5,290 research outputs found
Satellites of Simulated Galaxies: survival, merging, and their relation to the dark and stellar halos
We study the population of satellite galaxies formed in a suite of
N-body/gasdynamical simulations of galaxy formation in a LCDM universe. We find
little spatial or kinematic bias between the dark matter and the satellite
population. The velocity dispersion of the satellites is a good indicator of
the virial velocity of the halo: \sigma_{sat}/V_{vir}=0.9 +/- 0.2. Applied to
the Milky Way and M31 this gives V_{vir}^{MW}=109 +/- 22$ km/s and
V_{vir}^{M31} = 138 +/- 35 km/s, respectively, substantially lower than the
rotation speed of their disk components. The detailed kinematics of simulated
satellites and dark matter are also in good agreement. By contrast, the stellar
halo of the simulated galaxies is kinematically and spatially distinct from the
population of surviving satellites. This is because the survival of a satellite
depends on mass and on time of accretion; surviving satellites are biased
toward low-mass systems that have been recently accreted by the galaxy. Our
results support recent proposals for the origin of the systematic differences
between stars in the Galactic halo and in Galactic satellites: the elusive
``building blocks'' of the Milky Way stellar halo were on average more massive,
and were accreted (and disrupted) earlier than the population of dwarfs that
has survived self-bound until the present.Comment: 13 pages, 11 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Cosmic M\'enage \`a Trois: The Origin of Satellite Galaxies On Extreme Orbits
We examine the orbits of satellite galaxies identified in a suite of
N-body/gasdynamical simulations of the formation of galaxies in a LCDM
universe. Most satellites follow conventional orbits; after turning around,
they accrete into their host halo and settle on orbits whose apocentric radii
are steadily eroded by dynamical friction. However, a number of outliers are
also present, we find that ~1/3 of satellites identified at are on
unorthodox orbits, with apocenters that exceed their turnaround radii. This
population of satellites on extreme orbits consists typically of the faint
member of a satellite pair that has been ejected onto a highly-energetic orbit
during its first approach to the primary. Since the concurrent accretion of
multiple satellite systems is a defining feature of hierarchical models of
galaxy formation, we speculate that this three-body ejection mechanism may be
the origin of (i) some of the newly discovered high-speed satellites around M31
(such as Andromeda XIV); (ii) some of the distant fast-receding Local Group
members, such as Leo I; and (iii) the oddly isolated dwarf spheroidals Cetus
and Tucana in the outskirts of the Local Group. Our results suggest that care
must be exercised when using the orbits of the most weakly bound satellites to
place constraints on the total mass of the Local Group.Comment: 10 pages, 6 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
Density distribution of particles upon jamming after an avalanche in a 2D silo
We present a complete analysis of the density distribution of particles in a
two dimensional silo after discharge. Simulations through a pseudo-dynamic
algorithm are performed for filling and subsequent discharge of a plane silo.
Particles are monosized hard disks deposited in the container and subjected to
a tapping process for compaction. Then, a hole of a given size is open at the
bottom of the silo and the discharge is triggered. After a clogging at the
opening is produced, and equilibrium is restored, the final distribution of the
remaining particles at the silo is analyzed by dividing the space into cells
with different geometrical arrangements to visualize the way in which the
density depression near the opening is propagated throughout the system. The
different behavior as a function of the compaction degree is discussed.Comment: 11 pages, 10 figure
Quantum gauge boson propagators in the light front
Gauge fields in the light front are traditionally addressed via the
employment of an algebraic condition in the Lagrangian density,
where is the gauge field (Abelian or non-Abelian) and is the
external, light-like, constant vector which defines the gauge proper. However,
this condition though necessary is not sufficient to fix the gauge completely;
there still remains a residual gauge freedom that must be addressed
appropriately. To do this, we need to define the condition with . The implementation of this
condition in the theory gives rise to a gauge boson propagator (in momentum
space) leading to conspicuous non-local singularities of the type where . These singularities must be conveniently
treated, and by convenient we mean not only matemathically well-defined but
physically sound and meaningfull as well. In calculating such a propagator for
one and two noncovariant gauge bosons those singularities demand from the
outset the use of a prescription such as the Mandelstam-Leibbrandt (ML) one. We
show that the implementation of the ML prescription does not remove certain
pathologies associated with zero modes. However we present a causal,
singularity-softening prescription and show how to keep causality from being
broken without the zero mode nuisance and letting only the propagation of
physical degrees of freedom.Comment: 10 page
Satellite Galaxies and Fossil Groups in the Millennium Simulation
We use a semianalytic galaxy catalogue constructed from the Millennium
Simulation to study the satellites of isolated galaxies in the LCDM cosmogony.
This sample (~80,000$ bright primaries, surrounded by ~178,000 satellites)
allows the characterization, with minimal statistical uncertainty, of the
dynamical properties of satellite/primary galaxy systems in a LCDM universe. We
find that, overall, the satellite population traces the dark matter rather
well: its spatial distribution and kinematics may be approximated by an NFW
profile with a mildly anisotropic velocity distribution. Their spatial
distribution is also mildly anisotropic, with a well-defined ``anti-Holmberg''
effect that reflects the misalignment between the major axis and angular
momentum of the host halo. The isolation criteria for our primaries picks not
only galaxies in sparse environments, but also a number of primaries at the
centre of ''fossil'' groups. We find that the abundance and luminosity function
of these unusual systems are in reasonable agreement with the few available
observational constraints. We recover the expected L_{host} \sigma_{sat}^3
relation for LCDM models for truly-isolated primaries. Less strict primary
selection, however, leads to substantial modification of the scaling relation.
Our analysis also highlights a number of difficulties afflicting studies that
rely on blind stacking of satellite systems to constrain the mean halo mass of
the primary galaxies.Comment: 18 pages, 14 figures, MNRAS in press. Accepted version with minor
changes. Version with high resolution figures available at:
http://www.astro.uvic.ca/~lsales/SatPapers/SatPapers.htm
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