284 research outputs found
Exploiting the full potential of photometric quasar surveys: Optimal power spectra through blind mitigation of systematics
We present optimal measurements of the angular power spectrum of the XDQSOz
catalogue of photometric quasars from the Sloan Digital Sky Survey. These
measurements rely on a quadratic maximum likelihood estimator that
simultaneously measures the auto- and cross-power spectra of four redshift
samples, and provides minimum-variance, unbiased estimates even at the largest
angular scales. Since photometric quasars are known to be strongly affected by
systematics such as spatially-varying depth and stellar contamination, we
introduce a new framework of extended mode projection to robustly mitigate the
impact of systematics on the power spectrum measurements. This technique
involves constructing template maps of potential systematics, decorrelating
them on the sky, and projecting out modes which are significantly correlated
with the data. Our method is able to simultaneously process several thousands
of nonlinearly-correlated systematics, and mode projection is performed in a
blind fashion. Using our final power spectrum measurements, we find a good
agreement with theoretical predictions, and no evidence for further
contamination by systematics. Extended mode projection not only obviates the
need for aggressive sky and quality cuts, but also provides control over the
level of systematics in the measurements, enabling the search for small signals
of new physics while avoiding confirmation bias.Comment: 13 pages, 8 figures. v2: version accepted by MNRAS. v3: systematics
templates publicly available on www.earlyuniverse.org/code, no change to
pape
No new cosmological concordance with massive sterile neutrinos
It has been claimed recently that massive sterile neutrinos could bring about
a new concordance between observations of the cosmic microwave background
(CMB), the large-scale structure (LSS) of the Universe, and local measurements
of the Hubble constant, . We demonstrate that this apparent concordance
results from combining datasets which are in significant tension, even within
this extended model, possibly indicating remaining systematic biases in the
measurements. We further show that this tension remains when the cosmological
model is further extended to include significant tensor modes, as suggested by
the recent BICEP2 results. Using the Bayesian evidence, we show that the
minimal CDM model is strongly favoured over its neutrino extensions by
various combinations of datasets. Robust data combinations yield stringent
limits of eV and eV at CL for the sum of active and sterile neutrinos,
respectively.Comment: 6 pages, version accepted by PR
Hierarchical Bayesian inference of galaxy redshift distributions from photometric surveys
Accurately characterizing the redshift distributions of galaxies is essential
for analysing deep photometric surveys and testing cosmological models. We
present a technique to simultaneously infer redshift distributions and
individual redshifts from photometric galaxy catalogues. Our model constructs a
piecewise constant representation (effectively a histogram) of the distribution
of galaxy types and redshifts, the parameters of which are efficiently inferred
from noisy photometric flux measurements. This approach can be seen as a
generalization of template-fitting photometric redshift methods and relies on a
library of spectral templates to relate the photometric fluxes of individual
galaxies to their redshifts. We illustrate this technique on simulated galaxy
survey data, and demonstrate that it delivers correct posterior distributions
on the underlying type and redshift distributions, as well as on the individual
types and redshifts of galaxies. We show that even with uninformative priors,
large photometric errors and parameter degeneracies, the redshift and type
distributions can be recovered robustly thanks to the hierarchical nature of
the model, which is not possible with common photometric redshift estimation
techniques. As a result, redshift uncertainties can be fully propagated in
cosmological analyses for the first time, fulfilling an essential requirement
for the current and future generations of surveys.Comment: 10 pages, matches version accepted in MNRAS, including new appendix
describing the effect of Bayesian shrinkage in a simplified settin
S2LET: A code to perform fast wavelet analysis on the sphere
We describe S2LET, a fast and robust implementation of the scale-discretised
wavelet transform on the sphere. Wavelets are constructed through a tiling of
the harmonic line and can be used to probe spatially localised, scale-depended
features of signals on the sphere. The scale-discretised wavelet transform was
developed previously and reduces to the needlet transform in the axisymmetric
case. The reconstruction of a signal from its wavelets coefficients is made
exact here through the use of a sampling theorem on the sphere. Moreover, a
multiresolution algorithm is presented to capture all information of each
wavelet scale in the minimal number of samples on the sphere. In addition S2LET
supports the HEALPix pixelisation scheme, in which case the transform is not
exact but nevertheless achieves good numerical accuracy. The core routines of
S2LET are written in C and have interfaces in Matlab, IDL and Java. Real
signals can be written to and read from FITS files and plotted as Mollweide
projections. The S2LET code is made publicly available, is extensively
documented, and ships with several examples in the four languages supported. At
present the code is restricted to axisymmetric wavelets but will be extended to
directional, steerable wavelets in a future release.Comment: 8 pages, 6 figures, version accepted for publication in A&A. Code is
publicly available from http://www.s2let.or
3D weak lensing with spin wavelets on the ball
We construct the spin flaglet transform, a wavelet transform to analyze spin
signals in three dimensions. Spin flaglets can probe signal content localized
simultaneously in space and frequency and, moreover, are separable so that
their angular and radial properties can be controlled independently. They are
particularly suited to analyzing of cosmological observations such as the weak
gravitational lensing of galaxies. Such observations have a unique 3D
geometrical setting since they are natively made on the sky, have spin angular
symmetries, and are extended in the radial direction by additional distance or
redshift information. Flaglets are constructed in the harmonic space defined by
the Fourier-Laguerre transform, previously defined for scalar functions and
extended here to signals with spin symmetries. Thanks to various sampling
theorems, both the Fourier-Laguerre and flaglet transforms are theoretically
exact when applied to bandlimited signals. In other words, in numerical
computations the only loss of information is due to the finite representation
of floating point numbers. We develop a 3D framework relating the weak lensing
power spectrum to covariances of flaglet coefficients. We suggest that the
resulting novel flaglet weak lensing estimator offers a powerful alternative to
common 2D and 3D approaches to accurately capture cosmological information.
While standard weak lensing analyses focus on either real or harmonic space
representations (i.e., correlation functions or Fourier-Bessel power spectra,
respectively), a wavelet approach inherits the advantages of both techniques,
where both complicated sky coverage and uncertainties associated with the
physical modeling of small scales can be handled effectively. Our codes to
compute the Fourier-Laguerre and flaglet transforms are made publicly
available.Comment: 24 pages, 4 figures, version accepted for publication in PR
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