New Model of Density Distribution for Fermionic Dark Matter Halos

Abstract

PACSIn this paper, we formulate a new model of density distribution for halos made of warm dark matter (WDM) particles. The model is described by a single microphysics parameter the mass (or, equivalently, the maximal value of the initial phase-space density distribution) of dark matter particles. Given the WDM particle mass and the parameters of a dark matter density profile at the halo periphery, this model predicts the inner density profile. In case of initial Fermi-Dirac distribution, we successfully reproduce cored dark matter profiles from N -body simulations. Also, we calculate the core radii of warm dark matter halos of dwarf spheroidal galaxies for particle masses mfd = 100, 200, 300 and 400 eV. K e y w o r d s: Dark matter: warm, cold; dark matter halo profile; cores; Navarro-Frenk-White profileThe nature of dark matter the largest gravitating substance in the Universe is not yet identified. Usual (left-handed) neutrinos the only natural dark matter candidate within the Standard Model of particle physics are too light to form the observed large-scale structure of the Universe [1] and the densest dark matter-dominated objects, dwarf spheroidals (dSphs) [2]. So far, many extensions of the Standard Model containing a viable dark matter candidate have been proposed; see, e.g., reviews [3][4][5][6]. In terms of their initial velocities, valid dark matter candidates can be split in two groups 1 (see, e.g., [9]):• cold dark matter (CDM), composed of particles with small (non-relativistic) initial velocities [10,11]; c A.V. RUDAKOVSKYI, D.O. SAVCHENKO, 2018 1 Note that, for some specific dark matter particle candidates, their initial velocity spectrum can be approximated by a mixture of 'cold ' and 'warm' components [7, 8].• warm dark matter (WDM), composed of particles with large (relativistic) initial velocities [12,13].Density distribution of CDM haloes is often described by the Navarro-Frenk-White (NFW) profile [14,15] ρ nfw (r) = ρ s r s r 1 + r rs 2 . (1) Its parameters ρ s and r s are connected with the halo mass M 200 (the mass within the sphere of radius R 200 , within which the average density is 200 times larger than the critical density ρ crit of the Universe) and halo concentration parameter c 200 = R 200 /r s .The phase-space density for CDM haloes becomes infinite towards the halo centre; see, e.g., [16]. For WDM, this is not true: its maximal phase-space density f max is finite at early times and does not increase during halo formation [17]. Usually, density distri-

New mass bound on fermionic dark matter from a combined analysis of classical dSphs

“…We call the obtained profile tNFW (stands for truncated Navarro-Frenk-White) hereafter. The density profiles obtained in this model are in a good agreement with numerical N-body simulations (Shao et al 2013;Macciò et al 2013a,b), see more in Rudakovskyi & Savchenko (2018). Given the density distribution of a dark matter halo, we follow the logic of Domcke & Urbano (2015) and Di Paolo et al (2018) to obtain the velocity dispersion along the line of sight.…”

“…for the subsequent step. Rudakovskyi & Savchenko (2018) shows good convergence of this procedure after several iterations. We call the obtained profile tNFW (stands for truncated Navarro-Frenk-White) hereafter.…”

“…For a steady-state isotropic spherically symmetrical dark matter halo (see Rudakovskyi & Savchenko (2018) for a discussion on the applicability of this assumption) the phase space density f is obtained by using the Eddington transformation (Eddington 1916;Binney & Tremaine 2008) f…”

“…In return, it requires a (semi-)analytical model of the DM density profile and stellar density profile. Many analytical models of fermionic DM halo density profiles have been developed so far; see, e.g., Ruffini & Stella (1983); Bilić & Viollier (1997) Randall et al (2017); Rudakovskyi & Savchenko (2018); Giraud & Peschanski (2018); Barranco et al (2018).…”

“…In this paper, we present a new lower bound on the mass of fermionic DM particle, based on the observed kinematics (Bonnivard et al 2015) and photometry (McConnachie 2012) data of 'classical' dSphs, and assuming the DM density model of Rudakovskyi & Savchenko (2018). In comparison to Domcke & Urbano (2015), Di Paolo et al (2018), this approach allows us not only to analyse individual dSphs, but also to perform combined statistical analysis based on the total χ 2 goodness-of-fit statistics assuming the same dark matter particle mass in all of them.…”