213 research outputs found
Dark Matter Halo Profiles in Scale-Free Cosmologies
We explore the dependence of the central logarithmic slope of dark matter
halo density profiles on the spectral index of the linear matter
power spectrum using cosmological -body simulations of scale-free
models (i.e. ). For each of our simulations we identify
samples of well resolved haloes in dynamical equilibrium and we analyse their
mass profiles. By parameterising the mass profile using a ``generalised''
Navarro, Frenk & White profile in which the central logarithmic slope
is allowed to vary while preserving the asymptotic form at large
radii, we obtain preferred central slopes for haloes in each of our models.
There is a strong correlation between and , such that
becomes shallower as becomes steeper. However, if we normalise our mass
profiles by , the radius at which the logarithmic slope of the density
profile is -2, we find that these differences are no longer present. We
conclude that there is no evidence for convergence to a unique central
asymptotic slope, at least on the scales that we can resolve.Comment: 9 pages, 4 figures. Accepted for publication in MNRA
How do dwarf galaxies acquire their mass & when do they form their stars?
We apply a simple, one-equation, galaxy formation model on top of the halos
and subhalos of a high-resolution dark matter cosmological simulation to study
how dwarf galaxies acquire their mass and, for better mass resolution, on over
10^5 halo merger trees, to predict when they form their stars. With the first
approach, we show that the large majority of galaxies within group- and
cluster-mass halos have acquired the bulk of their stellar mass through gas
accretion and not via galaxy mergers. We deduce that most dwarf ellipticals are
not built up by galaxy mergers. With the second approach, we constrain the star
formation histories of dwarfs by requiring that star formation must occur
within halos of a minimum circular velocity set by the evolution of the
temperature of the IGM, starting before the epoch of reionization. We
qualitatively reproduce the downsizing trend of greater ages at greater masses
and predict an upsizing trend of greater ages as one proceeds to masses lower
than m_crit. We find that the fraction of galaxies with very young stellar
populations (more than half the mass formed within the last 1.5 Gyr) is a
function of present-day mass in stars and cold gas, which peaks at 0.5% at
m_crit=10^6-8 M_Sun, corresponding to blue compact dwarfs such as I Zw 18. We
predict that the baryonic mass function of galaxies should not show a maximum
at masses above 10^5.5, M_Sun, and we speculate on the nature of the lowest
mass galaxies.Comment: 6 pages, to appear in "A Universe of Dwarf Galaxies: Observations,
Theories, Simulations", ed. M. Koleva, P. Prugniel & I. Vauglin, EAS Series
(Paris: EDP
The Effects of X-Ray Feedback from AGN on Host Galaxy Evolution
Hydrodynamic simulations of galaxies with active galactic nuclei (AGN) have
typically employed feedback that is purely local: i.e., an injection of energy
to the immediate neighborhood of the black hole. We perform GADGET-2
simulations of massive elliptical galaxies with an additional feedback
component: an observationally calibrated X-ray radiation field which emanates
from the black hole and heats gas out to large radii from the galaxy center. We
find that including the heating and radiation pressure associated with this
X-ray flux in our simulations enhances the effects which are commonly reported
from AGN feedback. This new feedback model is twice as effective as traditional
feedback at suppressing star formation, produces 3 times less star formation in
the last 6 Gyr, and modestly lowers the final BH mass (30%). It is also
significantly more effective than an X-ray background in reducing the number of
satellite galaxies.Comment: 9 emulateapj pages, 8 figures; accepted to Ap
Bound and unbound substructures in Galaxy-scale Dark Matter haloes
We analyse the coarse-grained phase-space structure of the six Galaxy-scale
dark matter haloes of the Aquarius Project using a state-of-the-art 6D
substructure finder. Within r_50, we find that about 35% of the mass is in
identifiable substructures, predominantly tidal streams, but including about
14% in self-bound subhaloes. The slope of the differential substructure mass
function is close to -2, which should be compared to around -1.9 for the
population of self-bound subhaloes. Near r_50 about 60% of the mass is in
substructures, with about 30% in self-bound subhaloes. The inner 35 kpc of the
highest resolution simulation has only 0.5% of its mass in self-bound
subhaloes, but 3.3% in detected substructure, again primarily tidal streams.
The densest tidal streams near the solar position have a 3-D mass density about
1% of the local mean, and populate the high velocity tail of the velocity
distribution.Comment: Submitted to MNRAS on 12/10/2010, 11 pages, 10 figure
Gene Transfer of Engineered Calmodulin Alleviates Ventricular Arrhythmias in a Calsequestrin-Associated Mouse Model of Catecholaminergic Polymorphic Ventricular Tachycardia
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial arrhythmogenic syndrome characterized by sudden death. There are several genetic forms of CPVT associated with mutations in genes encoding the cardiac ryanodine receptor (RyR2) and its auxiliary proteins including calsequestrin (CASQ2) and calmodulin (CaM). It has been suggested that impairment of the ability of RyR2 to stay closed (ie, refractory) during diastole may be a common mechanism for these diseases. Here, we explore the possibility of engineering CaM variants that normalize abbreviated RyR2 refractoriness for subsequent viral-mediated delivery to alleviate arrhythmias in non-CaM-related CPVT
Automated detection of filaments in the large scale structure of the universe
We present a new method to identify large scale filaments and apply it to a
cosmological simulation. Using positions of haloes above a given mass as node
tracers, we look for filaments between them using the positions and masses of
all the remaining dark-matter haloes. In order to detect a filament, the first
step consists in the construction of a backbone linking two nodes, which is
given by a skeleton-like path connecting the highest local dark matter (DM)
density traced by non-node haloes. The filament quality is defined by a density
and gap parameters characterising its skeleton, and filament members are
selected by their binding energy in the plane perpendicular to the filament.
This membership condition is associated to characteristic orbital times;
however if one assumes a fixed orbital timescale for all the filaments, the
resulting filament properties show only marginal changes, indicating that the
use of dynamical information is not critical for the method. We test the method
in the simulation using massive haloes(h) as
filament nodes. The main properties of the resulting high-quality filaments
(which corresponds to of the detected filaments) are, i) their
lengths cover a wide range of values of up to hMpc, but are mostly
concentrated below 50hMpc; ii) their distribution of thickness peaks at
hMpc and increases slightly with the filament length; iii) their
nodes are connected on average to filaments for nodes; this number increases with the node mass to filaments for nodes.Comment: 17 pages, 13 figures, MNRAS Accepte
N-body simulations with generic non-Gaussian initial conditions I: Power Spectrum and halo mass function
We address the issue of setting up generic non-Gaussian initial conditions
for N-body simulations. We consider inflationary-motivated primordial
non-Gaussianity where the perturbations in the Bardeen potential are given by a
dominant Gaussian part plus a non-Gaussian part specified by its bispectrum.
The approach we explore here is suitable for any bispectrum, i.e. it does not
have to be of the so-called separable or factorizable form. The procedure of
generating a non-Gaussian field with a given bispectrum (and a given power
spectrum for the Gaussian component) is not univocal, and care must be taken so
that higher-order corrections do not leave a too large signature on the power
spectrum. This is so far a limiting factor of our approach. We then run N-body
simulations for the most popular inflationary-motivated non-Gaussian shapes.
The halo mass function and the non-linear power spectrum agree with theoretical
analytical approximations proposed in the literature, even if they were so far
developed and tested only for a particular shape (the local one). We plan to
make the simulations outputs available to the community via the non-Gaussian
simulations comparison project web site
http://icc.ub.edu/~liciaverde/NGSCP.html.Comment: 23 pages, 10 figure
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