Line of research overview

The Nature of the Dark Matter from the structural properties of Galaxies and Clusters

Principal Investigator: Paolo Salucci

Abstract: The distribution of the dark matter, in galaxies of different luminosity and Hubble type, has revealed itself to be much more than the evidence that dark particles govern the virialized structures of the Universe. In fact, it is clearly emerging the existence of a well-ordered and amazing scenario in which the structural properties of the dark matter halos are found to be in strong relationships with the corresponding ones of the baryonic components that they host (1). Although the available observations, over many aspects, are still partial, several unexpected correlations between the dark and the luminous sector have already been discovered (2). It appears that the mystery of the dark matter phenomenon has to be addressed by means of a reverse-engineering approach. According to this change of paradigm, the evident dark and luminous entanglement, detected in the structural properties of galaxies, carries crucial information about the unknown nature of the dark matter. This paradigm is clearly beyond the current one, according to which, the nature of DM is considered as known from first principles, while observations and experiments have the role of a final verification/falsification of the assumed scenario for dark matter The observational results obtained by different groups and also planned to be discussed /elaborated at IFPU are thought to strengthen the need of the above paradigm shift. (3) Moreover, this new approach can open the way to the currently little favoured scenario in which the dark particle interacts, over cosmological times, with Standard Model Particles.

Status of project and perspectives: The project is set to obtain/investigate a) the inner kinematics of galaxies so as b) the weak/strong lensing signals around them and 3) any other tracer of their gravitational fields. This strategy set to determine the nature of Dark matter is also suggested by the fact that the WIMP, the currently preferred particle coming from first principles, fails in being the constituent dark particle in galaxies. (4) The aim of this project is to extract, from the above descibed data, the values of the galaxy dark/luminous mass fraction, the halos central densities and lenght-scales that will serve as a crucial step towards the Nature of the dark particle. Such results from observations concerning the dark particle will be used as pillars of appropriate N-Body hydro-dynamical simulations set up to describe the cosmological history of galaxies (5). This investigation will be carried out for the whole mass scale of virialized objects i.e. , also in clusters and groups of galaxies. Clusters of galaxies are natural tools to unveil important aspects of the cosmological evolution of Dark matter, once we resort to high quality simulations. (6) In particular, merging of Galaxy Clusters, one of the most energetic event in the Universe can be used to probe the nature of DM in a way which is alternative to that we use in galaxies.(7) The IFPU offers an unique opportunity for scientists in different observational projects on dark matter in galaxies and clusters so as those in cosmo numerical simulation groups, in Elementary particles theory and experimentalists to gather together in a single place and try to get the whole picture of the Dark matter in the Universe. This will be done also by hosting dedicated meetings, scientific visits, and workshops. The team of proposers will host brainstormings and meetings on a monthly basis at the IFPU, spending at the institute from 1 to 2 days per week, as well as organizing regular seminars at the site. Moreover, the team will propose a living program of visits, dedicated and focussed meetings, and workshops throughout the academic year. We also like to organize for the subject of Dark Matter in Galaxies a medium size summer school every two years. All activities are meant to attract also members from all the founding institutions. References (1) Salucci, P. Lapi, A. Tonini, C. et al 2007, MNRAS, 378, 41 Karukes E.~V., Salucci P., 2017, MNRAS, 465, 4703 Persic, M. Salucci, P. Stel, F. 1996, MNRAS, 281, 27 (2) Gentile, G; Famaey, B., Zhao, H.; Salucci, P. 2009. Nature, 461, 627 (3) Salucci ,P. 2019, The Astronomy and Astrophysics Review\” 27,2 (4) Bullock JS, Boylan-Kolchin M (2017) ARAA 55:343 (5) Chua K.~T.~E., Pillepich A., Vogelsberger M., Hernquist L., 2019, MNRAS, 484, 476 (6)Biffi V., Sembolini F., De Petris M., Valdarnini R et al , 2014, MNRAS, 439, 588