Theoretical dark matter halo density profile

Abstract

We derive the density profile for collisionless dissipationless dark matter haloes in hierarchical cosmologies making use of the Secondary Infall (SI) model. The novelties are: i) we deal with triaxial virialised objects; ii) their seeds in the linear regime are peaks endowed with {\it unconvolved} spherically averaged density profiles according to the peak formalism; iii) the initial peculiar velocities are taken into account; and iv) accreting haloes are assumed to develop from the inside out, keeping the instantaneous inner system unaltered. The validity of this latter assumption is accurately checked by comparing analytical predictions on such a growth with the results of numerical simulation. We show that the spherically averaged density profile of virialised objects can be inferred with no need to specify their shape. The {\it typical} spherically averaged halo density profile is inferred, down to arbitrarily small radii, from the power-spectrum of density perturbations. The predicted profile in the $\Lambda$CDM cosmology is approximately described by an Einasto profile, meaning that it does not have a cusp but rather a core, where the inner slope slowly converges to zero. Down to one hundredth the total radius, the profile has the right NFW and Einasto forms, being close to the latter down to a radius of about four orders of magnitude less. The inner consistency of the model implies that the density profiles of haloes harbour no information on their past aggregation history. This would explain why major mergers do not alter the typical density profile of virialised objects formed by SI and do not invalidate the peak formalism based on such a formation.Comment: 14 pages, 7 figures. Published in MNRA

Dark matter and cosmic structure

“…Density profiles with this general form have been shown to arise even in the absence of hierarchical growth, for example from HDM initial conditions [134,135] or from sharply truncated initial power spectra [136]. The physical origin of this near-universal shape is not well understood, although many attempts at explanation have been put forward [137][138][139][140][141][142].…”

CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of thez= 0.44 galaxy cluster MACS J1206.2-0847

“…The following slower accretion phase may be responsible for the outer slope of the density profile (Tasitsiomi et al 2004;Lu et al 2006;Hiotelis 2006). Halos would obtain the same, universal density profile independently of details about their collapse (El-Zant 2008;Wang & White 2009) and subsequent merger histories (Dehnen 2005;Kazantzidis et al 2006;El-Zant 2008;Wang & White 2009;Salvador-Solé et al 2012).…”

Predicting the density profiles of the first halos

“…(3) a "virialization" model, put forward by Ref. [73], in which the final radius of a mass shell is determined by enforcing that the shell's enclosed energy be distributed according to the virial theorem.…”

“…Reference [73] developed a model for halo density profiles in which a mass shell freezes where its enclosed energy is virialized. 17 In this model, the final radius of the q shell is r(q) = −(3/10)GM (q) 2 /E(q), where M (q) and E(q) are, respectively, the mass and energy enclosed within the q shell in the linear density field.…”