550 research outputs found
Dark Energy Survey Year 1 Results: Weak Lensing Shape Catalogues
We present two galaxy shape catalogues from the Dark Energy Survey Year 1 data set, covering 1500 deg^2 with a median redshift of 0.59. The catalogues cover two main fields: Stripe 82, and an area overlapping the South Pole Telescope survey region. We describe our data analysis process and in particular our shape measurement using two independent shear measurement pipelines, METACALIBRATION and IM3SHAPE. The METACALIBRATION catalogue uses a Gaussian model with an innovative internal calibration scheme, and was applied to riz bands, yielding 34.8M objects. The IM3SHAPE catalogue uses a maximum-likelihood bulge/disc model calibrated using simulations, and was applied to r-band data, yielding 21.9M objects. Both catalogues pass a suite of null tests that demonstrate their fitness for use in weak lensing science. We estimate the 1Ď uncertainties in multiplicative shear calibration to be 0.013 and 0.025 for the METACALIBRATION and IM3SHAPE catalogues, respectively
What the small angle CMB really tells us about the curvature of the Universe
5 pages, 3 figures. Corrections made to published version5 pages, 3 figures. Corrections made to published version5 pages, 3 figures. Corrections made to published versionIt is well known that observations of the cosmic microwave background (CMB) are highly sensitive to the spatial curvature of the Universe, k. Here we find that what is in fact being tightly constrained by small angle fluctuations is spatial curvature near the surface of last scattering, and that if we allow k to be a function of position, rather than taking a constant value everywhere, then considerable spatial curvature is permissible within our own locale. This result is of interest for the giant void models that attempt to explain the supernovae observations without Dark Energy. We find voids models with a homogeneous big bang can be compatible with the observed small angle CMB, but only if they exist in a positively curved universe. To be compatible with local measurements of H_0, however, we find that a radially varying bang time is required
Vector field models of modified gravity and the dark sector
We present a comprehensive investigation of cosmological constraints on the
class of vector field formulations of modified gravity called Generalized
Einstein-Aether models. Using linear perturbation theory we generate cosmic
microwave background and large-scale structure spectra for general parameters
of the theory, and then constrain them in various ways. We investigate two
parameter regimes: a dark-matter candidate where the vector field sources
structure formation, and a dark-energy candidate where it causes late-time
acceleration. We find that the dark matter candidate does not fit the data, and
identify five physical problems that can restrict this and other theories of
dark matter. The dark energy candidate does fit the data, and we constrain its
fundamental parameters; most notably we find that the theory's kinetic index
parameter can differ significantly from its CDM
value.Comment: 16 pages, 11 figure
Constraining Lorentz violation with cosmology
The Einstein-Aether theory provides a simple, dynamical mechanism for
breaking Lorentz invariance. It does so within a generally covariant context
and may emerge from quantum effects in more fundamental theories. The theory
leads to a preferred frame and can have distinct experimental signatures. In
this letter, we perform a comprehensive study of the cosmological effects of
the Einstein-Aether theory and use observational data to constrain it. Allied
to previously determined consistency and experimental constraints, we find that
an Einstein-Aether universe can fit experimental data over a wide range of its
parameter space, but requires a specific rescaling of the other cosmological
densities.Comment: 4 pages, 4 figure
Dark Energy Survey Year 1 Results: Weak Lensing Shape Catalogues
We present two galaxy shape catalogues from the Dark Energy Survey Year 1 data set, covering 1500 deg^2 with a median redshift of 0.59. The catalogues cover two main fields: Stripe 82, and an area overlapping the South Pole Telescope survey region. We describe our data analysis process and in particular our shape measurement using two independent shear measurement pipelines, METACALIBRATION and IM3SHAPE. The METACALIBRATION catalogue uses a Gaussian model with an innovative internal calibration scheme, and was applied to riz bands, yielding 34.8M objects. The IM3SHAPE catalogue uses a maximum-likelihood bulge/disc model calibrated using simulations, and was applied to r-band data, yielding 21.9M objects. Both catalogues pass a suite of null tests that demonstrate their fitness for use in weak lensing science. We estimate the 1Ď uncertainties in multiplicative shear calibration to be 0.013 and 0.025 for the METACALIBRATION and IM3SHAPE catalogues, respectively
Weak gravitational lensing with the Square Kilometre Array
We investigate the capabilities of various stages of the SKA to perform
world-leading weak gravitational lensing surveys. We outline a way forward to
develop the tools needed for pursuing weak lensing in the radio band. We
identify the key analysis challenges and the key pathfinder experiments that
will allow us to address them in the run up to the SKA. We identify and
summarize the unique and potentially very powerful aspects of radio weak
lensing surveys, facilitated by the SKA, that can solve major challenges in the
field of weak lensing. These include the use of polarization and rotational
velocity information to control intrinsic alignments, and the new area of weak
lensing using intensity mapping experiments. We show how the SKA lensing
surveys will both complement and enhance corresponding efforts in the optical
wavebands through cross-correlation techniques and by way of extending the
reach of weak lensing to high redshift.Comment: 19 pages, 6 figures. Cosmology Chapter, Advancing Astrophysics with
the SKA (AASKA14) Conference, Giardini Naxos (Italy), June 9th-13th 201
C-Band All-Sky Survey: A First Look at the Galaxy
We present an analysis of the diffuse emission at 5 GHz in the first quadrant
of the Galactic plane using two months of preliminary intensity data taken with
the C-Band All Sky Survey (C-BASS) northern instrument at the Owens Valley
Radio Observatory, California. Combining C-BASS maps with ancillary data to
make temperature-temperature plots we find synchrotron spectral indices of
between 0.408 GHz and 5 GHz and between 1.420 GHz and 5 GHz for ,
. Through the subtraction of a radio recombination
line (RRL) free-free template we determine the synchrotron spectral index in
the Galactic plane () to be between
0.408 GHz and 5 GHz, with a contribution of per cent from free-free
emission at 5\,GHz. These results are consistent with previous low frequency
measurements in the Galactic plane. By including C-BASS data in spectral fits
we demonstrate the presence of anomalous microwave emission (AME) associated
with the HII complexes W43, W44 and W47 near 30 GHz, at 4.4 sigma, 3.1 sigma
and 2.5 sigma respectively. The CORNISH VLA 5 GHz source catalogue rules out
the possibility that the excess emission detected around 30\;GHz may be due to
ultra-compact HII regions. Diffuse AME was also identified at a 4 sigma level
within , between 5
GHz and 22.8 GHz.Comment: 16 pages, 9 figures, submitted to MNRAS, referee's corrections made,
awaiting for final approval for publicatio
MAXIPOL: Cosmic Microwave Background Polarimetry Using a Rotating Half-Wave Plate
We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure
the E-mode polarization of the cosmic microwave background radiation (CMB).
MAXIPOL is the first bolometric CMB experiment to observe the sky using rapid
polarization modulation. To build MAXIPOL, the CMB temperature anisotropy
experiment MAXIMA was retrofitted with a rotating half-wave plate and a
stationary analyzer. We describe the instrument, the observations, the
calibration and the reduction of data collected with twelve polarimeters
operating at 140 GHz and with a FWHM beam size of 10 arcmin. We present maps of
the Q and U Stokes parameters of an 8 deg^2 region of the sky near the star
Beta Ursae Minoris. The power spectra computed from these maps give weak
evidence for an EE signal. The maximum-likelihood amplitude of
l(l+1)C^{EE}_{l}/(2 pi) is 55_{-45}^{+51} uK^2 (68%), and the likelihood
function is asymmetric and skewed positive such that with a uniform prior the
probability that the amplitude is positive is 96%. This result is consistent
with the expected concordance LCDM amplitude of 14 uK^2. The maximum likelihood
amplitudes for l(l+1)C^{BB}_{l}/(2 pi) and are
-31_{-19}^{+31} and 18_{-34}^{+27} uK^2 (68%), respectively, which are
consistent with zero. All of the results are for one bin in the range 151 < l <
693. Tests revealed no residual systematic errors in the time or map domain. A
comprehensive discussion of the analysis of the data is presented in a
companion paper.Comment: 19 pages, 11 figures, 2 tables, submitted to Ap
Ambiguous Tests of General Relativity on Cosmological Scales
There are a number of approaches to testing General Relativity (GR) on linear
scales using parameterized frameworks for modifying cosmological perturbation
theory. It is sometimes assumed that the details of any given parameterization
are unimportant if one uses it as a diagnostic for deviations from GR. In this
brief report we argue that this is not necessarily so. First we show that
adopting alternative combinations of modifications to the field equations
significantly changes the constraints that one obtains. In addition, we show
that using a parameterization with insufficient freedom significantly tightens
the apparent theoretical constraints. Fundamentally we argue that it is almost
never appropriate to consider modifications to the perturbed Einstein equations
as being constraints on the effective gravitational constant, for example, in
the same sense that solar system constraints are. The only consistent
modifications are either those that grant near-total freedom, as in
decomposition methods, or ones which map directly to a particular part of
theory space
Dark energy survey year 1 results: The lensing imprint of cosmic voids on the cosmic microwave background
Cosmic voids gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint on degree scales. We use the simulated CMB lensing convergence map from the Marenostrum Institut de Ciencias de lâEspai (MICE) N-body simulation to calibrate our detection strategy for a given void definition and galaxy tracer density. We then identify cosmic voids in Dark Energy Survey (DES) Year 1 data and stack the Planck 2015 lensing convergence map on their locations, probing the consistency of simulated and observed void lensing signals. When fixing the shape of the stacked convergence profile to that calibrated from simulations, we find imprints at the 3Ď significance level for various analysis choices. The best measurement strategies based on the MICE calibration process yield S/N â 4 for DES Y1, and the best-fitting amplitude recovered from the data is consistent with expectations from MICE (A â 1). Given these results as well as the agreement between them and N-body simulations, we conclude that the previously reported excess integrated SachsâWolfe (ISW) signal associated with cosmic voids in DES Y1 has no counterpart in the Planck CMB lensing map.This work has made use of CosmoHub (see Carretero et al. 2017).
CosmoHub has been developed by the Port dâInformacio Cient ´ ´Ĺfica
(PIC), maintained through a collaboration of the Institut de F´Ĺsica
dâAltes Energies (IFAE) and the Centro de Investigaciones Energeticas, Medioambientales y Tecnol ´ ogicas (CIEMAT), and was ´
partially funded by the âPlan Estatal de Investigacion Cient ´ ´Ĺfica y
Tecnica y de Innovaci ´ onâ program of the Spanish government. ´
Funding for the DES Projects has been provided by the US Department of Energy, the US National Science Foundation, the Ministry
of Science and Education of Spain, the Science and Technology
Facilities Council of the United Kingdom, the Higher Education
Funding Council for England, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign,
the Kavli Institute of Cosmological Physics at the University of
Chicago, the Center for Cosmology and Astro-Particle Physics at the
Ohio State University, the Mitchell Institute for Fundamental Physics
and Astronomy at Texas A&M University, Financiadora de Estudos
e Projetos, Fundac¸ao Carlos Chagas Filho de Amparo Ë a Pesquisa do `
Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento
Cient´Ĺfico e Tecnologico and the Minist ´ erio da Ci ´ encia, Tecnologia Ë
e Inovac¸ao, the Deutsche Forschungsgemeinschaft, and the Collab- Ë
orating Institutions in the Dark Energy Survey.
The Collaborating Institutions are Argonne National Laboratory,
the University of California at Santa Cruz, the University of
Cambridge, Centro de Investigaciones Energeticas, Medioambien- ´
tales y Tecnologicas-Madrid, the University of Chicago, Univer- ´
sity College London, the DES-Brazil Consortium, the University
of Edinburgh, the Eidgenossische Technische Hochschule (ETH) ¨
Zurich, Fermi National Accelerator Laboratory, the University of ¨
Illinois at Urbana-Champaign, the Institut de Ciencies de lâEspai `
(IEEC/CSIC), the Institut de F´Ĺsica dâAltes Energies, Lawrence
Berkeley National Laboratory, the Ludwig-Maximilians Universitat¨
Munchen and the associated Excellence Cluster Universe, the Uni- ¨
versity of Michigan, the National Optical Astronomy Observatory,
the University of Nottingham, The Ohio State University, the
University of Pennsylvania, the University of Portsmouth, SLAC
National Accelerator Laboratory, Stanford University, the University
of Sussex, Texas A&M University, and the OzDES Membership
Consortium.
This paper is based in part on observations at Cerro Tololo InterAmerican Observatory, National Optical Astronomy Observatory,
which is operated by the Association of Universities for Research in
Astronomy (AURA) under a cooperative agreement with the National
Science Foundation.
The DES data management system is supported by the National Science Foundation under Grant Numbers AST-1138766
and AST-1536171. The DES participants from Spanish institutions are partially supported by MINECO under grants AYA2015-
71825, ESP2015-66861, FPA2015-68048, SEV-2016-0588, SEV2016-0597, and MDM-2015-0509, some of which include ERDF
funds from the European Union. IFAE is partially funded by the
CERCA program of the Generalitat de Catalunya.
Research leading to these results has received funding from the
European Research Council under the European Unionâs Seventh
Framework Program (FP7/2007-2013) including ERC grant agreements 240672, 291329, 306478, and 615929. We acknowledge
support from the Brazilian Instituto Nacional de Cienciae Tecnologia Ë
(INCT) e-Universe (CNPq grant 465376/2014-2).
This paper has been authored by Fermi Research Alliance, LLC
under Contract No. DE-AC02-07CH11359 with the US Department
of Energy, Office of Science, Office of High Energy Physics.
PV acknowledges the support from the grant MIUR PRIN 2015
âCosmology and Fundamental Physics: illuminating the Dark Universe with Euclidâ.
AK has been supported by a Juan de la Cierva fellowship from
MINECO with project number IJC2018-037730-I. Funding for this
project was also available in part through SEV-2015-0548 and
AYA2017-89891-P.
This project has also received funding from the European Unionâs
Horizon 2020 research and innovation programme under the Marie
SkĹodowska-Curie grant agreement No. 754558.Peer reviewe
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