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Angular Scales (angular + scale)
Selected AbstractsSunyaev,Zel'dovich effect from quasar-driven blast wavesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002P. Platania Abstract Quasar-driven winds are currently the best candidates for accounting for the pre-heating of the intergalactic medium in clusters. Such winds, occurring during early phases of the evolution of spheroidal galaxies, shock-heat the interstellar gas, thus inducing a detectable Sunyaev,Zel'dovich effect. We estimate the amplitude and the angular scale of such an effect as well as its counts as a function of the Comptonization parameter y. The contamination arising from radio emission by the quasar itself is also discussed. The corresponding mean Compton distortion of the cosmic microwave background spectrum is found to be well below the COBE/FIRAS upper limit. [source] Cosmic microwave background signal in Wilkinson Microwave Anisotropy Probe three-year data with fasticaMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007D. Maino ABSTRACT We present an application of the fast Independent Component Analysis (fastica) to the Wilkinson Microwave Anisotropy Probe (WMAP) three-year data with the goal of extracting the cosmic microwave background (CMB) signal. We evaluate the confidence of our results by means of Monte Carlo simulations including the CMB, foreground contaminations and instrumental noise specific to each WMAP frequency band. We perform a complete analysis involving all or a subset of the WMAP channels in order to select the optimal combination for CMB extraction, using the frequency scaling of the reconstructed component as a figure of merit. We find that the combination KQVW provides the best CMB frequency scaling, indicating that the low-frequency foreground contamination in Q, V and W bands is better traced by the emission in the K band. The CMB angular power spectrum is recovered up to the degree scale; it is consistent within errors for all WMAP channel combinations considered, and in close agreement with the WMAP three-year results. A power spectrum analysis is made of the sky map divided into two hemispheres that have been previously reported as showing evidence of an asymmetric ratio of power on large angular scales. We then confirm the findings of several previous works with independent techniques. [source] Reionization history from coupled cosmic microwave background/21-cm line dataMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2005R. Salvaterra ABSTRACT We study cosmic microwave background (CMB) secondary anisotropies produced by inhomogeneous reionization by means of cosmological simulations coupled with the radiative transfer code crash. The reionization history is consistent with the Wilkinson Microwave Anisotropy Probe Thomson optical depth determination. We find that the signal arising from this process dominates over the primary CMB component for l, 4000 and reaches a maximum amplitude of l(l+ 1)Cl/2,, 1.6 × 10,13 on arcmin scales (i.e. l as large as several thousands). We then cross-correlate secondary CMB anisotropy maps with neutral hydrogen 21-cm line emission fluctuations obtained from the same simulations. The two signals are highly anticorrelated on angular scales corresponding to the typical size of H ii regions (including overlapping) at the 21-cm map redshift. We show how the CMB/21-cm cross-correlation can be used: (i) to study the nature of the reionization sources; (ii) to reconstruct the cosmic reionization history; (iii) to infer the mean cosmic ionization level at any redshift. We discuss the feasibility of the proposed experiment with forthcoming facilities. [source] Analytical predictions for statistics of cosmic shear: tests against simulationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Patrick Valageas ABSTRACT Weak gravitational lensing surveys are rapidly becoming important tools to probe directly the mass density fluctuations in the Universe and its background dynamics. Earlier studies have shown that it is possible to model the statistics of the convergence field on small angular scales by suitably modelling the statistics of the underlying density field in the highly non-linear regime. We extend such methods to model the complete probability distribution function of the shear as a function of smoothing angle. Our model relies on a simple hierarchical Ansatz for the behaviour of the higher-order correlations in the density field. We compare our predictions with the results of numerical simulations and find excellent agreement for different cosmological scenarios. Our method provides a new way to study the evolution of non-Gaussianity in gravitational clustering and should help to break the degeneracies in parameter estimation based on analysis of the power spectrum alone. [source] From linear to non-linear scales: analytical and numerical predictions for weak-lensing convergenceMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2004Andrew J. Barber ABSTRACT Weak-lensing convergence can be used directly to map and probe the dark-mass distribution in the Universe. Building on earlier studies, we recall how the statistics of the convergence field are related to the statistics of the underlying mass distribution, in particular to the many-body density correlations. We describe two model-independent approximations which provide two simple methods to compute the probability distribution function (pdf) of the convergence. We apply one of these to the case where the density field can be described by a lognormal pdf. Next, we discuss two hierarchical models for the high-order correlations which allow us to perform exact calculations and evaluate the previous approximations in such specific cases. Finally, we apply these methods to a very simple model for the evolution of the density field from linear to highly non-linear scales. Comparisons with the results obtained from numerical simulations, obtained from a number of different realizations, show excellent agreement with our theoretical predictions. We have probed various angular scales in the numerical work and considered sources at 14 different redshifts in each of two different cosmological scenarios, an open cosmology and a flat cosmology with non-zero cosmological constant. Our simulation technique employs computations of the full three-dimensional shear matrices along the line of sight from the source redshift to the observer and is complementary to more popular ray-tracing algorithms. Our results therefore provide a valuable cross-check for such complementary simulation techniques, as well as for our simple analytical model, from the linear to the highly non-linear regime. [source] First stars contribution to the near-infrared background fluctuationsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003M. Magliocchetti ABSTRACT We show that the emission from the first, metal-free stars inside Population III objects (Pop IIIs) is needed to explain the level of fluctuations in the near-infrared background (NIRB) recently discovered by Kashlinsky et al., at least at the shortest wavelengths. Clustering of (unresolved) Pop IIIs can in fact account for the entire signal at almost all the ,1,30 arcsec scales probed by observations in the J band. Their contribution fades away at shorter frequencies and becomes negligible in the K band. ,Normal', highly clustered, ,z,, 3 galaxies undergoing intense star formation such as those found in the Hubble Deep Fields can ,fill in' this gap and provide for the missing signal. It is in fact found that their contribution to the intensity fluctuations is the dominant one at ,= 2.17 ,m, while it gradually loses importance in the H andJ bands. The joint contribution from these two populations of cosmic objects is able, within the errors, to reproduce the observed power spectrum in the whole near-infrared range on small angular scales (,, 200 arcsec for Pop III protogalaxies). Signals on larger scales detected by other experiments instead require the presence of more local sources. [source] Polarized diffuse emission at 2.3 GHz in a high Galactic latitude areaMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005E. Carretti ABSTRACT Polarized diffuse emission observations at 2.3 GHz in a high Galactic latitude area are presented. The 2°× 2° field, centred at (,= 5h, ,=,49°), is located in the region observed by the BOOMERanG experiment. Our observations were carried out with the Parkes radio telescope, and represent the highest frequency detection to date in a low-emission area. Because of the weaker Faraday rotation effect, the high frequency allows an estimate of the Galactic synchrotron contamination of the cosmic microwave background polarization (CMBP) which is more reliable than that achieved at 1.4 GHz. We find that the angular power spectra of the E - and B -modes have slopes of ,E=,1.46 ± 0.14 and ,B=,1.87 ± 0.22, indicating a flattening with respect to 1.4 GHz. Extrapolated up to 32 GHz, the E -mode spectrum is about three orders of magnitude lower than that of the CMBP, allowing a clean detection even at this frequency. The best improvement concerns the B -mode, for which our single-dish observations provide the first estimate of the contamination on angular scales close to the CMBP peak (about 2°). We find that the CMBP B -mode should be stronger than the synchrotron contamination at 90 GHz for models with tensor-to-scalar perturbation ratio T/S > 0.01. This low level could move down to 60,70 GHz the optimal window for CMBP measurements. [source] Primordial magnetic fields and CMB anisotropiesASTRONOMISCHE NACHRICHTEN, Issue 5-6 2006K. Subramanian Abstract Possible signatures of primordial magnetic fields on the Cosmic Microwave Background (CMB) temperature and polarization anisotropies are reviewed. The signals that could be searched for include excess temperature anisotropies particularly at small angular scales below the Silk damping scale, B-mode polarization, and non-Gaussian statistics. A field at a few nG level produces temperature anisotropies at the 5 µK level, and B-mode polarization anisotropies 10 times smaller, and is therefore potentially detectable via the CMB anisotropies. An even smaller field, with B0 < 0.1 nG, could lead to structure formation at high redshift z > 15, and hence naturally explain an early re-ionization of the Universe. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||