353 research outputs found
On the use of bianisotropic huygens' metasurfaces to build leaky-wave antennas
The Electromagnetics AcademyHuygens' metasurfaces are considered a powerful tool to achieve anomalous electromagnetic field transformations. They consist of an artifcial surface built of pairs of collocated electric and magetic dipoles that force the boundary conditions for the desired transformation to be ful lled [1]. Despite their possibilities, the achievable transformations must ful l some conditions. In [2] it was
shown that Huygens' metasurfaces with passive and lossless particles can achieve an arbitrary field transformation provided that the power is conserved at each point of the metasurface and there is wave impedance matching. However, it was shown in [3], that by introducing bianisotropy of the omega-type, the matching condition can be suppressed, which allows the control of both the transmission and rejection coe cients on the metasurface.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
Position-dependent correlation function from the SDSS-III Baryon Oscillation Spectroscopic Survey Data Release 10 CMASS Sample
We report on the first measurement of the three-point function with the
position-dependent correlation function from the SDSS-III Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 10 CMASS sample. This new observable
measures the correlation between two-point functions of galaxy pairs within
different subvolumes, , where is the
location of a subvolume, and the corresponding mean overdensities,
. This correlation, which we call the "integrated
three-point function", , measures a three-point function of two
short- and one long-wavelength modes, and is generated by nonlinear
gravitational evolution and possibly also by the physics of inflation. The
measured from the BOSS data lies within the scatter of those from
the mock galaxy catalogs in redshift space, yielding a ten-percent-level
determination of the amplitude of . The tree-level perturbation
theory in redshift space predicts how this amplitude depends on the linear and
quadratic nonlinear galaxy bias parameters ( and ), as well as on the
amplitude and linear growth rate of matter fluctuations ( and ).
Combining with the constraints on and
from the global two-point correlation function and that on from the
weak lensing signal of BOSS galaxies, we measure (68% C.L.)
assuming standard perturbation theory at the tree level and the local bias
model.Comment: 30 pages, 11 figures. revised version submitted to JCA
Gaussian covariance matrices for anisotropic galaxy clustering measurements
Measurements of the redshift-space galaxy clustering have been a prolific
source of cosmological information in recent years. Accurate covariance
estimates are an essential step for the validation of galaxy clustering models
of the redshift-space two-point statistics. Usually, only a limited set of
accurate N-body simulations is available. Thus, assessing the data covariance
is not possible or only leads to a noisy estimate. Further, relying on
simulated realisations of the survey data means that tests of the cosmology
dependence of the covariance are expensive. With these points in mind, this
work presents a simple theoretical model for the linear covariance of
anisotropic galaxy clustering observations with synthetic catalogues.
Considering the Legendre moments (`multipoles') of the two-point statistics and
projections into wide bins of the line-of-sight parameter (`clustering
wedges'), we describe the modelling of the covariance for these anisotropic
clustering measurements for galaxy samples with a trivial geometry in the case
of a Gaussian approximation of the clustering likelihood. As main result of
this paper, we give the explicit formulae for Fourier and configuration space
covariance matrices. To validate our model, we create synthetic HOD galaxy
catalogues by populating the haloes of an ensemble of large-volume N-body
simulations. Using linear and non-linear input power spectra, we find very good
agreement between the model predictions and the measurements on the synthetic
catalogues in the quasi-linear regime.Comment: 17 pages, 16 figures, 3 tables; modified to match version accepted by
MNRA
Toward a robust inference method for the galaxy bispectrum: likelihood function and model selection
The forthcoming generation of galaxy redshift surveys will sample the
large-scale structure of the Universe over unprecedented volumes with
high-density tracers. This advancement will make robust measurements of
three-point clustering statistics possible. In preparation for this
improvement, we investigate how several methodological choices can influence
inferences based on the bispectrum about galaxy bias and shot noise. We first
measure the real-space bispectrum of dark-matter haloes extracted from 298
N-body simulations covering a volume of approximately . We then fit a series of theoretical models based on tree-level
perturbation theory to the numerical data. To achieve this, we estimate the
covariance matrix of the measurement errors by using 10,000 mock catalogues
generated with the Pinocchio code. We study how the model constraints are
influenced by the binning strategy for the bispectrum configurations and by the
form of the likelihood function. We also use Bayesian model-selection
techniques to single out the optimal theoretical description of our data. We
find that a three-parameter bias model combined with Poissonian shot noise is
necessary to model the halo bispectrum up to scales of , although fitting formulae that relate the bias
parameters can be helpful to reduce the freedom of the model without
compromising accuracy. Our data clearly disfavour local Eulerian and local
Lagrangian bias models and do not require corrections to Poissonian shot noise.
We anticipate that model-selection diagnostics will be particularly useful to
extend the analysis to smaller scales as, in this case, the number of model
parameters will grow significantly large.Comment: 38 pages, 17 figures; major revisions: inclusion of open triangle
bins in all results, new priors for the shot-noise parameters, and additional
comparison with Gaussian varianc
Testing one-loop galaxy bias: Cosmological constraints from the power spectrum
We investigate the impact of different assumptions in the modeling of one-loop galaxy bias on the recovery of cosmological parameters, as a follow-up of the analysis done in the first paper of the series at fixed cosmology. To carry out these tests we focus on the real-space galaxy-power spectrum from a set of three different synthetic galaxy samples whose clustering properties are meant to match the ones of the CMASS and LOWZ catalogs of BOSS and the SDSS Main Galaxy Sample. We investigate the relevance of allowing for either short range nonlocality or scale-dependent stochasticity by fitting the real-space galaxy autopower spectrum or the combination of galaxy-galaxy and galaxy-matter power spectrum. From a comparison among the goodness of fit (χ2), unbiasedness of cosmological parameters (FoB), and figure of merit (FoM) of the model, we find that a simple four-parameter model (linear, quadratic, cubic nonlocal bias, and constant shot noise) with fixed quadratic tidal bias provides a robust modeling choice for the autopower spectrum of the three galaxy samples, up to kmax ¼ 0.3h Mpc−1 and for an effective volume of 6h−3 Gpc3. Instead, a joint analysis of the two observables fails at larger scales, and a model extension with either higher derivatives or scale-dependent shot noise is necessary to reach a similar kmax, with the latter providing the most accurate and stable results. Throughout the majority of the paper, we fix the description of the nonlinear matter evolution using a hybrid perturbative-N-body approach, RESPRESSO, that was found in the first paper to be the closest performing to the measured matter spectrum. We also test the impact of different modeling assumptions based on perturbative approaches, such as galilean-invariant Renormalised Perturbation Theory (gRPT) and effective field theory (EFT). In all cases, we find the inclusion of scale-dependent shot noise to increase the range of validity of the model in terms of FoB and χ2. Interestingly, these model extensions with additional free parameters do not necessarily lead to an increase in the maximally achievable FoM for the cosmological parameters ðh; Ωch2; AsÞ, which are generally consistent with those of the simpler model at smaller kmax
The cosmic shallows I: interaction of CMB photons in extended galaxy halos
We report and analyse the presence of foregrounds in the cosmic microwave
background (CMB) radiation associated to extended galactic halos. Using the
cross correlation of Planck and WMAP maps and the 2MRS galaxy catalogue, we
find that the mean temperature radial profiles around nearby galaxies at show a statistically significant systematic decrease of
extending up to several galaxy radii. This effect strongly
depends on the galaxy morphological type at scales within several tens of times
the galaxy size, becoming nearly independent of galaxy morphology at larger
scales. The effect is significantly stronger for the more extended galaxies,
with galaxy clustering having a large impact on the results. Our findings
indicate the presence of statistically relevant foregrounds in the CMB maps
that should be considered in detailed cosmological studies. Besides, we argue
that these can be used to explore the intergalactic medium surrounding bright
late-type galaxies and allow for diverse astrophysical analyses.Comment: 10 pages, 9 figures, submitted to MNRA
COMET: Clustering Observables Modelled by Emulated perturbation Theory
In this paper we present COMET, a Gaussian process emulator of the galaxy
power spectrum multipoles in redshift-space. The model predictions are based on
one-loop perturbation theory and we consider two alternative descriptions of
redshift-space distortions: one that performs a full expansion of the real- to
redshift-space mapping, as in recent effective field theory models, and another
that preserves the non-perturbative impact of small-scale velocities by means
of an effective damping function. The outputs of COMET can be obtained at
arbitrary redshifts (up to ), for arbitrary fiducial background
cosmologies, and for a large parameter space that covers the shape parameters
, , and , as well as the evolution parameters ,
, , , and . This flexibility does not impair COMET's
accuracy, since we exploit an exact degeneracy between the evolution parameters
that allows us to train the emulator on a significantly reduced parameter
space. While the predictions are sped up by at least two orders of magnitude,
validation tests reveal an accuracy of for the monopole and
quadrupole ( for the hexadecapole), or alternatively, better than
for all three multipoles in comparison to statistical
uncertainties expected for the Euclid survey with a tenfold increase in volume.
We show that these differences translate into shifts in mean posterior values
that are at most of the same size, meaning that COMET can be used with the same
confidence as the exact underlying models. COMET is a publicly available Python
package that also provides the tree-level bispectrum multipoles in
redshift-space and Gaussian covariance matrices.Comment: 18 pages, 10 figures; for the COMET Python package, see
https://gitlab.com/aegge/comet-em
Non-fiducial cosmological test from geometrical and dynamical distortions around voids
We present a new cosmological test using the distribution of galaxies around cosmic voids without assuming a fiducial cosmology. The test is based on a physical model for the void-galaxy cross-correlation function projected along and perpendicular to the line of sight. We treat correlations in terms of void-centric angular distances and redshift differences between void-galaxy pairs, hence it is not necessary to assume a fiducial cosmology. This model reproduces the coupled dynamical (Kaiser effect, RSD) and geometrical (Alcock-Paczynski effect, GD) distortions that affect the correlation measurements. It also takes into account the scale mixing due to the projection ranges in both directions. The model is general, so it can be applied to an arbitrary cylindrical binning scheme, not only in the case of the projected correlations. It primarily depends on two cosmological parameters: Ωm, the matter fraction of the Universe today (sensitive to GD), and β, the ratio between the growth rate factor of density perturbations and the tracer bias (sensitive to RSD). In the context of the new generation of galaxy spectroscopic surveys, we calibrated the test using the Millennium XXL simulation for different redshifts. The method successfully recovers the cosmological parameters. We studied the effect of measuring with different projection ranges, finding robust results up to wide ranges. The resulting data covariance matrices are relatively small, which reduces the noise in the Gaussian likelihood analysis and will allow the usage of a smaller number of mock catalogues. The performance evaluated in this work indicates that the developed method is a promising test to be applied on real data.Fil: Correa, Carlos Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Paz, Dante Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Padilla, Nelson David. Departamento de Astronomia y Astrofisica; ChileFil: Ruiz, Andrés Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Astronomía Teórica y Experimental. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba. Instituto de Astronomía Teórica y Experimental; ArgentinaFil: Angulo, Raúl E.. Donostia International Physics Centre; EspañaFil: Sánchez, Ariel G.. Max Plank Institute For Extraterrestrial Physics; Alemani
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