172 research outputs found
Introducing the Dark Energy Universe Simulation Series (DEUSS)
In this "Invisible Universe" proceedings, we introduce the Dark Energy
Universe Simulation Series (DEUSS) which aim at investigating the imprints of
realistic dark energy models on cosmic structure formation. It represents the
largest dynamical dark energy simulation suite to date in term of spatial
dynamics. We first present the 3 realistic dark energy models (calibrated on
latest SNIa and CMB data): LambdaCDM, quintessence with Ratra-Peebles
potential, and quintessence with Sugra potential. We then isolate various
contributions for non-linear matter power spectra from a series of pre-DEUSS
high-resolution simulations (130 million particles). Finally, we introduce
DEUSS which consist in 9 Grand Challenge runs with 1 billion particles each
thus probing scales from 4 Gpc down to 3 kpc at z=0. Our goal is to make these
simulations available to the community through the "Dark Energy Universe
Virtual Observatory" (DEUVO), and the "Dark Energy Universe Simulations" (DEUS)
consortium.Comment: 6 pages, 3 figures, to appear in the AIP proceedings of the
'Invisible Universe International Conference', UNESCO-Paris, June 29-July 3,
200
Convection and AGN Feedback in Clusters of Galaxies
A number of studies have shown that the convective stability criterion for
the intracluster medium (ICM) is very different from the Schwarzchild criterion
due to the effects of anisotropic thermal conduction and cosmic rays. Building
on these studies, we develop a model of the ICM in which a central active
galactic nucleus (AGN) accretes hot intracluster plasma at the Bondi rate and
produces cosmic rays that cause the ICM to become convectively unstable. The
resulting convection heats the intracluster plasma and regulates its
temperature and density profiles. By adjusting a single parameter in the model
(the size of the cosmic-ray acceleration region), we are able to achieve a good
match to the observed density and temperature profiles in a sample of eight
clusters. Our results suggest that convection is an important process in
cluster cores. An interesting feature of our solutions is that the cooling rate
is more sharply peaked about the cluster center than is the convective heating
rate. As a result, in several of the clusters in our sample, a compact cooling
flow arises in the central region with a size R that is typically a few kpc.
The cooling flow matches onto a Bondi flow at smaller radii. The mass accretion
rate in the Bondi flow is equal to, and controlled by, the rate at which mass
flows in through the cooling flow. Our solutions suggest that the AGN regulates
the mass accretion rate in these clusters by controlling R: if the AGN power
rises above the equilibrium level, R decreases, the mass accretion rate drops,
and the AGN power drops back down to the equilibrium level.Comment: 41 pages, 7 figures, accepted for publication in ApJ. Changes in this
version: extended discussion of Bondi accretion in clusters, better mass
model, new numerical solution
Efficacy of Conventional and Organic Insecticides against Scaphoideus titanus: Field and Semi-Field Trials
Scaphoideus titanus is the main vector of phytoplasmas associated with Flavescence dorée (FD), one of the most serious threats to viticulture in many European countries. To minimize the spread of this disease, mandatory control measures against S. titanus were decided in Europe. In the 1990s, the repeated application of insecticides (mainly organophosphates) proved to be an effective measure to control the vector and the related disease in north-eastern Italy. These insecticides and most of the neonicotinoids were recently banned from European viticulture. Serious FD issues detected in the recent years in northern Italy could be related to the use of less effective insecticides. Trials aimed at evaluating the efficacy of the most used conventional and organic insecticides in the control of S. titanus have been performed in semi-field and field conditions to test this hypothesis. In efficacy trials, carried out in four vineyards, etofenprox and deltamethrin proved to be the best conventional insecticides, while pyrethrins were the most impactful among organic insecticides. Insecticide residual activity was evaluated in semi-field and field conditions. Acrinathrin showed the most significant residual effects in both conditions. In semi-field trials, most of the pyrethroids were associated with good results in terms of residual activity. However, these effects declined in field conditions, probably due to high temperatures. Organic insecticides showed poor results in terms of residual efficacy. Implications of these results in the context of Integrated Pest Management in conventional and organic viticulture are discussed
Imprints of dark energy on cosmic structure formation: II) Non-Universality of the halo mass function
The universality of the halo mass function is investigated in the context of
dark energy cosmologies. This widely used approximation assumes that the mass
function can be expressed as a function of the matter density omega_m and the
rms linear density fluctuation sigma only, with no explicit dependence on the
properties of dark energy or redshift. In order to test this hypothesis we run
a series of 15 high-resolution N-body simulations for different cosmological
models. These consists of three LCDM cosmologies best fitting WMAP-1, 3 and 5
years data, and three toy-models characterized by a Ratra-Peebles quintessence
potential with different slopes and amounts of dark energy density. These toy
models have very different evolutionary histories at the background and linear
level, but share the same sigma8 value. For each of these models we measure the
mass function from catalogues of halos identified in the simulations using the
Friend-of-Friend (FoF) algorithm. We find redshift dependent deviations from a
universal behaviour, well above numerical uncertainties and of non-stochastic
origin, which are correlated with the linear growth factor of the investigated
cosmologies. Using the spherical collapse as guidance, we show that such
deviations are caused by the cosmology dependence of the non-linear collapse
and virialization process. For practical applications, we provide a fitting
formula of the mass function accurate to 5 percents over the all range of
investigated cosmologies. We also derive an empirical relation between the FoF
linking parameter and the virial overdensity which can account for most of the
deviations from an exact universal behavior. Overall these results suggest that
the halo mass function contains unique cosmological information since it
carries a fossil record of the past cosmic evolution.Comment: 21 pages, 19 figures, 5 tables, published in MNRAS. Paper I:
arXiv:0903.549
Cosmological MHD simulations of cluster formation with anisotropic thermal conduction
(abridged) The ICM has been suggested to be buoyantly unstable in the
presence of magnetic field and anisotropic thermal conduction. We perform first
cosmological simulations of galaxy cluster formation that simultaneously
include magnetic fields, radiative cooling and anisotropic thermal conduction.
In isolated and idealized cluster models, the magnetothermal instability (MTI)
tends to reorient the magnetic fields radially. Using cosmological simulations
of the Santa Barbara cluster we detect radial bias in the velocity and magnetic
fields. Such radial bias is consistent with either the inhomogeneous radial gas
flows due to substructures or residual MTI-driven field rearangements that are
expected even in the presence of turbulence. Although disentangling the two
scenarios is challenging, we do not detect excess bias in the runs that include
anisotropic thermal conduction. The anisotropy effect is potentially detectable
via radio polarization measurements with LOFAR and SKA and future X-ray
spectroscopic studies with the IXO. We demonstrate that radiative cooling
boosts the amplification of the magnetic field by about two orders of magnitude
beyond what is expected in the non-radiative cases. At z=0 the field is
amplified by a factor of about 10^6 compared to the uniform magnetic field
evolved due to the universal expansion alone. Interestingly, the runs that
include both radiative cooling and anisotropic thermal conduction exhibit
stronger magnetic field amplification than purely radiative runs at the
off-center locations. In these runs, shallow temperature gradients away from
the cluster center make the ICM neutrally buoyant. The ICM is more easily mixed
in these regions and the winding up of the frozen-in magnetic field is more
efficient resulting in stronger magnetic field amplification.Comment: submitted to ApJ, higher resolution figures available at:
http://www.astro.lsa.umich.edu/~mateuszr
Variação temporal e espacial de fluxo evasivo de CO2 e exportação de carbono orgânico dissolvido em pequenas bacias de drenagem na Amazônia Oriental.
Poster 254. Disponível também on-lie
Observable Signatures of the low-z Circum-Galactic and Inter-Galactic Medium : UV Line Emission in Simulations
We present for the first time predictions for UV line emission of
intergalactic and circumgalactic gas from Adaptive Mesh Resolution (AMR) Large
Scale Structure (LSS) simulations at redshifts 0.3<z<1.2, with specific
emphasis on observability with current and near-future UV instrumentation. In
three transitions of interest (Lya, OVI and CIV) there is a clear bimodality in
the type of objects : the overwhelming majority of flux stems from discrete,
compact sources, while a much larger volume fraction is filled by more tenuous
gas. We characterise both object types with regard to number density, physical
size and shape, brightness, luminosity, velocity structure, mass, temperature,
ionisation state, and metal content. Degrading AMR grids to characteristic
resolutions of available (such as FIREBall) or foreseeable instrumentation,
allows to assess which inferences can be drawn from currently possible
observations, and set foundations to prepare observing strategies for future
missions. In general, the faint emission of the IGM and filamentary structure
remains beyond capabilities of instruments with only short duration exposure
potential (stratospheric balloons), even for optimistic assumptions for Lya,
while the yet fainter metal line transitions for these structures will remain
challenging for long duration exposures (space-based telescopes), mostly due to
low metallicity pushing them more than three orders of magnitudes in brightness
below Lya radiation. For the circum-galactic medium (CGM) the situation is more
promising, and it is foreseeable that in the near future we will not only just
dectect such sources, but the combination of all three lines in addition to
velocity information will yield valuable insight into the physical processes at
hand, illuminating important mechanisms during the formation of galaxies and
their backreaction onto the IGM from whence they formed. (abrigded)Comment: Accepted for publication in MNRAS (2011 November 08, received in
original form 2011 September 14). 27 pages, 19 figures, 3 tables. Some of the
figures have degraded resolution due to file size limitations. For
high-resolution version, please contact the first autho
Summer CO2 evasion from streams and rivers in the Kolyma River basin, north-east Siberia
Inland water systems are generally supersaturated in carbon dioxide (CO2) and are increasingly recognized as playing an important role in the global carbon cycle. The Arctic may be particularly important in this respect, given the abundance of inland waters and carbon contained in Arctic soils; however, a lack of trace gas measurements from small streams in the Arctic currently limits this understanding.We investigated the spatial variability of CO2 evasion during the summer low-flow period from streams and rivers in the northern portion of the Kolyma River basin in north-eastern Siberia. To this end, partial pressure of carbon dioxide (pCO2) and gas exchange velocities (k) were measured at a diverse set of streams and rivers to calculate CO2 evasion fluxes.
We combined these CO2 evasion estimates with satellite remote sensing and geographic information system techniques to calculate total areal CO2 emissions. Our results show that small streams are substantial sources of atmospheric CO2 owing to high pCO2 and k, despite being a small portion of total inland water surface area. In contrast, large rivers were generally near equilibrium with atmospheric CO2. Extrapolating our findings across the Panteleikha-Ambolikha sub-watersheds demonstrated that small streams play a major role in CO2 evasion, accounting for 86% of the total summer CO2 emissions from inland waters within these two sub-watersheds. Further expansion of these regional CO2 emission estimates across time and space will be critical to accurately quantify and understand the role of Arctic streams and rivers in the global carbon budget
Constraining stellar assembly and AGN feedback at the peak epoch of star formation
We study stellar assembly and feedback from active galactic nuclei (AGN)
around the epoch of peak star formation (1<z<2), by comparing hydrodynamic
simulations to rest-frame UV-optical galaxy colours from the Wide Field Camera
3 (WFC3) Early-Release Science (ERS) Programme. Our Adaptive Mesh Refinement
simulations include metal-dependent radiative cooling, star formation, kinetic
outflows due to supernova explosions, and feedback from supermassive black
holes. Our model assumes that when gas accretes onto black holes, a fraction of
the energy is used to form either thermal winds or sub-relativistic
momentum-imparting collimated jets, depending on the accretion rate. We find
that the predicted rest-frame UV-optical colours of galaxies in the model that
includes AGN feedback is in broad agreement with the observed colours of the
WFC3 ERS sample at 1<z<2. The predicted number of massive galaxies also matches
well with observations in this redshift range. However, the massive galaxies
are predicted to show higher levels of residual star formation activity than
the observational estimates, suggesting the need for further suppression of
star formation without significantly altering the stellar mass function. We
discuss possible improvements, involving faster stellar assembly through
enhanced star formation during galaxy mergers while star formation at the peak
epoch is still modulated by the AGN feedback.Comment: 6 pages, 4 figures, accepted for publication in MNRAS Letter
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