492 research outputs found
Bayesian 3d velocity field reconstruction with VIRBIuS
I describe a new Bayesian based algorithm to infer the full three dimensional
velocity field from observed distances and spectroscopic galaxy catalogues. In
addition to the velocity field itself, the algorithm reconstructs true
distances, some cosmological parameters and specific non-linearities in the
velocity field. The algorithm takes care of selection effects, miscalibration
issues and can be easily extended to handle direct fitting of, e.g., the
inverse Tully-Fisher relation. I first describe the algorithm in details
alongside its performances. This algorithm is implemented in the VIRBIuS
(VelocIty Reconstruction using Bayesian Inference Software) software package. I
then test it on different mock distance catalogues with a varying complexity of
observational issues. The model proved to give robust measurement of velocities
for mock catalogues of 3,000 galaxies. I expect the core of the algorithm to
scale to tens of thousands galaxies. It holds the promises of giving a better
handle on future large and deep distance surveys for which individual errors on
distance would impede velocity field inference.Comment: 28 pages, 13 figures, accepted by MNRA
Bayesian power-spectrum inference with foreground and target contamination treatment
This work presents a joint and self-consistent Bayesian treatment of various
foreground and target contaminations when inferring cosmological power-spectra
and three dimensional density fields from galaxy redshift surveys. This is
achieved by introducing additional block sampling procedures for unknown
coefficients of foreground and target contamination templates to the previously
presented ARES framework for Bayesian large scale structure analyses. As a
result the method infers jointly and fully self-consistently three dimensional
density fields, cosmological power-spectra, luminosity dependent galaxy biases,
noise levels of respective galaxy distributions and coefficients for a set of a
priori specified foreground templates. In addition this fully Bayesian approach
permits detailed quantification of correlated uncertainties amongst all
inferred quantities and correctly marginalizes over observational systematic
effects. We demonstrate the validity and efficiency of our approach in
obtaining unbiased estimates of power-spectra via applications to realistic
mock galaxy observations subject to stellar contamination and dust extinction.
While simultaneously accounting for galaxy biases and unknown noise levels our
method reliably and robustly infers three dimensional density fields and
corresponding cosmological power-spectra from deep galaxy surveys. Further our
approach correctly accounts for joint and correlated uncertainties between
unknown coefficients of foreground templates and the amplitudes of the
power-spectrum. An effect amounting up to percent correlations and
anti-correlations across large ranges in Fourier space.Comment: 15 pages, 11 figure
The 2M++ galaxy redshift catalogue
Peculiar velocities arise from gravitational instability, and thus are linked
to the surrounding distribution of matter. In order to understand the motion of
the Local Group with respect to the Cosmic Microwave Background, a deep all-sky
map of the galaxy distribution is required. Here we present a new redshift
compilation of 69~160 galaxies, dubbed 2M++, to map large-scale structures of
the Local Universe over nearly the whole sky, and reaching depths of K <= 12.5,
or 200 Mpc/h. The target catalogue is based on the Two-Micron-All-Sky Extended
Source Catalog (2MASS-XSC). The primary sources of redshifts are the 2MASS
Redshift Survey, the 6dF galaxy redshift survey and the Sloan Digital Sky
Survey (DR7). We assess redshift completeness in each region and compute the
weights required to correct for redshift incompleteness and apparent magnitude
limits, and discuss corrections for incompleteness in the Zone of Avoidance. We
present the density field for this survey, and discuss the importance of
large-scale structures such as the Shapley Concentration.Comment: 19 pages, 15 figures, 6 tables, submitted to MNRA
Bayesian inference of CMB gravitational lensing
The Planck satellite, along with several ground based telescopes, have mapped
the cosmic microwave background (CMB) at sufficient resolution and
signal-to-noise so as to allow a detection of the subtle distortions due to the
gravitational influence of the intervening matter distribution. A natural
modeling approach is to write a Bayesian hierarchical model for the lensed CMB
in terms of the unlensed CMB and the lensing potential. So far there has been
no feasible algorithm for inferring the posterior distribution of the lensing
potential from the lensed CMB map. We propose a solution that allows efficient
Markov Chain Monte Carlo sampling from the joint posterior of the lensing
potential and the unlensed CMB map using the Hamiltonian Monte Carlo technique.
The main conceptual step in the solution is a re-parameterization of CMB
lensing in terms of the lensed CMB and the "inverse lensing" potential. We
demonstrate a fast implementation on simulated data including noise and a sky
cut, that uses a further acceleration based on a very mild approximation of the
inverse lensing potential. We find that the resulting Markov Chain has short
correlation lengths and excellent convergence properties, making it promising
for application to high resolution CMB data sets of the future
DegradaciĂłn ambiental y conflictos armados : las conexiones
La seguridad ambiental es un concepto complejo que puede ser analizado desde varios enfoques. La conexiĂłn entre degradaciĂłn ambiental, escasez de recursos, poco desarrollo econĂłmico e inestabilidad polĂtica puede generar rĂĄpidamente conflictos llamados ambientales, terrorismo ecolĂłgico y guerras verdes. Sin embargo, en la mayorĂa de las investigaciones sobre degradaciĂłn ambiental y conflictos armados no se tienen en cuenta los factores desarrollo econĂłmico y rĂ©gimen polĂtico, pues se considera que los problemas ambientales pueden, por sĂ solos, conducir a situaciones conflictivas nacionales, regionales e internacionales. En este contexto, los propĂłsitos de este artĂculo son plantear las diferentes tendencias ideolĂłgicas de la seguridad ambiental, definir el contenido y las causas de los conflictos ambientales y proponer un marco analĂtico complementario que incluya las variables polĂticas y econĂłmicas como generadoras de conflictos ambientales y de conflictos armados de alta intensidad. Al final, se propone una agenda de investigaciĂłn en materia de seguridad ambiental para Colombia.Environmental security is a very complex concept that may be analyzed from multiples points of view. The connection between environmental degradation, resources scarcities, low levels of economic development and political instability can quickly lead to many types of conflicts called environmental conflicts, ecological terrorism and green wars. However, most of the researchers dealing with environmental degradation and armed conflicts donât consider important factors such as âeconomic developmentâ and âtype of political regimeâ because they hypothetically think that environmental issues can lead automatically to domestic, regional and international crisis and conflicts. The purpose of this essay is to analyze the four generations of studies about environmental security, to define the contents and the causes of environmental conflicts, and, to propose an additional analytical framework that includes political and economical factors as sources of environmental conflicts and violent disputes
Precision constrained simulation of the Local Universe
We use the formalism of constrained Gaussian random field to compute a
precise large scale simulation of the 60 Mpc/h volume of our Local Universe. We
derive the constraints from the reconstructed peculiar velocities of the 2MASS
Redshift Survey. We obtain a correlation of 0.97 between the log-density field
of the dark matter distribution of the simulation and the log-density of
observed galaxies of the Local Universe. We achieve a good comparison of the
simulated velocity field to the observed velocity field obtained from the
galaxy distances of the NBG-3k. At the end, we compare the two-point
correlation function of both the 2MRS galaxies and of the dark matter particles
of the simulation. We conclude that this method is a very promising technique
of exploring the dynamics and the particularities the Universe in our
neighbourhood.Comment: 8 pages, 5 figures, accepted by MNRA
Gouvernance et gestion des espaces hydrographiques nationaux et internationaux: Iâanalyse du cas espagnol et des conflits de lâeau dans le bassin de lâEbre
Il existe trois scĂ©narios dâinsĂ©curitĂ© environnementale en Colombie dans lesquels la relation entre lâĂ©tat des ressources naturelles en eau, pĂ©trole et biodiversitĂ© (pĂ©nurie, dĂ©gradation, surexploitation, risque dâappropriation et terrorisme Ă©cologique) et la situation des rapports de force internes et rĂ©gionaux (exacerbation des tensions interĂ©tatiques, sociĂ©tales et insĂ©curitĂ© humaine) est Ă©vidente. Ce rĂ©sultat a Ă©tĂ© dĂ©montrĂ© lors dâun projet de recherche antĂ©rieur (2002-2005) menĂ©e par lâauteur de ce document de recherche dans le cadre de la ligne de recherche en sĂ©curitĂ© rĂ©gionale et internationale du Centre dâEtudes Politiques et Internationales -CEPI- des FacultĂ©s de Science Politique et Gouvernements et de Relations Internationales de lâUniversitĂ© du Rosario de Bogota..
Lagrangian reconstruction of cosmic velocity fields
We discuss a Lagrangian reconstruction method of the velocity field from
galaxy redshift catalog that takes its root in the Euler equation. This results
in a ``functional'' of the velocity field which must be minimized. This is
helped by an algorithm solving the minimization of cost-flow problems. The
results obtained by applying this method to cosmological problems are shown and
boundary effects happening in real observational cases are then discussed.
Finally, a statistical model of the errors made by the reconstruction method is
proposed.Comment: 5 pages, 5 figures, contribution to the conference "Euler's
Equations: 250 Years On" (see http://www.obs-nice.fr/etc7/EE250/); to be
published in a special issue of Physica D containing the proceedings of that
conferenc
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