5,367 research outputs found
Interactions of Satellite Galaxies in Cosmological Dark Matter Halos
We present a statistical analysis of the interactions between satellite
galaxies in cosmological dark matter halos taken from fully self-consistent
high-resolution simulations of galaxy clusters. We show that the number
distribution of satellite encounters has a tail that extends to as many as 3-4
encounters per orbit. On average 30% of the substructure population had at
least one encounter (per orbit) with another satellite galaxy. However, this
result depends on the age of the dark matter host halo with a clear trend for
more interactions in younger systems. We also report a correlation between the
number of encounters and the distance of the satellites to the centre of the
cluster: satellite galaxies closer to the centre experience more interactions.
However, this can be simply explained by the radial distribution of the
substructure population and merely reflects the fact that the density of
satellites is higher in those regions.
In order to find substructure galaxies we applied (and present) a new
technique based upon the N-body code MLAPM. This new halo finder MHF
(MLAPM's-Halo-Finder) acts with exactly the same accuracy as the N-body code
itself and is therefore free of any bias and spurious mismatch between
simulation data and halo finding precision related to numerical effects.Comment: 6 pages, 4 figures, accepted by PASA (refereed contribution to the
5th Galactic Chemodynamics workshop, July 2003
Mapping Substructures in Dark Matter Halos
We present a detailed study of the real and integrals-of-motion space
distributions of a satellite obtained from a self-consistent high-resolution
simulation of a galaxy cluster and re-simulated using various analytical halo
potentials. We found that the disrupted satellite appears as a coherent
structure in integrals-of-motion space in all models (``live'' and analytical
potential) although the distribution is significantly smeared for the live host
halo. Further the primary mechanism for this smearing is the mass growth of the
host, which changes both the energy and angular momentum of the satellite
debris. Hence, this must be considered when searching for (stellar) streams
with future observational experiments such as RAVE and GAIA.Comment: 5 pages, 6 figures, MNRAS accepted - minor editing without changing
the conclusions, a high-resolution version of the paper is available from
http://astronomy.swin.edu.au/~sgill/downloads/downloads.htm
Cosmology on a Mesh
An adaptive multi grid approach to simulating the formation of structure from
collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle
Mesh) is one of the most efficient serial codes available on the cosmological
'market' today. As part of Swinburne University's role in the development of
the Square Kilometer Array, we are implementing hydrodynamics, feedback, and
radiative transfer within the MLAPM adaptive mesh, in order to simulate
baryonic processes relevant to the interstellar and intergalactic media at high
redshift. We will outline our progress to date in applying the existing MLAPM
to a study of the decay of satellite galaxies within massive host potentials.Comment: 3 pages, 2 figures, to appear in the proceedings of "The IGM/Galaxy
Connection - The Distribution of Baryons at z=0", ed. M. Putman & J.
Rosenber
The importance of interactions for mass loss from satellite galaxies in cold dark matter haloes
We investigate the importance of interactions between dark matter substructures for the mass loss they suffer whilst orbiting within a sample of high-resolution galaxy cluster mass cold dark matter (CDM) haloes formed in cosmological N-body simulations. We have defined a quantitative measure that gauges the degree to which interactions are responsible for mass loss from substructures. This measure indicates that interactions are more prominent in younger systems when compared to older more relaxed systems. We show that this is due to the increased number of encounters a satellite experiences and a higher mass fraction in satellites. This is in spite of the uniformity in the distributions of relative distances and velocities of encounters between substructures within the different host systems in our sample. Using a simple model to relate the net force felt by a single satellite to the mass loss it suffers, we show that interactions with other satellites account for âŒ30 per cent of the total mass loss experienced over its lifetime. The relation between the age of the host and the importance of interactions increases the scatter about this mean value from âŒ25 per cent for the oldest to âŒ45 per cent for the youngest system we have studied. We conclude that satellite interactions play a vital role in the evolution of substructure in dark matter haloes and that a significant fraction of the tidally stripped material can be attributed to these interaction
The Importance of Interactions for Mass Loss from Satellite Galaxies in Cold Dark Matter Haloes
We investigate the importance of interactions between dark matter
substructures for the mass loss they suffer whilst orbiting within a sample of
high resolution galaxy cluster mass Cold Dark Matter haloes formed in
cosmological N-body simulations. We have defined a quantitative measure that
gauges the degree to which interactions are responsible for mass loss from
substructures. This measure indicates that interactions are more prominent in
younger systems when compared to older more relaxed systems. We show that this
is due to the increased number of encounters a satellite experiences and a
higher mass fraction in satellites. This is in spite of the uniformity in the
distributions of relative distances and velocities of encounters between
substructures within the different host systems in our sample. Using a simple
model to relate the net force felt by a single satellite to the mass loss it
suffers, we show that interactions with other satellites account for ~30% of
the total mass loss experienced over its lifetime. The relation between the age
of the host and the importance of interactions increases the scatter about this
mean value from ~25% for the oldest to ~45% for the youngest system we have
studied. We conclude that satellite interactions play a vital role in the
evolution of substructure in dark matter halos and that a significant fraction
of the tidally stripped material can be attributed to these interactions.Comment: accepted for publication in MNRAS, 11 pages, 10 figure
Radial Alignment in Simulated Clusters
Observational evidence for the radial alignment of satellites with their dark
matter host has been accumulating steadily in the past few years. The effect is
seen over a wide range of scales, from massive clusters of galaxies down to
galaxy-sized systems, yet the underlying physical mechanism has still not been
established. To this end, we have carried out a detailed analysis of the shapes
and orientations of dark matter substructures in high-resolution N-body
cosmological simulations. We find a strong tendency for radial alignment of the
substructure with its host halo: the distribution of halo major axes is very
anisotropic, with the majority pointing towards the center of mass of the host.
The alignment peaks once the sub-halo has passed the virial radius of the host
for the first time, but is not subsequently diluted, even after the halos have
gone through as many as four pericentric passages. This evidence points to the
existence of a very rapid dynamical mechanism acting on these systems and we
argue that tidal torquing throughout their orbits is the most likely candidate.Comment: v2: 13 pages, 10 figures, ApJ in press. Revisions include a new
section (4.2) comparing our results with observations, and a few added
reference
The evolution of substructure II: linking dynamics to environment
We present results from a series of high-resolution N-body simulations that
focus on the formation and evolution of eight dark matter halos, each of order
a million particles within the virial radius. We follow the time evolution of
hundreds of satellite galaxies with unprecedented time resolution, relating
their physical properties to the differing halo environmental conditions. The
self-consistent cosmological framework in which our analysis was undertaken
allows us to explore satellite disruption within live host potentials, a
natural complement to earlier work conducted within static potentials. Our host
halos were chosen to sample a variety of formation histories, ages, and
triaxialities; despite their obvious differences, we find striking similarities
within the associated substructure populations. Namely, all satellite orbits
follow nearly the same eccentricity distribution with a correlation between
eccentricity and pericentre. We also find that the destruction rate of the
substructure population is nearly independent of the mass, age, and triaxiality
of the host halo. There are, however, subtle differences in the velocity
anisotropy of the satellite distribution. We find that the local velocity bias
at all radii is greater than unity for all halos and this increases as we move
closer to the halo centre, where it varies from 1.1 to 1.4. For the global
velocity bias we find a small but slightly positive bias, although when we
restrict the global velocity bias calculation to satellites that have had at
least one orbit, the bias is essentially removed.Comment: 14 pages, 14 figures, MNRAS in pres
The evolution of substructure III: the outskirts of clusters
We present an investigation of satellite galaxies in the outskirts of galaxy
clusters taken from a series of high-resolution N-body simulations. We focus on
the so-called "backsplash population", i.e. satellite galaxies that once were
inside the virial radius of the host but now reside beyond it. We find that
this population is significant in number and needs to be appreciated when
interpreting the various galaxy morphology environmental relationships and
decoupling the degeneracy between nature and nurture. Specifically, we find
that approximately half of the galaxies with current clustercentric distance in
the interval 1-2 virial radii of the host are backsplash galaxies which once
penetrated deep into the cluster potential, with 90% of these entering to
within 50% of the virial radius. These galaxies have undergone significant
tidal disruption, loosing on average 40% of their mass. This results in a mass
function for the backsplash population different to those galaxies infalling
for the first time. We further show that these two populations are
kinematically distinct and should be observable within existent spectroscopic
surveys.Comment: 7 pages, 8 figures, MNRAS accepted - minor editing without changing
the conclusion
Anisotropy in the Distribution of Satellite Galaxy Orbits
Nearby clusters such as Virgo and Coma possess galaxy distributions which
tend to be aligned with the principal axis of the cluster itself. This has also
been confirmed by a recent statistical analysis of some 300 Abell clusters
where the effect has been linked to the dynamical state of the cluster.
Moreover, the orbits of satellite galaxies in galactic systems like our own
Milky Way also demonstrate a high degree of anisotropy - the so-called Holmberg
effect, the origin of which has been the subject of debate for more than 30
years. This study presents the analysis of cosmological simulations focusing on
the orbits of satellite galaxies within dark matter halos. The apocentres of
the orbits of these satellites are preferentially found within a cone of
opening angle ~40 around the major axis of the host halo, in accordance with
the observed anisotropy found in galaxy clusters. We do, however, note that a
link to the dynamical age of the cluster is not well established as both our
oldest dark matter halos do show a clear anisotropy signal. Further analysis
connects this distribution to the infall pattern of satellites along the
filaments: the orbits are determined rather by the environment of the host halo
than some "dynamical selection" during their life within the host's virial
radius.Comment: 6 pages, 2 figures, ApJ in pres
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