arXiv subjects

Tiziana Trombetti

Publications and source records attributed to Tiziana Trombetti.

27 records · Page 2Linked to original sources

arXiv2017

Characterization of polarimetric and total intensity behaviour of a complete sample of PACO radio sources in the radio bands

We present high sensitivity ($σ_P \simeq 0.6\,$mJy) polarimetric observations in seven bands, from $2.1$ to $38\,$GHz, of a complete sample of $104$ compact extragalactic radio sources brighter than $200\,$mJy at $20\,$GHz. Polarization measurements in six bands, in the range $5.5-38\,$GHz, for $53$ of these objects were reported by \citet{Galluzzi2017}. We have added new measurements in the same six bands for another 51 sources and measurements at $2.1\,$GHz for the full sample of $104$ sources. Also, the previous measurements at $18$, $24$, $33$ and $38\,$GHz were re-calibrated using the updated model for the flux density absolute calibrator, PKS1934-638, not available for the earlier analysis. The observations, carried out with the Australia Telescope Compact Array (ATCA), achieved a $90\%$ detection rate (at $5σ$) in polarization. $89$ of our sources have a counterpart in the $72$ to $231\,$MHz GLEAM survey \citep{HurleyWalker2017}, providing an unparalleled spectral coverage of $2.7$ decades of frequency for these sources. While the total intensity data from $5.5$ to $38\,$GHz could be interpreted in terms of single component emission, a joint analysis of more extended total intensity spectra presented here, and of the polarization spectra, reveals that over $90\%$ of our sources show clear indications of at least two emission components. We interpret this as an evidence of recurrent activity. Our high sensitivity polarimetry has allowed a $5\,σ$ detection of the weak circular polarization for $\sim 38\%$ of the dataset, and a deeper estimate of $20\,$GHz polarization source counts than has been possible so far.

astro-ph.GA↗

arXiv2016

On the impact of large angle CMB polarization data on cosmological parameters

(abridged) We study the impact of the large-angle CMB polarization datasets publicly released by the WMAP and Planck satellites on the estimation of cosmological parameters of the $Λ$CDM model. To complement large-angle polarization, we consider the high-resolution CMB datasets from either WMAP or Planck, as well as CMB lensing as traced by Planck. In the case of WMAP, we compute the large-angle polarization likelihood starting over from low-resolution frequency maps and their covariance matrices, and perform our own foreground mitigation technique, which includes as a possible alternative Planck 353 GHz data to trace polarized dust. We find that the latter choice induces a downward shift in the optical depth $τ$, of order ~$2σ$, robust to the choice of the complementary high-l dataset. When the Planck 353 GHz is consistently used to minimize polarized dust emission, WMAP and Planck 70 GHz large-angle polarization data are in remarkable agreement: by combining them we find $τ= 0.066 ^{+0.012}_{-0.013}$, again very stable against the particular choice for high-$\ell$ data. We find that the amplitude of primordial fluctuations $A_s$, notoriously degenerate with $τ$, is the parameter second most affected by the assumptions on polarized dust removal, but the other parameters are also affected, typically between $0.5$ and $1σ$. In particular, cleaning dust with \planck's 353 GHz data imposes a $1σ$ downward shift in the value of the Hubble constant $H_0$, significantly contributing to the tension reported between CMB based and direct measurements of $H_0$. On the other hand, we find that the appearance of the so-called low $\ell$ anomaly, a well-known tension between the high- and low-resolution CMB anisotropy amplitude, is not significantly affected by the details of large-angle polarization, or by the particular high-$\ell$ dataset employed.

astro-ph.CO↗

arXiv2016

Astrophysical components from Planck maps

The Planck Collaboration has recently released maps of the microwave sky in both temperature and polarization. Diffuse astrophysical components (including Galactic emissions, cosmic far infrared (IR) background, y-maps of the thermal Sunyaev-Zeldovich (SZ) effect) and catalogs of many thousands of Galactic and extragalactic radio and far-IR sources, and galaxy clusters detected through the SZ effect are the main astrophysical products of the mission. A concise overview of these results and of astrophysical studies based on Planck data is presented.

astro-ph.GA↗

arXiv2016

Recent results and perspectives on cosmology and fundamental physics from microwave surveys

Recent cosmic microwave background data in temperature and polarization have reached high precision in estimating all the parameters that describe the current so-called standard cosmological model. Recent results about the integrated Sachs-Wolfe effect from cosmic microwave background anisotropies, galaxy surveys, and their cross-correlations are presented. Looking at fine signatures in the cosmic microwave background, such as the lack of power at low multipoles, the primordial power spectrum and the bounds on non-Gaussianities, complemented by galaxy surveys, we discuss inflationary physics and the generation of primordial perturbations in the early Universe. Three important topics in particle physics, the bounds on neutrinos masses and parameters, on thermal axion mass and on the neutron lifetime derived from cosmological data are reviewed, with attention to the comparison with laboratory experiment results. Recent results from cosmic polarization rotation analyses aimed at testing the Einstein equivalence principle are presented. Finally, we discuss the perspectives of next radio facilities for the improvement of the analysis of future cosmic microwave background spectral distortion experiments.

astro-ph.CO↗

arXiv2015

SKA synergy with Microwave Background studies

The extremely high sensitivity and resolution of the Square Kilometre Array (SKA) will be useful for addressing a wide set of themes relevant for cosmology, in synergy with current and future cosmic microwave background (CMB) projects. Many of these themes also have a link with future optical-IR and X-ray observations. We discuss the scientific perspectives for these goals, the instrumental requirements and the observational and data analysis approaches, and identify several topics that are important for cosmology and astrophysics at different cosmic epochs.

astro-ph.CO↗

arXiv2013

Semi-analytical description of clumping factor and CMB free-free distortions from reionization

The density contrast of the Universe, parametrized in terms of the matter power spectrum and its variance, can amplify the signal of the free-free process in the plasma. The damping of fluctuations on scales smaller than the DM particle free streaming scale corresponds to a suppression of the total matter power spectrum on large wave numbers k. We derive the time evolution of the variance of the matter power spectrum for various cosmological models and parameters by numerically computing the power spectrum with a modified version of the Boltzmann code CAMB, for different values of the cut-off parameter kmax. Suitable analytical approximations of the numerical results are presented. We then characterize the CMB free-free spectral distortion accounting for the amplification effect coming from clumping factor. Indeed, the clumpiness, associated to the density contrast of the intergalactic medium, increases at decreasing redshift. The analysis is carried out for selected astrophysical and phenomenological cosmological reionization histories, for which we evaluate the impact of the clumping factor on the free-free distortion and discuss the wavelength dependence of the predicted signal. Finally, we address a comparison with other classes of unavoidable CMB spectral distortions and future observational perspectives. While Comptonization from reionization is dominant at high frequencies, the free-free signal predicted in the considered models contributes to the distortion at a level of few (few tens) per cent at frequencies below about 25 GHz (10 GHz) and represents the main signature below about 4 GHz. The cosmological signal from the HI 21-cm background is found to prevail over the free-free distortion in a restricted, model dependent frequency window between about 0.1 and 0.2 GHz.

astro-ph.CO↗

arXiv2013

PRISM (Polarized Radiation Imaging and Spectroscopy Mission): A White Paper on the Ultimate Polarimetric Spectro-Imaging of the Microwave and Far-Infrared Sky

PRISM (Polarized Radiation Imaging and Spectroscopy Mission) was proposed to ESA in response to the Call for White Papers for the definition of the L2 and L3 Missions in the ESA Science Programme. PRISM would have two instruments: (1) an imager with a 3.5m mirror (cooled to 4K for high performance in the far-infrared---that is, in the Wien part of the CMB blackbody spectrum), and (2) an Fourier Transform Spectrometer (FTS) somewhat like the COBE FIRAS instrument but over three orders of magnitude more sensitive. Highlights of the new science (beyond the obvious target of B-modes from gravity waves generated during inflation) made possible by these two instruments working in tandem include: (1) the ultimate galaxy cluster survey gathering 10e6 clusters extending to large redshift and measuring their peculiar velocities and temperatures (through the kSZ effect and relativistic corrections to the classic y-distortion spectrum, respectively) (2) a detailed investigation into the nature of the cosmic infrared background (CIB) consisting of at present unresolved dusty high-z galaxies, where most of the star formation in the universe took place, (3) searching for distortions from the perfect CMB blackbody spectrum, which will probe a large number of otherwise inaccessible effects (e.g., energy release through decaying dark matter, the primordial power spectrum on very small scales where measurements today are impossible due to erasure from Silk damping and contamination from non-linear cascading of power from larger length scales). These are but a few of the highlights of the new science that will be made possible with PRISM.

astro-ph.CO↗

arXiv2012

How accurately can we measure the hydrogen 2S->1S transition rate from the cosmological data?

Recent progress in observational cosmology, and especially the forthcoming PLANCK mission data, open new directions in so-called precision cosmology. In this paper we illustrate this statement considering the accuracy of cosmological determination of the two-quanta decay rate of 2s hydrogen atom state. We show that the PLANCK data will allow us to measure this decay rate significantly better than in the laboratory experiments.

astro-ph.CO↗

arXiv2012

CMB polarization anisotropies from cosmological reionization: extension to B-modes

The accurate understanding of the ionization history of the Universe plays a fundamental role in modern cosmology. It includes a phase of cosmological reionization after the standard recombination epoch, possibly associated to the early stages of structure and star formation. While the simple "τ-parametrization" of the reionization process and, in particular, of its imprints on the CMB anisotropy likely represents a sufficiently accurate modelling for the interpretation of current CMB data, a great attention has been recently posed on the accurate computation of the reionization signatures in the CMB for a large variety of astrophysical scenarios and physical processes. This work is aimed at a careful characterization of the imprints introduced in the polarization anisotropy, with particular attention to the B-modes. We have implemented a modified version of CAMB, the Cosmological Boltzmann code for computing the angular power spectrum (APS) of the anisotropies of the CMB, to introduce the hydrogen and helium ionization fractions predicted in astrophysical and phenomenological reionization histories, beyond the simple τ-parametrization. We compared the results obtained for these models for all the non-vanishing (in the assumed scenarios) modes of the CMB APS. The amplitude and shape of the B-mode APS depends, in particular, on the tensor-to-scalar ratio, r, and on the reionization history, thus an accurate modeling of the reionization process will have implications for the precise determination of r or to set more precise constraints on it through the joint analysis of E and B-mode polarization data available in the next future and from a mission of next generation. Considering also the limitation from potential residuals of astrophysical foregrounds, we discussed the capability of next data to disentangle between different reionization scenarios in a wide range of r.

astro-ph.CO↗