74 research outputs found
Using correlations between CMB lensing and large-scale structure to measure primordial non-Gaussianity
We apply a new method to measure primordial non-Gaussianity, using the
cross-correlation between galaxy surveys and the CMB lensing signal to measure
galaxy bias on very large scales, where local-type primordial non-Gaussianity
predicts a divergence. We use the CMB lensing map recently published by
the Planck collaboration, and measure its external correlations with a suite of
six galaxy catalogues spanning a broad redshift range. We then consistently
combine correlation functions to extend the recent analysis by Giannantonio et
al. (2013), where the density-density and the density-CMB temperature
correlations were used. Due to the intrinsic noise of the Planck lensing map,
which affects the largest scales most severely, we find that the constraints on
the galaxy bias are similar to the constraints from density-CMB temperature
correlations. Including lensing constraints only improves the previous
statistical measurement errors marginally, and we obtain (1) from the combined data set. However, the lensing
measurements serve as an excellent test of systematic errors: we now have three
methods to measure the large-scale, scale-dependent bias from a galaxy survey:
auto-correlation, and cross-correlation with both CMB temperature and lensing.
As the publicly available Planck lensing maps have had their largest-scale
modes at multipoles removed, which are the most sensitive to the
scale-dependent bias, we consider mock CMB lensing data covering all
multipoles. We find that, while the effect of indeed
increases significantly on the largest scales, so do the contributions of both
cosmic variance and the intrinsic lensing noise, so that the improvement is
small.Comment: 5 pages, 3 figures. Additional references added. Submitted to MNRA
Constraints on primordial isocurvature perturbations and spatial curvature by Bayesian model selection
We present posterior likelihoods and Bayesian model selection analysis for
generalized cosmological models where the primordial perturbations include
correlated adiabatic and cold dark matter isocurvature components. We perform
nested sampling with flat and, for the first time, curved spatial geometries of
the Universe, using data from the cosmic microwave background (CMB)
anisotropies, the Union supernovae (SN) sample and a combined measurement of
the integrated Sachs-Wolfe (ISW) effect. The CMB alone favors a 3% (positively
correlated) isocurvature contribution in both the flat and curved cases. The
non-adiabatic contribution to the observed CMB temperature variance is 0 <
alpha_T < 7% at 98% CL in the curved case. In the flat case, combining the CMB
with SN data artificially biases the result towards the pure adiabatic LCDM
concordance model, whereas in the curved case the favored level of
non-adiabaticity stays at 3% level with all combinations of data. However, the
ratio of Bayes factors, or Delta ln(evidence), is more than 5 points in favor
of the flat adiabatic LCDM model, which suggests that the inclusion of the 5
extra parameters of the curved isocurvature model is not supported by the
current data. The results are very sensitive to the second and third acoustic
peak regions in the CMB temperature angular power: therefore a careful
calibration of these data will be required before drawing decisive conclusions
on the nature of primordial perturbations. Finally, we point out that the odds
for the flat non-adiabatic model are 1:3 compared to the curved adiabatic
model. This may suggest that it is not much less motivated to extend the
concordance model with 4 isocurvature degrees of freedom than it is to study
the spatially curved adiabatic model.Comment: 15 pages, 5 figures. V2: References and future predictions added;
accepted by PR
Constraining dark sector perturbations II: ISW and CMB lensing tomography
Any Dark Energy (DE) or Modified Gravity (MG) model that deviates from a
cosmological constant requires a consistent treatment of its perturbations,
which can be described in terms of an effective entropy perturbation and an
anisotropic stress. We have considered a recently proposed generic
parameterisation of DE/MG perturbations and compared it to data from the Planck
satellite and six galaxy catalogues, including temperature-galaxy (Tg), CMB
lensing-galaxy and galaxy-galaxy (gg) correlations. Combining these observables
of structure formation with tests of the background expansion allows us to
investigate the properties of DE/MG both at the background and the perturbative
level. Our constraints on DE/MG are mostly in agreement with the cosmological
constant paradigm, while we also find that the constraint on the equation of
state w (assumed to be constant) depends on the model assumed for the
perturbation evolution. We obtain (95% CL; CMB+gg+Tg)
in the entropy perturbation scenario; in the anisotropic stress case the result
is . Including the lensing correlations shifts the
results towards higher values of w. If we include a prior on the expansion
history from recent Baryon Acoustic Oscillations (BAO) measurements, we find
that the constraints tighten closely around , making it impossible to
measure any DE/MG perturbation evolution parameters. If, however, upcoming
observations from surveys like DES, Euclid or LSST show indications for a
deviation from a cosmological constant, our formalism will be a useful tool
towards model selection in the dark sector.Comment: 25 pages, 8 figures; minor update for consistency with version
accepted by JCAP (13/01/2015
Chaplygin gas in light of recent Integrated Sachs--Wolfe effect data
We investigate the possibility of constraining Chaplygin dark energy models
with current Integrated Sachs Wolfe effect data. In the case of a flat universe
we found that generalized Chaplygin gas models must have an energy density such
that and an equation of state at 95% c.l.. We also
investigate the recently proposed Silent Chaplygin models, constraining
and at 95% c.l.. Better measurements of the CMB-LSS
correlation will be possible with the next generation of deep redshift surveys.
This will provide independent and complementary constraints on unified dark
energy models such as the Chaplygin gas.Comment: 5 pages, 4 figure
Combining clustering and abundances of galaxy clusters to test cosmology and primordial non-Gaussianity
We present the clustering of galaxy clusters as a useful addition to the
common set of cosmological observables. The clustering of clusters probes the
large-scale structure of the Universe, extending galaxy clustering analysis to
the high-peak, high-bias regime. Clustering of galaxy clusters complements the
traditional cluster number counts and observable-mass relation analyses,
significantly improving their constraining power by breaking existing
calibration degeneracies. We use the maxBCG galaxy clusters catalogue to
constrain cosmological parameters and cross-calibrate the mass-observable
relation, using cluster abundances in richness bins and weak-lensing mass
estimates. We then add the redshift-space power spectrum of the sample,
including an effective modelling of the weakly non-linear contribution and
allowing for an arbitrary photometric redshift smoothing. The inclusion of the
power spectrum data allows for an improved self-calibration of the scaling
relation. We find that the inclusion of the power spectrum typically brings a
per cent improvement in the errors on the fluctuation amplitude
and the matter density . Finally, we apply this
method to constrain models of the early universe through the amount of
primordial non-Gaussianity of the local type, using both the variation in the
halo mass function and the variation in the cluster bias. We find a constraint
on the amount of skewness () from the
cluster data alone.Comment: 12 pages, 10 figures, 2 tables. Minor changes to match published
version on MNRA
Detectability of a phantom-like braneworld model with the integrated Sachs-Wolfe effect
We study a braneworld model in which a phantom-like behaviour occurs with
only cold dark matter and a cosmological constant, due to a large distance
modification of gravity. With the addition of curvature, the geometrical tests
are not strict enough to rule out models in which gravity is modified
significantly on large scales. We show that this degeneracy in the parameter
space is broken by the structure formation tests, such as the integrated
Sachs-Wolfe effect, which can probe general relativity on large scales.Comment: 7 pages, 4 figure
Structure formation from non-Gaussian initial conditions: multivariate biasing, statistics, and comparison with N-body simulations
We study structure formation in the presence of primordial non-Gaussianity of
the local type with parameters f_NL and g_NL. We show that the distribution of
dark-matter halos is naturally described by a multivariate bias scheme where
the halo overdensity depends not only on the underlying matter density
fluctuation delta, but also on the Gaussian part of the primordial
gravitational potential phi. This corresponds to a non-local bias scheme in
terms of delta only. We derive the coefficients of the bias expansion as a
function of the halo mass by applying the peak-background split to common
parametrizations for the halo mass function in the non-Gaussian scenario. We
then compute the halo power spectrum and halo-matter cross spectrum in the
framework of Eulerian perturbation theory up to third order. Comparing our
results against N-body simulations, we find that our model accurately describes
the numerical data for wavenumbers k < 0.1-0.3 h/Mpc depending on redshift and
halo mass. In our multivariate approach, perturbations in the halo counts trace
phi on large scales and this explains why the halo and matter power spectra
show different asymptotic trends for k -> 0. This strongly scale-dependent bias
originates from terms at leading order in our expansion. This is different from
what happens using the standard univariate local bias where the scale-dependent
terms come from badly behaved higher-order corrections. On the other hand, our
biasing scheme reduces to the usual local bias on smaller scales where |phi| is
typically much smaller than the density perturbations. We finally discuss the
halo bispectrum in the context of multivariate biasing and show that, due to
its strong scale and shape dependence, it is a powerful tool for the detection
of primordial non-Gaussianity from future galaxy surveys.Comment: 26 pages, 16 figures. Minor modifications, version accepted by Phys.
Rev.
- …