214 research outputs found
A reassessment of the evidence of the Integrated Sachs-Wolfe effect through the WMAP-NVSS correlation
We reassess the estimate of the cross-correlation of the spatial distribution
of the NRAO VLA Sky Survey (NVSS) radio sources with that of Cosmic Microwave
Background (CMB) anisotropies from the Wilkinson Microwave Anisotropy Probe
(WMAP). This re-analysis is motivated by the fact that most previous studies
adopted a redshift distribution of NVSS sources inconsistent with recent data.
We find that the constraints on the bias-weighted redshift distribution,
b(z)xN(z), of NVSS sources, set by the observed angular correlation function,
w(theta), strongly mitigate the effect of the choice of N(z). If such
constraints are met, even highly discrepant redshift distributions yield
NVSS-WMAP cross-correlation functions consistent with each other within
statistical errors. The models favoured by recent data imply a bias factor,
b(z), decreasing with increasing z, rather than constant, as assumed by most
previous analyses. As a consequence, the function b(z)xN(z) has more weight at
z<1, i.e. in the redshift range yielding the maximum contribution to the ISW in
a standard LambdaCDM cosmology. On the whole, the NVSS turns out to be better
suited for ISW studies than generally believed, even in the absence of an
observational determination of the redshift distribution. The NVSS-WMAP
cross-correlation function is found to be fully consistent with the prediction
of the standard LambdaCDM cosmology.Comment: 6 pages, 2 figures, submitted to MNRA
Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity
We extend previous analyses of wide-angle correlations in the galaxy power
spectrum in redshift space to include all general relativistic effects. These
general relativistic corrections to the standard approach become important on
large scales and at high redshifts, and they lead to new terms in the
wide-angle correlations. We show that in principle the new terms can produce
corrections of nearly 10 % on Gpc scales over the usual Newtonian
approximation. General relativistic corrections will be important for future
large-volume surveys such as SKA and Euclid, although the problem of cosmic
variance will present a challenge in observing this.Comment: 14 pages, 5 figures; Typo in equation 5 corrected; results unaffecte
Interpreting large-scale redshift-space distortion measurements
The simplest theory describing large-scale redshift-space distortions (RSD),
based on linear theory and distant galaxies, depends on the growth of
cosmological structure, suggesting that strong tests of General Relativity can
be constructed from galaxy surveys. As data sets become larger and the expected
constraints more precise, the extent to which the RSD follow the simple theory
needs to be assessed in order that we do not introduce systematic errors into
the tests by introducing inaccurate simplifying assumptions. We study the
impact of the sample geometry, non-linear processes, and biases induced by our
lack of understanding of the radial galaxy distribution on RSD measurements.
Using LasDamas simulations of the Sloan Digital Sky Survey II (SDSS-II)
Luminous Red Galaxy (LRG) data, these effects are shown to be important at the
level of 20 per cent. Including them, we can accurately model the recovered
clustering in these mock catalogues on scales 30 -- 200 Mpc/h. Applying this
analysis to robustly measure parameters describing the growth history of the
Universe from the SDSS-II data, gives
and
when no prior is imposed on the
growth-rate, and the background geometry is assumed to follow a CDM
model with the WMAP + SNIa priors. The standard WMAP constrained CDM
model with General Relativity predicts
and
, which is fully consistent with
these measurements.Comment: 20 pages, 17 figures, 1 tabl
Clustering of photometric luminous red galaxies I : Growth of Structure and Baryon Acoustic Feature
The possibility of measuring redshift space (RSD) distortions using
photometric data have been recently highlighted. This effect complements and
significantly alters the detectability of baryon acoustic oscillations (BAO) in
photometric surveys. In this paper we present measurements of the angular
correlation function of luminous red galaxies (LRGs) in the photometric catalog
of the final data release (DR7) of the Sloan Digital Sky Survey II (SDSS). The
sample compromise ~ 1.5 x 10^6 LRGs distributed in 0.45 < z < 0.65, with a
characteristic photometric error of ~ 0.05. Our measured correlation centered
at z=0.55 is in very good agreement with predictions from standard LCDM in a
broad range of angular scales, . We find that the
growth of structure can indeed be robustly measured, with errors matching
expectations. The velocity growth rate is recovered as when no prior is imposed on the growth factor and the background geometry
follows a LCDM model with WMAP7+SNIa priors. This is compatible with the
corresponding General Relativity (GR) prediction for our
fiducial cosmology. If we adopt a parametrization such that , with in GR, and combine our
measurement with the corresponding ones from spectroscopic LRGs at lower
redshifts we obtain . In addition we find evidence for
the presence of the baryon acoustic feature matching the amplitude, location
and shape of LCDM predictions. The photometric BAO feature is detected with 98
% confidence level at z=0.55.Comment: 16 pages, 19 figures, minor changes to text to match accepted version
by MNRA
POPs in the Lagoon of Venice budgets and pathways.
Dioxins and furans (PCDD/Fs), polychlorobiphenyls (PCBs) and hexachlorobenzene (HCB) in the ecosystem of the Lagoon of Venice were studied, in order to provide a general picture of conditions in the Lagoon in terms of contamination by persistent organic pollutants (POPs). We present here novel data on atmospheric deposition, water, sediment and clam samples collected in the Lagoon during the period January 2001-December 2004. Atmospheric deposition was sampled monthly at six sites located both close and far from large industrial and urban sources. Water samples were collected monthly from fifteen stations, and twenty-five samples of sediments and clams (Tapes philippinarum) were collected in four areas where clams are farmed and harvested inside the Lagoon. All samples were analysed for PCDD/Fs, PCBs and HCB by HRGC/HRMS in the same laboratory. All samples examined (atmospheric deposition and water) substantially confirmed the spatial pattern reported in previously published data on sediments and atmospheric deposition: the zone surrounding the Porto Marghera petrochemical plant always had the highest levels of POPs (i.e., PCDD/Fs: atmosphere ∼6 pg of 2,3,7,8-TCDD equivalents (I-TE) m -2 d -1 ; water 0.37 pg I-TE l -1 ; sediment: 300 ng kg -1 ; clam 2.8 pg I-TE g -1 ), and the minima were found at points on the margins of the Lagoon (PCDD/Fs: atmosphere ∼ 1 pg I-TE m -2 d -1 ; water 0.05 pg I-TE l -1 ; sediment: ∼5 ng kg -1 ; clam ∼0.2 pg I-TE g -1 ). Intermediate values were often encountered in the historical city centre of Venice and in the central part of the Lagoon. To confirm this, new data on correlation between levels of PCDD/F in sediments and clams are reported, both for absolute values and for the PCDD/F “fingerprint”. There is always a clear fingerprinting signature (PCDF/PCDD>1) for samples collected near Porto Marghera, and the opposite (PCDF/PCDD<1) in the rest of the Lagoon
The BOOMERANG North America Instrument: a balloon-borne bolometric radiometer optimized for measurements of cosmic background radiation anisotropies from 0.3 to 4 degrees
We describe the BOOMERANG North America (BNA) instrument, a balloon-borne
bolometric radiometer designed to map the Cosmic Microwave Background (CMB)
radiation with 0.3 deg resolution over a significant portion of the sky. This
receiver employs new technologies in bolometers, readout electronics,
millimeter-wave optics and filters, cryogenics, scan and attitude
reconstruction. All these subsystems are described in detail in this paper. The
system has been fully calibrated in flight using a variety of techniques which
are described and compared. It has been able to obtain a measurement of the
first peak in the CMB angular power spectrum in a single balloon flight, few
hours long, and was a prototype of the BOOMERANG Long Duration Balloon (BLDB)
experiment.Comment: 40 pages, 22 figures, submitted to Ap
Cosmology from HI galaxy surveys with the SKA
The Square Kilometer Array (SKA) has the potential to produce galaxy redshift surveys which will be competitive with other state of the art cosmological experiments in the next decade. In this chapter we summarise what capabilities the first and the second phases of the SKA will be able to achieve in its current state of design. We summarise the different cosmological experiments which are outlined in further detail in other chapters of this Science Book. The SKA will be able to produce competitive Baryonic Oscillation (BAOs) measurements in both its phases. The first phase of the SKA will provide similar measurements as optical and IR experiments with completely different systematic effects whereas the second phase being transformational in terms of its statistical power. The SKA will produce very accurate Redshift Space Distortions (RSD) measurements, being superior to other experiments at lower redshifts, due to the large number of galaxies. Cross correlations of the galaxy redshift data from the SKA with radio continuum surveys and optical surveys will provide extremely good calibration of photometric redshifts as well as extremely good bounds on modifications of gravity. Basing on a Principle Component Analysis (PCA) approach, we find that the SKA will be able to provide competitive constraints on dark energy and modified gravity models. Due to the large area covered the SKA it will be a transformational experiment in measuring physics from the largest scales such as non-Gaussian signals from . Finally, the SKA might produce the first real time measurement of the redshift drift. The SKA will be a transformational machine for cosmology as it grows from an early Phase 1 to its full power
A new approach to cosmological perturbations in f(R) models
We propose an analytic procedure that allows to determine quantitatively the
deviation in the behavior of cosmological perturbations between a given f(R)
modified gravity model and a LCDM reference model. Our method allows to study
structure formation in these models from the largest scales, of the order of
the Hubble horizon, down to scales deeply inside the Hubble radius, without
employing the so-called "quasi-static" approximation. Although we restrict our
analysis here to linear perturbations, our technique is completely general and
can be extended to any perturbative order.Comment: 21 pages, 2 figures; Revised version according to reviewer's
suggestions; Typos corrected; Added Reference
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