57 research outputs found
Streams Going Notts: The tidal debris finder comparison project
While various codes exist to systematically and robustly find haloes and
subhaloes in cosmological simulations (Knebe et al., 2011, Onions et al.,
2012), this is the first work to introduce and rigorously test codes that find
tidal debris (streams and other unbound substructure) in fully cosmological
simulations of structure formation. We use one tracking and three non-tracking
codes to identify substructure (bound and unbound) in a Milky Way type
simulation from the Aquarius suite (Springel et al., 2008) and post-process
their output with a common pipeline to determine the properties of these
substructures in a uniform way. By using output from a fully cosmological
simulation, we also take a step beyond previous studies of tidal debris that
have used simple toy models. We find that both tracking and non-tracking codes
agree well on the identification of subhaloes and more importantly, the {\em
unbound tidal features} associated with them. The distributions of basic
properties of the total substructure distribution (mass, velocity dispersion,
position) are recovered with a scatter of . Using the tracking code as
our reference, we show that the non-tracking codes identify complex tidal
debris with purities of . Analysing the results of the substructure
finders, we find that the general distribution of {\em substructures} differ
significantly from the distribution of bound {\em subhaloes}. Most importantly,
both bound and unbound {\em substructures} together constitute of the
host halo mass, which is a factor of higher than the fraction in
self-bound {\em subhaloes}. However, this result is restricted by the remaining
challenge to cleanly define when an unbound structure has become part of the
host halo. Nevertheless, the more general substructure distribution provides a
more complete picture of a halo's accretion history.Comment: 19 pages, 12 figures, accepted for publication in MNRA
Galaxies going MAD: The Galaxy-Finder Comparison Project
With the ever increasing size and complexity of fully self-consistent
simulations of galaxy formation within the framework of the cosmic web, the
demands upon object finders for these simulations has simultaneously grown. To
this extent we initiated the Halo Finder Comparison Project that gathered
together all the experts in the field and has so far led to two comparison
papers, one for dark matter field haloes (Knebe et al. 2011), and one for dark
matter subhaloes (Onions et al. 2012). However, as state-of-the-art simulation
codes are perfectly capable of not only following the formation and evolution
of dark matter but also account for baryonic physics (e.g. hydrodynamics, star
formation, feedback) object finders should also be capable of taking these
additional processes into consideration. Here we report on a comparison of
codes as applied to the Constrained Local UniversE Simulation (CLUES) of the
formation of the Local Group which incorporates much of the physics relevant
for galaxy formation. We compare both the properties of the three main galaxies
in the simulation (representing the MW, M31, and M33) as well as their
satellite populations for a variety of halo finders ranging from phase-space to
velocity-space to spherical overdensity based codes, including also a mere
baryonic object finder. We obtain agreement amongst codes comparable to (if not
better than) our previous comparisons, at least for the total, dark, and
stellar components of the objects. However, the diffuse gas content of the
haloes shows great disparity, especially for low-mass satellite galaxies. This
is primarily due to differences in the treatment of the thermal energy during
the unbinding procedure. We acknowledge that the handling of gas in halo
finders is something that needs to be dealt with carefully, and the precise
treatment may depend sensitively upon the scientific problem being studied.Comment: 14 interesting pages, 17 beautiful figures, and 2 informative tables
accepted for publication in MNRAS (matches published version
Subhaloes gone Notts: the clustering properties of subhaloes
We present a study of the substructure finder dependence of subhalo clustering in the Aquarius Simulation. We run 11 different subhalo finders on the haloes of the Aquarius Simulation and study their differences in the density profile, mass fraction and two-point correlation function of subhaloes in haloes. We also study the mass and vmax dependence of subhalo clustering. As the Aquarius Simulation has been run at different resolutions, we study the convergence with higher resolutions. We find that the agreement between finders is at around the 10 per cent level inside R200 and at intermediate resolutions when a mass threshold is applied, and better than 5 per cent when vmax is restricted instead of mass. However, some discrepancies appear in the highest resolution, underlined by an observed resolution dependence of subhalo clustering. This dependence is stronger for the smallest subhaloes, which are more clustered in the highest resolution, due to the detection of subhaloes within subhaloes (the sub-subhalo term). This effect modifies the mass dependence of clustering in the highest resolutions. We discuss implications of our results for models of subhalo clustering and their relation with galaxy clustering
Solving the puzzle of subhalo spins
Investigating the spin parameter distribution of subhalos in two high-resolution isolated halo simulations, recent work by Onions et al. suggested that typical subhalo spins are consistently lower than the spin distribution found for field halos. To further examine this puzzle, we have analyzed simulations of a cosmological volume with sufficient resolution to resolve a significant subhalo population. We confirm the result of Onions et al. and show that the typical spin of a subhalo decreases with decreasing mass and increasing proximity to the host halo center. We interpret this as the growing influence of tidal stripping in removing the outer layers, and hence the higher angular momentum particles, of the subhalos as they move within the host potential. Investigating the redshift dependence of this effect, we find that the typical subhalo spin is smaller with decreasing redshift. This indicates a temporal evolution, as expected in the tidal stripping scenario
Subhaloes gone Notts: subhaloes as tracers of the dark matter halo shape
We study the shapes of subhalo distributions from four dark-matter-only simulations of Milky Way-type haloes. Comparing the shapes derived from the subhalo distributions at high resolution to those of the underlying dark matter fields, we find the former to be more triaxial if the analysis is restricted to massive subhaloes. For three of the four analysed haloes, the increased triaxiality of the distributions of massive subhaloes can be explained by a systematic effect caused by the low number of objects. Subhaloes of the fourth halo show indications for anisotropic accretion via their strong triaxial distribution and orbit alignment with respect to the dark matter field. These results are independent of the employed subhalo finder. Comparing the shape of the observed Milky Way satellite distribution to those of high-resolution subhalo samples from simulations, we find agreement for samples of bright satellites, but significant deviations if faint satellites are included in the analysis. These deviations might result from observational incompleteness
SubHaloes going Notts: The SubHalo-Finder Comparison Project
We present a detailed comparison of the substructure properties of a single
Milky Way sized dark matter halo from the Aquarius suite at five different
resolutions, as identified by a variety of different (sub-)halo finders for
simulations of cosmic structure formation. These finders span a wide range of
techniques and methodologies to extract and quantify substructures within a
larger non-homogeneous background density (e.g. a host halo). This includes
real-space, phase-space, velocity-space and time- space based finders, as well
as finders employing a Voronoi tessellation, friends-of-friends techniques, or
refined meshes as the starting point for locating substructure.A common
post-processing pipeline was used to uniformly analyse the particle lists
provided by each finder. We extract quantitative and comparable measures for
the subhaloes, primarily focusing on mass and the peak of the rotation curve
for this particular study. We find that all of the finders agree extremely well
on the presence and location of substructure and even for properties relating
to the inner part part of the subhalo (e.g. the maximum value of the rotation
curve). For properties that rely on particles near the outer edge of the
subhalo the agreement is at around the 20 per cent level. We find that basic
properties (mass, maximum circular velocity) of a subhalo can be reliably
recovered if the subhalo contains more than 100 particles although its presence
can be reliably inferred for a lower particle number limit of 20. We finally
note that the logarithmic slope of the subhalo cumulative number count is
remarkably consistent and <1 for all the finders that reached high resolution.
If correct, this would indicate that the larger and more massive, respectively,
substructures are the most dynamically interesting and that higher levels of
the (sub-)subhalo hierarchy become progressively less important.Comment: 16 pages, 7 figures, 2 tables, Accepted for MNRA
In vitro and in vivo antifungal profile of a novel and long acting inhaled azole, PC945, on Aspergillus fumigatus infection
The profile of PC945, a novel triazole antifungal, designed for administration via inhalation, hasbeen assessed in a range of in vitro and in vivo studies. PC945 was characterized as a potent, tight-binding inhibitor of Aspergillus fumigatus sterol 14α-demethylase (CYP51A and CYP51B)activity.In addition, when A. fumigatus hyphae or human bronchial cells were treated with PC945, and thenwashed, PC945 was found to be quickly absorbed into both target and non-target cells and toproduce persistent antifungal effects. In temporarily neutropenic immunocompromised miceinfected with A. fumigatus intranasally, 50% of the animals survived until day 7 when treatedintranasally with PC945 at 0.56 μg/mouse, while posaconazole showed similar effects (44%) at14 μg/mouse. This profile affirms that topical treatment with PC945 should provide potentantifungal activity in the lung
Effects of school-based interventions on mental health stigmatization: a systematic review
Stigmatizing, or discriminatory, perspectives and behaviour, which target individuals on the basis of their mental health, are observed in even the youngest school children. We conducted a systematic review of the published and unpublished, scientific literature concerning the benefits and harms of school-based interventions, which were directed at students 18 years of age or younger to prevent or eliminate such stigmatization. Forty relevant studies were identified, yet only a qualitative synthesis was deemed appropriate. Five limitations within the evidence base constituted barriers to drawing conclusive inferences about the effectiveness and harms of school-based interventions: poor reporting quality, a dearth of randomized controlled trial evidence, poor methods quality for all research designs, considerable clinical heterogeneity, and inconsistent or null results. Nevertheless, certain suggestive evidence derived both from within and beyond our evidence base has allowed us to recommend the development, implementation and evaluation of a curriculum, which fosters the development of empathy and, in turn, an orientation toward social inclusion and inclusiveness. These effects may be achieved largely by bringing especially but not exclusively the youngest children into direct, structured contact with an infant, and likely only the oldest children and youth into direct contact with individuals experiencing mental health difficulties. The possible value of using educational activities, materials and contents to enhance hypothesized benefits accruing to direct contact also requires investigation. Overall, the curriculum might serve as primary prevention for some students and as secondary prevention for others
Solving the puzzle of subhalo spins
Investigating the spin parameter distribution of subhalos in two high-resolution isolated halo simulations, recent work by Onions et al. suggested that typical subhalo spins are consistently lower than the spin distribution found for field halos. To further examine this puzzle, we have analyzed simulations of a cosmological volume with sufficient resolution to resolve a significant subhalo population. We confirm the result of Onions et al. and show that the typical spin of a subhalo decreases with decreasing mass and increasing proximity to the host halo center. We interpret this as the growing influence of tidal stripping in removing the outer layers, and hence the higher angular momentum particles, of the subhalos as they move within the host potential. Investigating the redshift dependence of this effect, we find that the typical subhalo spin is smaller with decreasing redshift. This indicates a temporal evolution, as expected in the tidal stripping scenario
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