Foreground removal for Square Kilometre Array observations of the Epoch of Reionization with the Correlated Component Analysis

We apply the Correlated Component Analysis (CCA) method on simulated data of the Square Kilometre Array, with the aim of accurately cleaning the 21 cm reionization signal from diffuse foreground contamination. The CCA has been developed for the Cosmic Microwave Background, but the application of the Fourier-domain implementation of this method to the reionization signal is straightforward. The CCA is a parametric method to estimate the frequency behaviour of the foregrounds from the data by using second-order statistics. We test its performance on foreground simulations of increasing complexity, designed to challenge the parametric models adopted. We also drop the assumption of spectral smoothness that most of the methods rely upon. We are able to clean effectively the simulated data across the explored frequency range (100-200 MHz) for all the foreground simulations. This shows that the CCA method is very promising for EoR component separation.Comment: 12 pages, 15 figures, accepted by MNRA

Foreground removal requirements for measuring large-scale CMB B-modes in light of BICEP2

The most convincing confirmation that the B-mode polarization signal detected at degree scales by BICEP2 is due to the Cosmic Microwave Background (CMB) would be the measurement of its large-scale counterpart. We assess the requirements for diffuse component separation accuracy over large portions of the sky in order to measure the large-scale B-mode signal corresponding to a tensor to scalar ratio of r=0.1-0.2. We use the method proposed by Bonaldi & Ricciardi (2011) to forecast the performances of different simulated experiments taking into account noise and foreground removal issues. We do not consider instrumental systematics, and we implicitly assume that they are not the dominant source of error. If this is the case, the confirmation of an r=0.1-0.2 signal is achievable by Planck even for conservative assumptions regarding the accuracy of foreground cleaning. Our forecasts suggest that the combination of this experiment with BICEP2 will lead to an improvement of 25-45% in the constraint on r. A next-generation CMB polarization satellite, represented in this work by the COrE experiment, can reduce dramatically (by almost another order of magnitude) the uncertainty on r. In this case, however, the accuracy of foreground removal becomes critical to fully benefit from the increase in sensitivity.Comment: 8 pages, 3 figures, 1 table. Accepted by MNRA

Sunyaev-Zel'dovich profiles and scaling relations: modelling effects and observational biases

We use high-resolution hydrodynamic re-simulations to investigate the properties of the thermal Sunyaev-Zel'dovich (SZ) effect from galaxy clusters. We compare results obtained using different physical models for the intracluster medium (ICM), and show how they modify the SZ emission in terms of cluster profiles and scaling relations. We also produce realistic mock observations to verify whether the results from hydrodynamic simulations can be confirmed. We find that SZ profiles depend marginally on the modelled physical processes, while they exhibit a strong dependence on cluster mass. The central and total SZ emission strongly correlate with the cluster X-ray luminosity and temperature. The logarithmic slopes of these scaling relations differ from the self-similar predictions by less than 0.2; the normalization of the relations is lower for simulations including radiative cooling. The observational test suggests that SZ cluster profiles are unlikely to be able to probe the ICM physics. The total SZ decrement appears to be an observable much more robust than the central intensity, and we suggest using the former to investigate scaling relations.Comment: 13 pages, 12 figures, accepted by MNRA

Cosmological constraints from Sunyaev-Zeldovich cluster counts: an approach to account for missing redshifts

The accumulation of redshifts provides a significant observational bottleneck when using galaxy cluster surveys to constrain cosmological parameters. We propose a simple method to allow the use of samples where there is a fraction of the redshifts that are not known. The simplest assumption is that the missing redshifts are randomly extracted from the catalogue, but the method also allows one to take into account known selection effects in the accumulation of redshifts. We quantify the reduction in statistical precision of cosmological parameter constraints as a function of the fraction of missing redshifts for simulated surveys, and also investigate the impact of making an incorrect assumption for the distribution of missing redshifts.Comment: 6 pages, 5 figures, accepted by Ap

A new model of the microwave polarized sky for CMB experiments

We present a new model of the microwave sky in polarization that can be used to simulate data from CMB polarization experiments. We exploit the most recent results from the Planck satellite to provide an accurate description of the diffuse polarized foreground synchrotron and thermal dust emission. Our model can include the two mentioned foregrounds, and also a constructed template of Anomalous Microwave Emission (AME). Several options for the frequency dependence of the foregrounds can be easily selected, to reflect our uncertainties and to test the impact of different assumptions. Small angular scale features can be added to the foreground templates to simulate high-resolution observations. We present tests of the model outputs to show the excellent agreement with Planck and WMAP data. We determine the range within which the foreground spectral indices can be varied to be consistent with the current data. We also show forecasts for a high-sensitivity, high-resolution full-sky experiment such as the Cosmic ORigin Explorer (COrE). Our model is released as a python script that is quick and easy to use, available at \url{http://www.jb.man.ac.uk/~chervias}.Comment: 12 pages, 14 Figures, 1 Table, Accepted by MNRA

SKA Weak Lensing III: Added Value of Multi-Wavelength Synergies for the Mitigation of Systematics

In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinise synergies between cosmic shear measurements in the radio and optical/near-IR bands for mitigating systematic effects. We focus on three main classes of systematics: (i) experimental systematic errors in the observed shear; (ii) signal contamination by intrinsic alignments; and (iii) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multi-wavelength analysis provides a self-calibration method for experimental systematic effects, only implying <50% increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 0.00001, i.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarisation information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher-redshift bins of radio catalogues peak at z~0.8-1, whereas their optical/near-IR counterparts are limited to z<0.5-0.7. This translates into having a cosmological signal 2 to 5 times less contaminated by non-linear perturbations.Comment: 16 pages, 10 figures, 2 tables; improved discussion of experimental systematics in Sec. 2; updated to match published versio

SKA Weak Lensing II: Simulated Performance and Survey Design Considerations

We construct a pipeline for simulating weak lensing cosmology surveys with the Square Kilometre Array (SKA), taking as inputs telescope sensitivity curves; correlated source flux, size and redshift distributions; a simple ionospheric model; source redshift and ellipticity measurement errors. We then use this simulation pipeline to optimise a 2-year weak lensing survey performed with the first deployment of the SKA (SKA1). Our assessments are based on the total signal-to-noise of the recovered shear power spectra, a metric that we find to correlate very well with a standard dark energy figure of merit. We first consider the choice of frequency band, trading off increases in number counts at lower frequencies against poorer resolution; our analysis strongly prefers the higher frequency Band 2 (950-1760 MHz) channel of the SKA-MID telescope to the lower frequency Band 1 (350-1050 MHz). Best results would be obtained by allowing the centre of Band 2 to shift towards lower frequency, around 1.1 GHz. We then move on to consider survey size, finding that an area of 5,000 square degrees is optimal for most SKA1 instrumental configurations. Finally, we forecast the performance of a weak lensing survey with the second deployment of the SKA. The increased survey size (3$\pi$\,steradian) and sensitivity improves both the signal-to-noise and the dark energy metrics by two orders of magnitude.Comment: 15 pages, 11 figures, 1 table. Comments welcome. Updated to match published versio

A new map-making algorithm for CMB polarisation experiments

With the temperature power spectrum of the cosmic microwave background (CMB) at least four orders of magnitude larger than the B-mode polarisation power spectrum, any instrumental imperfections that couple temperature to polarisation must be carefully controlled and/or removed. Here we present two new map-making algorithms that can create polarisation maps that are clean of temperature-to-polarisation leakage systematics due to differential gain and pointing between a detector pair. Where a half wave plate is used, we show that the spin-2 systematic due to differential ellipticity can also by removed using our algorithms. The algorithms require no prior knowledge of the imperfections or temperature sky to remove the temperature leakage. Instead, they calculate the systematic and polarisation maps in one step directly from the time ordered data (TOD). The first algorithm is designed to work with scan strategies that have a good range of crossing angles for each map pixel and the second for scan strategies that have a limited range of crossing angles. The first algorithm can also be used to identify if systematic errors that have a particular spin are present in a TOD. We demonstrate the use of both algorithms and the ability to identify systematics with simulations of TOD with realistic scan strategies and instrumental noise.Comment: 11 pages, 6 figure

Selective readout and back-action reduction for wideband acoustic gravitational wave detectors

We present the concept of selective readout for broadband resonant mass gravitational wave detectors. This detection scheme is capable of specifically selecting the signal from the contributions of the vibrational modes sensitive to the gravitational waves, and efficiently rejecting the contribution from non gravitationally sensitive modes. Moreover this readout, applied to a dual detector, is capable to give an effective reduction of the back-action noise within the frequency band of interest. The overall effect is a significant enhancement in the predicted sensitivity, evaluated at the standard quantum limit for a dual torus detector. A molybdenum detector, 1 m in diameter and equipped with a wide area selective readout, would reach spectral strain sensitivities 2x10^{-23}/sqrt{Hz} between 2-6 kHz.Comment: 9 pages, 4 figure

Harmonic damped oscillators with feedback. A Langevin study

We consider a system in direct contact with a thermal reservoir and which, if left unperturbed, is well described by a memory-less equilibrium Langevin equation of the second order in the time coordinate. In such conditions, the strength of the noise fluctuations is set by the damping factor, in accordance with the Fluctuation and Dissipation theorem. We study the system when it is subject to a feedback mechanism, by modifying the Langevin equation accordingly. Memory terms now arise in the time evolution, which we study in a non-equilibrium steady state. Two types of feedback schemes are considered, one focusing on time shifts and one on phase shifts, and for both cases we evaluate the power spectrum of the system's fluctuations. Our analysis finds application in feedback cooled oscillators, such as the Gravitational Wave detector AURIGA.Comment: 17 page