857 research outputs found
High resolution simulations of the reionization of an isolated Milky Way - M31 galaxy pair
We present the results of a set of numerical simulations aimed at studying
reionization at galactic scale. We use a high resolution simulation of the
formation of the Milky Way-M31 system to simulate the reionization of the local
group. The reionization calculation was performed with the post-processing
radiative transfer code ATON and the underlying cosmological simulation was
performed as part of the CLUES project. We vary the source models to bracket
the range of source properties used in the literature. We investigate the
structure and propagation of the galatic ionization fronts by a visual
examination of our reionization maps. Within the progenitors we find that
reionization is patchy, and proceeds locally inside out. The process becomes
patchier with decreasing source photon output. It is generally dominated by one
major HII region and 1-4 additional isolated smaller bubbles, which eventually
overlap. Higher emissivity results in faster and earlier local reionization. In
all models, the reionization of the Milky Way and M31 are similar in duration,
i.e. between 203 Myr and 22 Myr depending on the source model, placing their
zreion between 8.4 and 13.7. In all models except the most extreme, the MW and
M31 progenitors reionize internally, ignoring each other, despite being
relatively close to each other even during the epoch of reionization. Only in
the case of strong supernova feedback suppressing star formation in haloes less
massive than 10^9 M_sun, and using our highest emissivity, we find that the MW
is reionized by M31.Comment: Accepted for publication in ApJ. 14 pages, 4 figures, 1 tabl
320g Ionization-Heat Cryogenic Detector for Dark Matter Search in the EDELWEISS Experiment
The EDELWEISS experiment used in 2001 a 320g heat-and-ionization cryogenic Ge
detector operated in a low-background environment in the Laboratoire Souterrain
de Modane for direct WIMP detection. This detector presents an increase of more
than 4 times the mass of previous detectors. Calibrations of this detector are
used to determine its energy resolution and fiducial volume, and to optimize
the detector design for the 1kg phase of the EDELWEISS-I experiment. Analysis
of the calibrations and characteristics of a first series of 320g-detectors are
presented.Comment: 4 pages, 3 figure
Le traumatisme de guerre dans le roman europĂ©en (1920 - 1940) : entre âhystĂ©rie masculineâ et âmythe de la guerreâ, problĂšmes dâune histoire culturelle
Actes du XXXVe CongrÚs de la SFLGC, Université de Bourgogne, 2008</p
CPT symmetry and antimatter gravity in general relativity
The gravitational behavior of antimatter is still unknown. While we may be
confident that antimatter is self-attractive, the interaction between matter
and antimatter might be either attractive or repulsive. We investigate this
issue on theoretical grounds. Starting from the CPT invariance of physical
laws, we transform matter into antimatter in the equations of both
electrodynamics and gravitation. In the former case, the result is the
well-known change of sign of the electric charge. In the latter, we find that
the gravitational interaction between matter and antimatter is a mutual
repulsion, i.e. antigravity appears as a prediction of general relativity when
CPT is applied. This result supports cosmological models attempting to explain
the Universe accelerated expansion in terms of a matter-antimatter repulsive
interaction.Comment: 6 pages, to be published in EPL (http://epljournal.edpsciences.org/
"Dark energy" in the Local Void
The unexpected discovery of the accelerated cosmic expansion in 1998 has
filled the Universe with the embarrassing presence of an unidentified "dark
energy", or cosmological constant, devoid of any physical meaning. While this
standard cosmology seems to work well at the global level, improved knowledge
of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently
suggested repulsive-gravity scenario can account for some of the features that
are unexplained by the standard model. Through simple dynamical considerations,
we find that the Local Void could host an amount of antimatter
() roughly equivalent to the mass of a typical
supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this "dark repulsor" can explain the anomalous motion of the
Local Sheet away from the Local Void, as well as several other properties of
nearby galaxies that seem to require void evacuation and structure formation
much faster than expected from the standard model. At the global cosmological
level, gravitational repulsion from antimatter hidden in voids can provide more
than enough potential energy to drive both the cosmic expansion and its
acceleration, with no need for an initial "explosion" and dark energy.
Moreover, the discrete distribution of these dark repulsors, in contrast to the
uniformly permeating dark energy, can also explain dark flows and other
recently observed excessive inhomogeneities and anisotropies of the Universe.Comment: 6 pages, accepted as a Letter to the Editor by Astrophysics and Space
Scienc
Ample filters and Frobenius amplitude
Let be a projective scheme over a field. We show that the vanishing
cohomology of any sequence of coherent sheaves is closely related to vanishing
under pullbacks by the Frobenius morphism. We also compare various definitions
of ample locally free sheaf and show that the vanishing given by the Frobenius
morphism is, in a certain sense, the strongest possible. Our work can be viewed
as various generalizations of the Serre Vanishing Theorem.Comment: 15 pages, major improvement in results, typo fixed in Equation 2.5,
warning footnote added to Lemma 2.
DUSTiER (DUST in the Epoch of Reionization): dusty galaxies in cosmological radiation-hydrodynamical simulations of the Epoch of Reionization with RAMSES-CUDATON
In recent years, interstellar dust has become a crucial topic in the study of
the high and very high redshift Universe. Evidence points to the existence of
high dust masses in massive star forming galaxies already during the Epoch of
Reionization, potentially affecting the escape of ionising photons into the
intergalactic medium. Moreover, correctly estimating dust extinction at UV
wavelengths is essential for precise ultra-violet luminosity function (UVLF)
prediction and interpretation. In this paper, we investigate the impact of dust
on the observed properties of high redshift galaxies, and cosmic reionization.
To this end, we couple a physical model for dust production to the fully
coupled radiation-hydrodynamics cosmological simulation code RAMSES-CUDATON,
and perform a , , simulation, that we call DUSTiER for DUST in
the Epoch of Reionization. It yields galaxies with dust masses and UV slopes
compatible with constraints at z . We find that extinction has a
dramatic impact on the bright end of the UVLF, even as early as , and
our dusty UVLFs are in better agreement with observations than dust-less UVLFs.
The fraction of obscured star formation rises up to 55% at , in
agreement with some of the latest results from ALMA. Finally, we find that dust
reduces the escape of ionising photons from galaxies more massive than (brighter than MAB1600) by >10%, and possibly up to
80-90% for our most massive galaxies. Nevertheless, we find that the ionising
escape fraction is first and foremost set by neutral Hydrogen in galaxies, as
the latter produces transmissions up to 100 times smaller than through dust
alone.Comment: submitted to MNRAS, 1st report received: under revision Have
partially addressed referee's concerns, namely that the model predicts high
dust masses and redder bright galaxies than expected, by discussing this
aspect around the relevant results. Work is being carried out to present a
clearer parameter exploration of the dust mode
Identification of backgrounds in the EDELWEISS-I dark matter search experiment
This paper presents our interpretation and understanding of the different
backgrounds in the EDELWEISS-I data sets. We analyze in detail the several
populations observed, which include gammas, alphas, neutrons, thermal sensor
events and surface events, and try to combine all data sets to provide a
coherent picture of the nature and localisation of the background sources. In
light of this interpretation, we draw conclusions regarding the background
suppression scheme for the EDELWEISS-II phase
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