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Mesure et implications dynamiques des flux de
matière noire à la surface du viriel des halos de galaxies

Abstract : The success of the concordant cosmological model seem to be difficult to extend
to galactic scales (e.g. the cusp of dark matter profile, or the overproduction of small
structures). It is therefore of prime importance to focus on the dynamics of objects
formed within this paradigm and study them accurately. Yet a quantitative and detailed
accounting of the inner dynamics of galaxies (through high resolution simulation for
instance) seems to be difficult to carry while remaining representative of their cosmic
In order to address this apparent difficulty, the goal of this PhD is to study statistically
the dynamics of galactic systems. This approach aims at relating the observed
distribution of the dynamical properties of galaxies to the caracteristics of environments.
This task requires both an accurate description of the inner dynamical processes, and
a good knowledge of the properties of the environment in which these galaxies are embedded.
In order to fulfill these two constrains, this work relies on an hybrid approach
in which the inner processes are described via the classical analytical tools of galactic
dynamics, while the characteristics of the interaction are extracted from large scale
This PhD restricts itself to the interaction of dark matter halos with their environment.
The exchanges (both accretion and tidal fields) between these objets with
the outer medium are described via the flux of matter through the virial sphere and the projected tidal field. Through this description, the statistical characterization of a
boundary condition is sufficient to characterize the interaction. This halocentric view
allows in particular a retain the angular and kinetic information required to compute
the inner dynamical response of halos.
The inner dynamics is described in the regime of weak interaction through a non
linear perturbative description of the response of an open non collisional system. This
theory should account for a proper description of phenomena such as dynamical friction
of tidal stripping. Through an extension of the standard “matrix method” which
describes the dynamics in angle-action space, this technique translates directly the statistical
features of the boundary into the core of the halo. This “statistical propagation”
does not rely on the knowledge of the individual realizations of interacting systems, but
dynamical consistency require a full knowledge of the statistical properties of accretion,
and its tidal field, together with their cross dependence (through the knowledge of temporal
cross correlations). The secular evolution of the halo in the regime of recurrent
interactions is also described via a quasilinear formalism. The secular evolution of the
distribution function of the halo is investigated as a slow diffusion of the underlying
orbits induced by the presence of the accreted material.
The properties of accretion and the tidal field are derived from a large set of cosmological
simulations in order to reduce the effect of cosmic variance. These measurements
yield a quantitative description of the the interactions which is consistent with the diversity
of configuration space. These simulations only explore the regime of weak interaction
at redshifts below one. A detailed measurement of the mass flux density at the virial
radius has led to a quantitative description of the level of anisotropy of accretion towards
dark halos. This flux measurement was also completed by a thorough description of the
satellite distribution around halos, which confirmed the excess of equatorial accretion at
a level of 15%. It was interpreted as filamentary flows on the scales of halos. The
properties of the flux densities of accreted dark matter were then investigated in more
detail through a description customized to statistical propagation. The kinematic properties
of particles crossing the virial radius show a clear cut between the newly accreted
material and that which had already crossed the sphere at earlier time and had already
interacted with the halo. This difference can be traced through their trajectories or their
characteristic velocities. The angular temporal correlation of the tidal potential at the
virial radius suggest that the tidal field is stationary and strongly quadrupolar, tracing
the dark matter distribution in the peripheral regions of the halo. The corresponding
correlations for the mass flux density show in particular time invariance of the dark
matter power spectrum at the virial radius.
A short study of the distribution of metals within substructures shows how observational
measurements constrain the statistical distribution of matter within the halo.
Generally, linking the statistical properties of the environment and the variety of
dynamical responses should open a large field of possible applications. First the statistical
distribution of dark matter within halos can be predicted through the knowledge
of these fluxes. Conversely, the observational tracers of matter (X ray emission, SZ,
gravitational lensing, absorptions lines in QSO) provide constraints on the properties of
these fluxes, but also on the underlying dark matter halo model (e.g. mass profile) and
on the biases corresponding to each tracer (M/L ratios for instance). Finally, once the
statistical propagation has been validated, it should be possible to dynamically invert
for the past accretion history of a given halo from its current state.
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Contributor : Dominique Aubert <>
Submitted on : Monday, October 30, 2006 - 5:42:51 PM
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  • HAL Id : tel-00110561, version 1


Dominique Aubert. Mesure et implications dynamiques des flux de
matière noire à la surface du viriel des halos de galaxies. Astrophysique [astro-ph]. Université Paris Sud - Paris XI, 2005. Français. ⟨tel-00110561⟩



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