![]() ![]() I am currently interested to investigate the properties of dark matter haloes, how they form, what is their galaxy and dark-subhalo content and how they acquire a certain concentration. Small systems collapse first and then merge together forming larger ones: in this hierarchical pyramid, galaxy clusters represent the most bound structures in the Universe. When a dark matter density fluctuation exceeds the virial value predicted for collapse, it gives origin to a dark matter halo. The standard scenario of structure formation predicts that the formation of cosmic structures, up to proto-galactic scales, is gravitationally driven by dark matter. ![]() Only a small fraction of the total density is attributed to the baryonic component, which mainly constitutes hot and cold intergalactic gas, stars and planets. These results can be useful in semi-analytical models of galaxy formations, and also in the interpretation of substructure in either galaxies or galaxy clusters.Ĭurrent observational campaigns, designed to study the content of the Universe, have revealed that a large quantity of its content is made up of dark matter and dark energy. Independent on the subhalo-to-host mass ratio instead, it depends on cosmic time: at higher redshifts, when the universe is denser, mass loss per unit time is higher. I also estimated the subhalo mass-loss rate, and found that the fraction of mass lost per unit time is After satellites enter the host halo, I computed their self-bound mass and followed them snapshot by snapshot until the present day. those halos accreted by the main branch of the merger tree. I followed the merging history of the host halos and evaluated the distribution of satellites, i.e. I used the outputs of the two GIF N-Body simulations, and of a sample of re-simulated galaxy clusters, also to study the subhalo population of present-day dark matter halos. Extrapolating this mass function down to the neutralino Jeans mass (10 -6 M sun), I estimated the present day gamma-ray emission from microhalos populating a Milky Way-size halo (10 12 M sun/h) and computed their detectability using actual Cherenkov telescopes – GLAST-like satellite (Giocoli, Pieri and Tormen 2007). By integrating over redshift the conditional mass function, both the spherical and ellipsoidal model, I estimated the present-day population of dark matter subhalos, assuming no tidal stripping or merging among them. The conditional (progenitor) mass function, f(m,z|M 0,z 0)dm, describes the mass distribution at redshift z of dark matter halos that will end up in a system of mass M 0 at redshift z 0. I show (Giocoli, Moreno, Sheth and Tormen 2007) that a more accurate estimator can be obtained using the ellipsoidal collapse model (Sheth, Mo and Tormen 2001 Sheth and Tormen 2002). I found that – using the Lacey and Cole (1993) formation redshift distribution – the formation time is underestimated. The formation time is defined as the redshift at which the mass of the main progenitor becomes, for the first time, larger than half of the final halo mass. Starting from the present day I followed the history of the haloes backwards in time estimating their formation time distribution. The outputs of two cosmological N-Body simulations, GIF and GIF2, have been used to study the growth of dark matter halos. ![]() In it, I studied the formation of dark matter haloes, from primordial density perturbations, and their evolution along cosmic time. ![]() In 2008 I finished my PhD and the title of my dissertation was “Hierarchical Clustering: Structure Formations in the Universe”. ![]()
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