Abstract
Evidence for dark matter (DM) was originally discovered in 1933 by Zwicky (Zwicky 1933, 1937), and has defied all explanations since then. The original discovery was based on the motions of galaxies in clusters of galaxies. The MicroWave Back Ground (MWBG) observations by the Planck mission and other satellites give definitive numbers. Galaxy correlations give results down to small galaxies, which match theoretical expectations. Here we focus on a few interesting aspects, that may allow to determine the nature of dark matter: (1) Ultra Faint Dwarf (UFD) galaxies, that represent the oldest galaxies known. UFDs are almost devoid of baryonic matter. (2) Calculations show that there can be super-sonic flow of baryonic matter. It follows that there are ubiquitous shockwaves; commonly oblique they generate vorticity. (3) Early virialized clumps, mini-halos, have a density that is consistent with the density implied by Super Massive Black Holes (SMBHs) today, if we assume that SMBHs grow by merging, akin to the Press & Schechter (1974) picture for galaxies. This implies that the oldest SMBHs observed today give powerful constraints on the very early phases.
Highlights
Dark matter (DM) has been with us since Zwicky noted its presence in clusters of galaxies [1,2]
(3) Early virialized clumps, mini-halos, have a density that is consistent with the density implied by Super Massive Black Holes (SMBHs) today, if we assume that SMBHs grow by merging, akin to the Press & Schechter (1974) picture for galaxies
The question we explore here is whether the process from virialization of a mini-halo to a dwarf galaxy or SMBH is helped along by Warm Dark Matter (WDM), because WDM can start a run-away cooling and star formation already at high redshift [62]
Summary
Dark matter (DM) has been with us since Zwicky noted its presence in clusters of galaxies [1,2]. Its density ρDM in galaxies follows to a fair approximation the isothermal gas sphere law by Emden [14] of ρDM ∼ r−2 for large distances, where r is the radial distance This gives immediately the flat rotation curves observed, showing that DM reaches out far further than the baryonic matter, that is traced by hot and cold gas, stars, while both kinds of matter are shown by gravitational lensing. For any proposed WDM model it needs to be shown that it can reproduce both the MWBG fluctuations, as well as the smaller scale observations available, as was done by the Planck-collaboration [15] Such a model has to show how it can allow to interpret the Gaia data. De Propris et al [7] noted that even DM may not be in equilibrium yet around clusters of galaxies
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