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N. Vittorio

Publications and source records attributed to N. Vittorio.

At least 37 records · Page 2Linked to original sources
arXiv2002

CMB Power Spectrum Estimation for the Planck Surveyor

We use an iterative generalized least squares map-making algorithm, in conjunction with Monte Carlo techniques, to obtain estimates of the angular power spectrum from cosmic microwave background (CMB) maps. This is achieved by characterizing and removing the instrumental noise contribution in multipole space. This technique produces unbiased estimates and can be applied to an arbitrary experiment. In this paper, we use it on realistic simulations of Planck Low Frequency Instrument (LFI) observations, showing that it can lead to fast and reliable estimation of the CMB angular power spectrum from megapixel maps.

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arXiv2002

Scalar field dark energy and Cosmic Microwave Background

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, {\sc Planck} and {\sc 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 $2σ$.

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arXiv2002

Search for non-gaussian signals in the BOOMERanG maps: pixel-space analysis

We search the BOOMERanG maps of the anisotropy of the Cosmic Microwave Background (CMB) for deviations from gaussianity. In this paper we focus on analysis techniques in pixel-space, and compute skewness, kurtosis and Minkowski functionals for the BOOMERanG maps and for gaussian simulations of the CMB sky. We do not find any significant deviation from gaussianity in the high galactic latitude section of the 150 GHz map. We do find deviations from gaussianity at lower latitudes and at 410 GHz, and we ascribe them to Galactic dust contamination. Using non-gaussian simulations of instrumental systematic effects, of foregrounds, and of sample non-gaussian cosmological models, we set upper limits to the non-gaussian component of the temperature field in the BOOMERanG maps. For fluctuations distributed as a 1 DOF $χ^2$ mixed to the main gaussian component our upper limits are in the few % range.

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arXiv2002

The BOOMERanG experiment and the curvature of the Universe

We describe the BOOMERanG experiment and its main result, i.e. the measurement of the large scale curvature of the Universe. BOOMERanG is a balloon-borne microwave telescope with sensitive cryogenic detectors. BOOMERanG has measured the angular distribution of the Cosmic Microwave Background on $\sim 3%$ of the sky, with a resolution of $\sim 10$ arcmin and a sensitivity of $\sim 20 μK$ per pixel. The resulting image is dominated by hot and cold spots with rms fluctuations $\sim 80 μK$ and typical size of $\sim 1^o$. The detailed angular power spectrum of the image features three peaks and two dips at $\ell = (213^{+10}_{-13}), (541^{+20}_{-32}), (845^{+12}_{-25})$ and $\ell = (416^{+22}_{-12}), (750^{+20}_{-750})$, respectively. Such very characteristic spectrum can be explained assuming that the detected structures are the result of acoustic oscillations in the primeval plasma. In this framework, the measured pattern constrains the density parameter $Ω$ to be $0.85 < Ω< 1.1$ (95% confidence interval). Other cosmological parameters, like the spectral index of initial density fluctuations, the density parameter for baryons, dark matter and dark energy, are detected or constrained by the BOOMERanG measurements and by other recent CMB anisotropy experiments. When combined with other cosmological observations, these results depict a new, consistent, cosmological scenario.

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arXiv2001

Non-iterative methods to estimate the in-flight noise properties of CMB detectors

We present a new approach for statistical inference on noise properties of CMB anisotropy data. We consider a Maximum Likelihood parametric estimator to recover the full dependence structure of the noise process. We also consider a semiparametric procedure which is only sensitive to the low frequency behavior of the noise spectral density. Both approaches are statistically robust and computationally convenient in the case of long memory noise, even under nonstationary circumstances. We show that noise properties can be consistently derived by such procedures without resorting to currently used iterative noise-signal methods. More importantly, we show that optimal (GLS) CMB maps can be obtained from the observed timestream with the only knowledge of the noise memory parameter, the outcome of our estimators.

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arXiv2001

CMB Polarization: Scientific Case and Data Analysis Issues

We review the science case for studying CMB polarization. We then discuss the main issues related to the analysis of forth-coming polarized CMB data, such as those expected from balloon-borne (e.g. BOOMERanG) and satellite (e.g. Planck) experiments.

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arXiv2001

What's Behind Acoustic Peaks in the Cosmic Microwave Background Anisotropies

We give a brief review of the physics of acoustic oscillations in Cosmic Microwave Background (CMB) anisotropies. As an example of the impact of their detection in cosmology, we show how the present data on CMB angular power spectrum on sub-degree scales can be used to constrain dark energy cosmological models.

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arXiv2001

On the primordial helium content: CMB and stellar constraints

We present the results of a joint investigation aimed at constraining the primordial He content ($Y_P$) on the basis of both the Cosmic Microwave Background (CMB) anisotropy and two stellar observables, namely the tip of the Red Giant Branch (TRGB) and the luminosity of the Zero Age Horizontal Branch (ZAHB). Current baryon density estimates based on CMB measurements cover a wide range values $0.009\la Ω_bh^2 \la 0.045$, that according to Big Bang Nucleosynthesis (BBN) models would imply $0.24\la Y_P \la 0.26$. We constructed several sets of evolutionary tracks and HB models by adopting $Y_P=0.26$ and several metal contents. The comparison between theory and observations suggests that ZAHB magnitudes based on He-enhanced models are 1.5$σ$ brighter than the empirical ones. The same outcome applies for the TRGB bolometric magnitudes. This finding somewhat supports a $Y_P$ abundance close to the canonical 0.23-0.24 value. More quantitative constraints on this parameter are hampered by the fact that the CMB pattern shows a sizable dependence on both $Y_P$ and the baryon density only at small angular scales, i.e. at high l in the power spectrum ($l\ga 100$). However, this region of the power spectrum could be still affected by deceptive systematic uncertainties. Finally, we suggest to use the {\em UV-upturn} to estimate the He content on Gpc scales. In fact, we find that a strong increase in $Y_P$ causes in metal-poor, hot HB structures a decrease in the UV emission.

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arXiv2001

A Map-Making Algorithm for the Planck Surveyor

We present a parallel implementation of a map-making algorithm for CMB anisotropy experiments which is both fast and efficient. We show for the first time a Maximum Likelihood, minimum variance map obtained by processing the entire data stream expected from the Planck Surveyor, under the assumption of a symmetric beam profile. Here we restrict ourselves to the case of the 30 GHz channel of the Planck Low Frequency Instrument. The extension to Planck higher frequency channels is straightforward. If the satellite pointing periodicity is good enough to average data that belong to the same sky circle, then the code runs very efficiently on workstations. The serial version of our code also runs on very competitive time-scales the map-making pipeline for current and forthcoming balloon borne experiments.

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arXiv2000

In-flight main beam reconstruction for Planck-LFI

In-flight measurement of the antenna main beams of the Planck instruments is a crucial input to the data analysis pipeline. We study the main beam reconstruction achievable through external planets using a flight simulator to model their observation. We restrict our analysis to the 30 GHz LFI channel but the method can be easily extended to higher frequency channels. We show that it is possible to fit the antenna response from Jupiter and Saturn to obtain an accurate, robust, simple and fast reconstruction of the main beam properties under very general conditions, independently of the calibration accuracy. In addition, we find that a bivariate Gaussian approximation of the main beam shapes represents a significant improvement with respect to a symmetric representation. We also show that it is possible to combine the detection of the planet's transit and Planck's very accurate in-flight calibration to measure the planet's temperature at millimetric wavelengths with an accuracy at the % level. This work is based on Planck-LFI activities.

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arXiv2000

Detection of anisotropy in the Cosmic Microwave Background at horizon and sub-horizon scales with the BOOMERanG experiment

BOOMERanG has recently resolved structures on the last scattering surface at redshift $\sim$ 1100 with high signal to noise ratio. We review the technical advances which made this possible, and we focus on the current results for maps and power spectra, with special attention to the determination of the total mass-energy density in the Universe and of other cosmological parameters.

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arXiv2000

First results from the BOOMERanG experiment

We report the first results from the BOOMERanG experiment, which mapped at 90, 150, 240 and 410 GHz a wide (3%) region of the microwave sky with minimal local contamination. From the data of the best 150 GHz detector we find evidence for a well defined peak in the power spectrum of temperature fluctuations of the Cosmic Microwave Background, localized at $\ell = 197 \pm 6$, with an amplitude of $(68 \pm 8) μK_{CMB}$. The location, width and amplitude of the peak is suggestive of acoustic oscillations in the primeval plasma. In the framework of inflationary adiabatic cosmological models the measured spectrum allows a Bayesian estimate of the curvature of the Universe and of other cosmological parameters. With reasonable priors we find $Ω= (1.07 \pm 0.06)$ and $n_s = (1.00 \pm 0.08)$ (68%C.L.) in excellent agreement with the expectations from the simplest inflationary theories. We also discuss the limits on the density of baryons, of cold dark matter and on the cosmological constant.

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arXiv2000

Implications for quintessence models from MAXIMA-1 and BOOMERANG-98

Prompted by the recent MAXIMA-1 and BOOMERANG-98 measurements of the cosmic microwave background (CMB) anisotropy power spectrum, and motivated by the results from the observation of high-redshift Type Ia supernovae, we investigate CMB anisotropies in quintessence models in order to characterize the nature of the dark energy today. We perform a Bayesian likelihood analysis, using the MAXIMA-1 and BOOMERANG-98 published bandpowers, in combination with COBE/DMR, to explore the space of quintessence parameters: the quintessence energy density Ω_ϕand equation of state w_ϕ. We restrict our analysis to flat, scale-invariant, inflationary adiabatic models. We find that this simple class of inflationary models, with a quintessence component Ω_ϕ< ~0.7, -1 < = w_ϕ< ~-0.5, is in good agreement with the data. Within the assumptions of our analysis, pure quintessence models seem to be slightly favored, although the simple cosmological constant scenario is consistent with the data.

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arXiv2000

A Flat Universe from High-Resolution Maps of the Cosmic Microwave Background Radiation

The blackbody radiation left over from the Big Bang has been transformed by the expansion of the Universe into the nearly isotropic 2.73K Cosmic Microwave Background. Tiny inhomogeneities in the early Universe left their imprint on the microwave background in the form of small anisotropies in its temperature. These anisotropies contain information about basic cosmological parameters, particularly the total energy density and curvature of the universe. Here we report the first images of resolved structure in the microwave background anisotropies over a significant part of the sky. Maps at four frequencies clearly distinguish the microwave background from foreground emission. We compute the angular power spectrum of the microwave background, and find a peak at Legendre multipole $\ell_{peak}=(197 \pm 6)$, with an amplitude $DT_{200}=(69 \pm 8)μK$. This is consistent with that expected for cold dark matter models in a flat (euclidean) Universe, as favoured by standard inflationary scenarios.

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arXiv1999

A measurement of Omega from the North American test flight of BOOMERANG

We use the angular power spectrum of the Cosmic Microwave Background, measured during the North American test flight of the BOOMERANG experiment, to constrain the geometry of the universe. Within the class of Cold Dark Matter models, we find that the overall fractional energy density of the universe, Omega, is constrained to be 0.85 < Omega < 1.25 at the 68% confidence level. Combined with the COBE measurement and the high redshift supernovae data we obtain new constraints on the fractional matter density and the cosmological constant.

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arXiv1999

Measurement of a Peak in the Cosmic Microwave Background Power Spectrum from the North American test flight of BOOMERANG

We describe a measurement of the angular power spectrum of anisotropies in the Cosmic Microwave Background (CMB) from 0.3 degrees to ~10 degrees from the North American test flight of the BOOMERANG experiment. BOOMERANG is a balloon-borne telescope with a bolometric receiver designed to map CMB anisotropies on a Long Duration Balloon flight. During a 6-hour test flight of a prototype system in 1997, we mapped > 200 square degrees at high galactic latitudes in two bands centered at 90 and 150 GHz with a resolution of 26 and 16.6 arcmin FWHM respectively. Analysis of the maps gives a power spectrum with a peak at angular scales of ~1 degree with an amplitude ~70 uK.

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arXiv1999

The Planck Surveyor mission: astrophysical prospects

Although the Planck Surveyor mission is optimized to map the cosmic microwave background anisotropies, it will also provide extremely valuable information on astrophysical phenomena. We review our present understanding of Galactic and extragalactic foregrounds relevant to the mission and discuss on one side, Planck's impact on the study of their properties and, on the other side, to what extent foreground contamination may affect Planck's ability to accurately determine cosmological parameters. Planck's multifrequency surveys will be unique in their coverage of large areas of the sky (actually, of the full sky); this will extend by two or more orders of magnitude the flux density interval over which mm/sub-mm counts of extragalactic sources can be determined by instruments already available (like SCUBA) or planned for the next decade (like the LSA-MMA or the space mission FIRST), which go much deeper but over very limited areas. Planck will thus provide essential complementary information on the epoch-dependent luminosity functions. Bright radio sources will be studied over a poorly explored frequency range where spectral signatures, essential to understand the physical processes that are going on, show up. The Sunyaev-Zeldovich effect, with its extremely rich information content, will be observed in the direction of a large number of rich clusters of Galaxies. Thanks again to its all sky coverage, Planck will provide unique information on the structure and on the emission properties of the interstellar medium in the Galaxy. At the same time, the foregrounds are unlikely to substantially limit Planck's ability to measure the cosmological signals. Even measurements of polarization of the primordial Cosmic Microwave background fluctuations appear to be feasible.

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