278 research outputs found
The cosmological free-free signal from galaxy groups and clusters
Using analytical models and cosmological N-body simulations, we study the
free-free radio emission from ionized gas in clusters and groups of galaxies.
The results obtained with the simulations are compared with analytical
predictions based on the mass function and scaling relations. Earlier works
based on analytical models have shown that the average free-free signal from
small haloes (galaxies) during and after the reionization time could be
detected with future experiments as a distortion of the CMB spectrum at low
frequencies ( 5 GHz). We focus on the period after the reionization time
(from redshift up to ) and on haloes that are more massive than in
previous works (groups and clusters). We show how the average signal from
haloes with is less than 10% the signal from the
more abundant and colder smaller mass haloes. However, the individual signal
from the massive haloes could be detected with future experiments opening the
door for a new window to study the intracluster medium.Comment: 11 pages, 7 figure
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
The Dual Origin of Stellar Halos II: Chemical Abundances as Tracers of Formation History
Fully cosmological, high resolution N-Body + SPH simulations are used to
investigate the chemical abundance trends of stars in simulated stellar halos
as a function of their origin. These simulations employ a physically motivated
supernova feedback recipe, as well as metal enrichment, metal cooling and metal
diffusion. As presented in an earlier paper, the simulated galaxies in this
study are surrounded by stellar halos whose inner regions contain both stars
accreted from satellite galaxies and stars formed in situ in the central
regions of the main galaxies and later displaced by mergers into their inner
halos. The abundance patterns ([Fe/H] and [O/Fe]) of halo stars located within
10 kpc of a solar-like observer are analyzed. We find that for galaxies which
have not experienced a recent major merger, in situ stars at the high [Fe/H]
end of the metallicity distribution function are more [alpha/Fe]-rich than
accreted stars at similar [Fe/H]. This dichotomy in the [O/Fe] of halo stars at
a given [Fe/H] results from the different potential wells within which in situ
and accreted halo stars form. These results qualitatively match recent
observations of local Milky Way halo stars. It may thus be possible for
observers to uncover the relative contribution of different physical processes
to the formation of stellar halos by observing such trends in the halo
populations of the Milky Way, and other local L* galaxies.Comment: Version accepted for publication in ApJ Part 1. This version of the
paper has been extended to include a detailed discussion of numerical issue
Neutrinos in Non-linear Structure Formation - The Effect on Halo Properties
We use N-body simulations to find the effect of neutrino masses on halo
properties, and investigate how the density profiles of both the neutrino and
the dark matter components change as a function of the neutrino mass. We
compare our neutrino density profiles with results from the N-one-body method
and find good agreement. We also show and explain why the Tremaine-Gunn bound
for the neutrinos is not saturated. Finally we study how the halo mass function
changes as a function of the neutrino mass and compare our results with the
Sheth-Tormen semi-analytic formulae. Our results are important for surveys
which aim at probing cosmological parameters using clusters, as well as future
experiments aiming at measuring the cosmic neutrino background directly.Comment: 20 pages, 8 figure
Analytic and numerical realisations of a disk galaxy
Recent focus on the importance of cold, unshocked gas accretion in galaxy
formation -- not explicitly included in semi-analytic studies -- motivates the
following detailed comparison between two inherently different modelling
techniques: direct hydrodynamical simulation and semi-analytic modelling. By
analysing the physical assumptions built into the Gasoline simulation, formulae
for the emergent behaviour are derived which allow immediate and accurate
translation of these assumptions to the Galform semi-analytic model. The
simulated halo merger history is then extracted and evolved using these
equivalent equations, predicting a strikingly similar galactic system. This
exercise demonstrates that it is the initial conditions and physical
assumptions which are responsible for the predicted evolution, not the choice
of modelling technique. On this level playing field, a previously published
Galform model is applied (including additional physics such as chemical
enrichment and feedback from active galactic nuclei) which leads to starkly
different predictions.Comment: 15 pages, 15 figure
Evolution of the Dark Matter Phase-Space Density Distributions of LCDM Halos
We study the evolution of phase-space density during the hierarchical
structure formation of LCDM halos. We compute both a spherically-averaged
surrogate for phase-space density (Q) and the coarse-grained distribution
function f(x,v) for dark matter particles that lie within~2 virial radii of
four Milky-Way-sized dark matter halos. The estimated f(x,v) spans over four
decades at any radius. Dark matter particles that end up within two virial
radii of a Milky-Way-sized DM halo at have an approximately Gaussian
distribution in log(f) at early redshifts, but the distribution becomes
increasingly skewed at lower redshifts. The value corresponding to the peak of
the Gaussian decreases as the evolution progresses and is well described by a
power-law in (1+z). The highest values of f are found at the centers of dark
matter halos and subhalos, where f can be an order of magnitude higher than in
the center of the main halo. The power-law Q(r) profile likely reflects the
distribution of entropy (K = sigma^2/rho^{2/3} \propto r^{1.2}), which dark
matter acquires as it is accreted onto a growing halo. The estimated f(x, v),
on the other hand, exhibits a more complicated behavior. Although the median
coarse-grained phase-space density profile F(r) can be approximated by a
power-law in the inner regions of halos and at larger radii the profile
flattens significantly. This is because phase-space density averaged on small
scales is sensitive to the high-f material associated with surviving subhalos,
as well as relatively unmixed material (probably in streams) resulting from
disrupted subhalos, which contribute a sizable fraction of matter at large
radii. (ABRIDGED)Comment: Closely matches version accepted for publicatio
The Origin of Neutral Hydrogen Clouds in Nearby Galaxy Groups: Exploring the Range Of Galaxy Interactions
We combine high resolution N-body simulations with deep observations of
neutral hydrogen (HI) in nearby galaxy groups in order to explore two
well-known theories of HI cloud formation: HI stripping by galaxy interactions
and dark matter minihalos with embedded HI gas. This paper presents new data
from three galaxy groups, Canes Venatici I, NGC 672, and NGC 45, and assembles
data from our previous galaxy group campaign to generate a rich HI cloud
archive to compare to our simulated data.
We find no HI clouds in the Canes Venatici I, NGC 672, or NGC 45 galaxy
groups. We conclude that HI clouds in our detection space are most likely to be
generated through recent, strong galaxy interactions. We find no evidence of HI
clouds associated with dark matter halos above M_HI = 10^6 M_Sun, within +/-
700 km/s of galaxies, and within 50 kpc projected distance of galaxies.Comment: 35 pages, 10 figures, AJ 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
Halo orbits in cosmological disk galaxies : tracers of information history
We analyze the orbits of stars and dark matter particles in the halo of a disk galaxy formed in a cosmological hydrodynamical simulation. The halo is oblate within the inner âź20 kpc and triaxial beyond this radius. About 43% of orbits are short axis tubesâthe rest belong to orbit families that characterize triaxial potentials (boxes, long-axis tubes and chaotic orbits), but their shapes are close to axisymmetric. We find no evidence that the self-consistent distribution function of the nearly oblate inner halo is comprised primarily of axisymmetric short-axis tube orbits. Orbits of all families and both types of particles are highly eccentric, with mean eccentricity ďż˝0.6. We find that randomly selected samples of halo stars show no substructure in âintegrals of motionâ space. However, individual accretion events can clearly be identified in plots of metallicity versus formation time. Dynamically young tidal debris is found primarily on a single type of orbit. However, stars associated with older satellites become chaotically mixed during the formation process (possibly due to scattering by the central bulge and disk, and baryonic processes), and appear on all four types of orbits. We find that the tidal debris in cosmological hydrodynamical simulations experiences significantly more chaotic evolution than in collisionless simulations, making it much harder to identify individual progenitors using phase space coordinates alone. However, by combining information on stellar ages and chemical abundances with the orbital properties of halo stars in the underlying self-consistent potential, the identification of progenitors is likely to be possible
Thin-section Computed Tomography findings before and after azithromycin treatment of neutrophilic reversible lung allograft dysfunction
Recently a novel subgroup of bronchiolitis obliterans syndrome (BOS) has been described in patients after lung transplantation with high neutrophil counts in broncho-alveolar lavage and recovery of lung functional decline with azithromycin treatment. We aimed to describe the thin-section computed tomography (CT) findings of these neutrophilic reversible allograft dysfunction (NRAD) patients before and after azithromycin.status: publishe
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