while these conditions could be relaxed in SIDM. We also find all the simulated galaxies predict approximately the same stellar velocity dispersion after imposing selection criteria for stellar particles. This has important implications for testing dark matter models using tidally disturbed systems.
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The nature of the dark matter can affect the collapse time of dark matter haloes, and can therefore be imprinted in observables such as the stellar population ages and star formation histories of dwarf galaxies. In this paper we use high resolution hydrodynamical simulations of Local Group-analogue (LG) volumes in cold dark matter (CDM), sterile neutrino warm dark matter (WDM) and self-interacting dark matter (SIDM) models with the EAGLE galaxy formation code to study how galaxy formation times change with dark matter model. We are able to identify the same haloes in different simulations, since they share the same initial density field phases. We find that the stellar mass of galaxies depends systematically on resolution, and can differ by as much as a factor of two in haloes of a given dark matter mass. The evolution of the stellar populations in SIDM is largely identical to that of CDM, but in WDM early star formation is instead suppressed. The time at which LG haloes can begin to form stars through atomic cooling is delayed by $sim$200~Myr in WDM models compared to CDM. It will be necessary to measure stellar ages of old populations to a precision of better than 100~Myr, and to address degeneracies with the redshift of reionization -- and potentially other baryonic processes -- in order to use these observables to distinguish between dark matter models.
Recently, Meneghetti et al. reported an excess of small-scale gravitational lenses in galaxy clusters, compared to simulations of standard cold dark matter (CDM). We propose a self-interacting dark matter (SIDM) scenario, where a population of subhalos in the clusters experiences gravothermal collapse. Using controlled N-body simulations, we show the presence of early-type galaxies in substructures accelerates gravothermal evolution and a collapsed SIDM subhalo has a steeper density profile than its CDM counterpart, leading to a larger radial galaxy-galaxy strong lensing cross section and more lens images, in better agreement with the observations. Our results indicate that strong gravitational lensing can provide a promising test of the self-interacting nature of dark matter.
We show that hidden hot dark matter, hidden-sector dark matter with interactions that decouple when it is relativistic, is a viable dark matter candidate provided it has never been in thermal equilibrium with the particles of the standard model. This hidden hot dark matter may reheat to a lower temperature and number density than the visible Universe and thus account, simply with its thermal abundance, for all the dark matter in the Universe while evading the typical constraints on hot dark matter arising from structure formation. We find masses ranging from ~3 keV to ~10 TeV. While never in equilibrium with the standard model, this class of models may have unique observational signatures in the matter power spectrum or via extra-weak interactions with standard model particles.
We use a semianalytic approach that is calibrated to N-body simulations to study the evolution of self-interacting dark matter cores in galaxies. We demarcate the regime where the temporal evolution of the core density follows a well-defined track set by the initial halo parameters and the cross section. Along this track, the central density reaches a minimum value set by the initial halo density. Further evolution leads to an outward heat transfer, inducing gravothermal core collapse such that the core shrinks as its density increases. We show that the time scale for the core collapse is highly sensitive to the outer radial density profile. Satellite galaxies with significant mass loss due to tidal stripping should have larger central densities and significantly faster core collapse compared to isolated halos. Such a scenario could explain the dense and compact cores of dwarf galaxies in the Local Group like Tucana (isolated from the Milky Way), the classical Milky Way satellite Draco, and some of the ultrafaint satellites. If the ultimate fate of core collapse is black hole formation, then the accelerated time scale provides a new mechanism for creating intermediate mass black holes.
A thick dark matter disk is predicted in cold dark matter simulations as the outcome of the interaction between accreted satellites and the stellar disk in Milky Way sized halos. We study the effects of a self-interacting thick dark disk on the energetic neutrino flux from the Sun. We find that for particle masses between 100 GeV and 1 TeV and dark matter annihilation to heavy leptons either the self-interaction may not be strong enough to solve the small scale structure motivation or a dark disk cannot be present in the Milky Way.
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