34 research outputs found
Testing for w<-1 in the Solar System
In scalar-tensor theories of gravity, the equation of state of dark energy,
w, can become smaller than -1 without violating any energy condition. The value
of w today is tied to the level of deviations from general relativity which, in
turn, is constrained by solar system and pulsars timing experiments. The
conditions on these local constraints for w to be significantly less than -1
are established. It is demonstrated that this requires to consider theories
that differ from the Jordan-Fierz-Brans-Dicke theory and that involve either a
steep coupling function or a steep potential. It is also shown how a robust
measurement of w could probe scalar-tensor theories.Comment: 4 pages, 1 figur
Weak Lensing of Baryon Acoustic Oscillations
Baryon Acoustic Oscillations (BAO) have recently been observed in the
distribution of distant galaxies. The height and location of the BAO peak are
strong discriminators of cosmological parameters. Here we consider the ways in
which weak gravitational lensing distorts the BAO signal. We find two effects
that can affect the height of the BAO peak in the correlation function at the
percent level but that do not significantly impact the position of the peak and
the measurement of the sound horizon. BAO turn out to be robust cosmological
standard rulers.Comment: 10 pages, 4 figure
Stochastic bias of colour-selected BAO tracers by joint clustering-weak lensing analysis
The baryon acoustic oscillation (BAO) feature in the two-point correlation
function of galaxies supplies a standard ruler to probe the expansion history
of the Universe. We study here several galaxy selection schemes, aiming at
building an emission-line galaxy (ELG) sample in the redshift range
, that would be suitable for future BAO studies, providing a highly
biased galaxy sample. We analyse the angular galaxy clustering of galaxy
selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this
analysis with a halo occupation distribution (HOD) model to derive the
properties of the haloes these galaxies inhabit, in particular the galaxy bias
on large scales. We also perform a weak lensing analysis (aperture statistics)
to extract the galaxy bias and the cross-correlation coefficient and compare to
the HOD prediction.
We apply this analysis on a data set composed of the photometry of the deep
co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg), of
Canda-France-Hawai Telescope/Stripe 82 deep \emph{i}-band weak lensing survey
and of the {\it Wide-Field Infrared Survey Explorer}infrared photometric band
W1.
The analysis on the SDSS-III/constant mass galaxies selection at is
in agreement with previous studies on the tracer, moreover we measure its
cross-correlation coefficient . For the higher redshift bins, we
confirm the trends that the brightest galaxy populations selected are strongly
biased (), but we are limited by current data sets depth to derive
precise values of the galaxy bias. A survey using such tracers of the mass
field will guarantee a high significance detection of the BAO.Comment: 17 pages, 15 figures, submitted to MNRA
Weak lensing in scalar-tensor theories of gravity
This article investigates the signatures of various models of dark energy on
weak gravitational lensing, including the complementarity of the linear and
non-linear regimes. It investigates quintessence models and their extension to
scalar-tensor gravity. The various effects induced by this simplest extension
of general relativity are discussed. It is shown that, given the constraints in
the Solar System, models such as a quadratic nonminimal coupling do not leave
any signatures that can be detected while other models, such as a runaway
dilaton, which include attraction toward general relativity can let an imprint
of about 10%.Comment: 25 pages, 29 figure
Tidal virialization of dark matter haloes with clustering dark energy
International audienceWe extend the analysis of Pace et al. 1 by considering the virialization process in the extended spherical collapse model for clustering dark-energy models, i.e., accounting for dark-energy fluctuations. Differently from the standard approach, here virialization is naturally achieved by properly modelling deviations from sphericity due to shear and rotation induced by tidal interactions. We investigate the time evolution of the virial overdensity Δ in seven clustering dynamical dark energy models and compare the results to the ΛCDM model and to the corresponding smooth dark-energy models. Taking into account all the appropriate corrections, we deduce the abundance of convergence peaks for Rubin Observatory-LSST and Euclid-like weak-lensing surveys, of Sunyaev-Zel'dovich peaks for a Simon Observatory-like CMB survey, and of X-ray peaks for an eROSITA-like survey. Despite the tiny differences in Δ between clustering and smooth dark-energy models, owing to the large volumes covered by these surveys, five out of seven clustering dark-energy models can be statistically distinguished from ΛCDM. The contribution of dark-energy fluctuation cannot be neglected, especially for the Chevallier-Polarski-Limber and Albrecht-Skordis models, provided the instrumental configurations provide high signal-to-noise ratio. These results are almost independent of the tidal virialization model
The H i–halo mass relation at redshift z ∼ 1 from the Minkowski functionals of 21-cm intensity maps
International audienceThe mean and the scatter of the H i content of a dark matter halo as a function of the halo mass are useful statistics that can be used to test models of structure and galaxy formation. We investigate the possibility of constraining this H i–halo mass relation (HIHMR) from intensity maps of the redshifted 21-cm line. In particular, we use the geometry and topology of the brightness-temperature isocontours in a single frequency channel as quantified by the Minkowski functionals. First, we generate mock maps from a large N-body simulation considering the impact of thermal noise and foreground removal. We then use the Fisher information formalism to forecast constraints on a parametric model for the HIHMR. We consider a 20  000 deg^2 survey (originally proposed for dark energy science) conducted with the Square Kilometre Array Phase 1 (SKA-1) MID observatory operating in single-dish mode. For a channel bandwidth of 2 MHz, we show that an integration time of a few|| s per pointing is sufficient to image the smoothed H i distribution at redshift z ≃ 1 and to measure the HIHMR in a nearly optimal way from the Minkowski functionals. Tighter constraints on some of the parameters can be obtained by using also an independent measurement of the mean H i density. Combining the results from different frequency channels provides exquisite constraints on the evolution of the HIHMR, especially in the central frequency range of the data cube
Morphology of dark matter haloes beyond triaxiality
The morphology of haloes inform about both cosmological and galaxy formation models. We use the Minkowski Functionals (MFs) to characterize the actual morphology of haloes, only partially captured by smooth density profile, going beyond the spherical or ellipsoidal symmetry. We employ semi-analytical haloes with NFW and -profile and spherical or ellipsoidal shape to obtain a clear interpretation of MFs as function of inner and outer slope, concentration and sphericity parameters. We use the same models to mimic the density profile of -body haloes, showing that their MFs clearly differ as sensitive to internal substructures. This highlights the benefit of MFs at the halo scales as promising statistics to improve the spatial modeling of dark matter, crucial for future lensing, Sunyaev-Zel'dovich, and X-ray mass maps as well as dark matter detection based on high-accuracy data