51,307 research outputs found
Preparation to the CMB PLANCK data analysis, estimation of the contamination due to the galactic polarized emissions
This work is point of the preparation to the analysis of the PLANCK satellite
data. The PLANCK satellite is an ESA mission which has been launched the 14th
of may 2009 and is dedicaced to the measurement of the Cosmic Microwave
Background (CMB) in temperature and polarization. The presence of diffuse
Galactic polarized emissions disturb the measurement of the CMB anisotropies,
in particular in polarization. Therefore a precise knowledge of these emissions
is needed to obtain the level of accuracy required for PLANCK. In this context,
we have developed and implemented a coherent 3D model of the two mains
polarized Galactic emissions : synchrotron and thermal dust. We have compared
these models to preexisting data: the 23 GHz band of the WMAP data, the 353 GHz
Archeops data and the 408 MHz all-sky continuum survey. We extrapolate these
models to the frequencies where the CMB dominates and we are able to estimate
the contribution of polarized foreground emissions to the polarized CMB
emission measured with PLANCK.Comment: Proceeding of the International Workshop on Cosmic Structure and
Evolution - Cosmology2009, September 23-25, 2009 Bielefeld, German
Bar pattern speed evolution over the last 7 Gyr
The tumbling pattern of a bar is the main parameter characterising its
dynamics. From numerical simulations, its evolution since bar formation is
tightly linked to the dark halo in which the bar is formed through dynamical
friction and angular momentum exchange. Observational measurements of the bar
pattern speed with redshift can restrict models of galaxy formation and bar
evolution. We aim to determine, for the first time, the bar pattern speed
evolution with redshift based on morphological measurements. We have selected a
sample of 44 low inclination ringed galaxies from the SDSS and COSMOS surveys
covering the redshift range 0 <z< 0.8 to investigate the evolution of the bar
pattern speed. We have derived morphological ratios between the deprojected
outer ring radius (R_{ring}) and the bar size (R_{bar}). This quantity is
related to the parameter {\cal R}=R_{CR}/R_{bar} used for classifiying bars in
slow and fast rotators, and allow us to investigate possible differences with
redshift. We obtain a similar distribution of at all redshifts. We do not
find any systematic effect that could be forcing this result. The results
obtained here are compatible with both, the bulk of the bar population (~70%)
being fast-rotators and no evolution of the pattern speed with redshift. We
argue that if bars are long-lasting structures, the results presented here
imply that there has not been a substantial angular momentum exchange between
the bar and halo, as predicted by numerical simulations. In consequence, this
might imply that the discs of these high surface-brightness galaxies are
maximal.Comment: Accepted for publication in A&
Online Inverse Optimal Control for Control-Constrained Discrete-Time Systems on Finite and Infinite Horizons
In this paper, we consider the problem of computing parameters of an
objective function for a discrete-time optimal control problem from state and
control trajectories with active control constraints. We propose a novel method
of inverse optimal control that has a computationally efficient online form in
which pairs of states and controls from given state and control trajectories
are processed sequentially without being stored or processed in batches. We
establish conditions guaranteeing the uniqueness of the objective-function
parameters computed by our proposed method from trajectories with active
control constraints. We illustrate our proposed method in simulation.Comment: 10 pages, 4 figures, Accepted for publication in Automatic
Clumpy Disc and Bulge Formation
We present a set of hydrodynamical/Nbody controlled simulations of isolated
gas rich galaxies that self-consistently include SN feedback and a detailed
chemical evolution model, both tested in cosmological simulations. The initial
conditions are motivated by the observed star forming galaxies at z ~ 2-3. We
find that the presence of a multiphase interstellar media in our models
promotes the growth of disc instability favouring the formation of clumps which
in general, are not easily disrupted on timescales compared to the migration
time. We show that stellar clumps migrate towards the central region and
contribute to form a classical-like bulge with a Sersic index, n > 2. Our
physically-motivated Supernova feedback has a mild influence on clump survival
and evolution, partially limiting the mass growth of clumps as the energy
released per Supernova event is increased, with the consequent flattening of
the bulge profile. This regulation does not prevent the building of a
classical-like bulge even for the most energetic feedback tested. Our Supernova
feedback model is able to establish a self-regulated star formation, producing
mass-loaded outflows and stellar age spreads comparable to observations. We
find that the bulge formation by clumps may coexit with other channels of bulge
assembly such as bar and mergers. Our results suggest that galactic bulges
could be interpreted as composite systems with structural components and
stellar populations storing archaeological information of the dynamical history
of their galaxy.Comment: Accepted for publication in MNRAS - Aug. 20, 201
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