Showing papers by "Francesca Perrotta published in 2003"

Arc Statistics in Cosmological Models with Dark Energy

Abstract: We investigate how the probability of the formation of giant arcs in galaxy clusters is expected to change in cos- mological models dominated by dark energy with an equation of state p = wρc 2 compared to cosmological-constant or open models To do so, we use a simple analytic model for arc cross sections based on the Navarro-Frenk-White density profile which we demonstrate reproduces essential features of numerically determined arc cross sections Since analytic lens models are known to be inadequate for accurate absolute quantifications of arc probabilities, we use them only for studying changes rel- ative to cosmological-constant models Our main results are (1) the order of magnitude difference between the arc probabilities in low density, spatially flat and open CDM models found numerically is reproduced by our analytic model, and (2) dark-energy cosmologies with w> −1 increase the arc optical depth by at most a factor of two and are thus unlikely to reconcile arc statistics with spatially flat cosmological models with low matter density

Predictions for statistical properties of forming spheroidal galaxies

Abstract: We show that the features of the recent astrophysically motivated model by Granato et al. are fully consistent with the available statistical measurements of galaxies at (sub)millimetre wavelengths. We quantitatively predict the impact of this scenario on near-future cosmological observations dealing with spatial and flux statistical distribution of (sub)millimetre galaxies. We show that the expected angular correlation function of spheroids is compatible with available data. We compute the expected power spectrum of fluctuations due to clustering at the frequencies of the High Frequency Instrument (HFI) on ESA's Planck satellite: the clustering signal is found to be detectable in regions of low interstellar dust emission. A further distinctive prediction of the adopted model is a remarkably high fraction of gravitationally lensed sources at bright millimetre/submillimetre fluxes. In fact, since most spheroids burn at redshift z≃ 2–3 according to the adopted model, gravitational lensing amplifies a significant number of high-z forming spheroidal galaxies, which will be detectable by large-area, shallow surveys at millimetre/submillimetre wavelengths, such as those carried out by Planck/HFI. Allowing for other source populations, we find that the fraction of gravitationally lensed millimetre/submillimetre sources at fluxes >100 mJy is expected to be up to ≃40 per cent.

Astrophysical component separation of COBE-DMR 4-yr data with FastICA

Abstract: We present an application of the fast Independent Component Analysis FastICA method to the COBE-DMR 4yr data. Although the signal-to-noise ratio in the COBE-DMR data is typically � 1, the approach is able to extract the CMB signal with high confidence when working at high galactic latitudes. However, the foreground emission components have too low a S/N ratio to be reconstructed by this method (moreover, the number of components which can be reconstructed is directly limited by the number of input channels). The reconstructed CMB map shows the expected frequency scaling of the CMB. We fit the resulting CMB component for the rms quadrupole normalisation Qrms PS and primordial spectral index n and find results in excellent agreement with those derived from the minimum-noise combination of the 90 and 53 GHz DMR channels without galactic emission correction. We extend the analysis by including additional channels (priors) such as the Haslam map of radio emission at 408 MHz and the DIRBE 140� m map of galactic infra-red emission. Subsequently, the FastICA algorithm is able to both detect galactic foreground emission and separate it from the dominant CMB signal. Fitting the resulting CMB component for Qrms PS and n we find good agreement with the

Probing dark energy with the cosmic microwave background: projected constraints from the Wilkinson Microwave Anisotropy Probe and Planck

Abstract: We investigate the accuracy attainable by forthcoming space-based observations of the cosmic microwave background (CMB) temperature and polarization anisotropy in constraining the dark energy density parameter ?Q and equation of state wQ = pQ/?Q. Despite degeneracies among parameters, it is possible for high-precision observations such as those from the Wilkinson Microwave Anisotropy Probe and Planck to provide interesting information on the nature of the dark energy. Furthermore, we show that imposing a flat universe constraint makes it possible to obtain tight limits in the space of dark energy parameters even from the CMB alone.

Probing Dark Energy with the Cosmic Microwave Background: Projected Constraints from the Wilkinson Microwave Anisotropy Probe and Planck

Abstract: We investigate the accuracy attainable by forthcoming space-based observations of the cosmic microwave background (CMB) temperature and polarization anisotropy in constraining the dark energy density parameter ?Q and equation of state wQ = pQ/?Q. Despite degeneracies among parameters, it is possible for high-precision observations such as those from the Wilkinson Microwave Anisotropy Probe and Planck to provide interesting information on the nature of the dark energy. Furthermore, we show that imposing a flat universe constraint makes it possible to obtain tight limits in the space of dark energy parameters even from the CMB alone.

Scalar field dark energy and cosmic microwave background

Abstract: A dynamical scalar field represents the simplest generalization of a pure Cosmological Constant as a candidate to explain the recent evidence in favour of the accelerated cosmic expansion. We review the dynamical properties of such a component, and argue that, even if the background expectation value of this field is fixed and the equation of state is the same as a Cosmological Constant, scalar field fluctuations can still be used to distinguish the two components. We compare predicted spectra of Cosmic Microvave Background (CMB) anisotropies in tracking scalar field cosmologies with the present CMB data, in order to get constraints on the amount and equation of state of dark energy. High precision experiments like SNAP, Planck and SNFactory , together with the data on Large Scale Structure, are needed to probe this issue with the necessary accuracy. Here we show the intriguing result that, with a strong prior on the value of the Hubble constant today, the assumption of a flat universe, and consistency relations between amplitude and spectral index of primordial gravitational waves, the present CMB data at 1σ give indication of a dark energy equation of state larger than −1, while the ordinary Cosmological Constant is recovered at 2σ.

Weak lensing, structure formation and dark energy

Abstract: We study how CMB bispectrum, produced by weak gravitational lensing and structure formation, can constrain the redshift evolution of the dark energy equation of state independently on its present value. Analyzing the line of sight contribution to the angular CMB bispectrum, we find that the relevant redshift at which the structure formation contributes to the signal is $0.1 \lsim z \lsim 2$ for multipoles $1000 \gsim l \gsim 100$: just the epoch when the dark energy starts to dominate the cosmological expansion rate. For scenarios having the same equation of state at the present, this turns out to be a new observable capable to discriminate between models of dark energy with different time evolution of equation of state. We assess the strength of this effetc within the framework of tracking Quintessence trajectories obeying SUGRA and Ratra-Peebles potentials.