arXiv subjects

G. de Gasperis

Publications and source records attributed to G. de Gasperis.

At least 55 records · Page 3Linked to original sources

arXiv2011

Planck Early Results: Statistical properties of extragalactic radio sources in the Planck Early Release Compact Source Catalogue

The data reported in Planck's Early Release Compact Source Catalogue (ERCSC) are exploited to measure the number counts (dN/dS) of extragalactic radio sources at 30, 44, 70, 100, 143 and 217 GHz. Due to the full-sky nature of the catalogue, this measurement extends to the rarest and brightest sources in the sky. At lower frequencies (30, 44, and 70 GHz) our counts are in very good agreement with estimates based on WMAP data, being somewhat deeper at 30 and 70 GHz, and somewhat shallower at 44 GHz. Planck's source counts at 143 and 217 GHz join smoothly with the fainter ones provided by the SPT and ACT surveys over small fractions of the sky. An analysis of source spectra, exploiting Planck's uniquely broad spectral coverage, finds clear evidence of a steepening of the mean spectral index above about 70 GHz. This implies that, at these frequencies, the contamination of the CMB power spectrum by radio sources below the detection limit is significantly lower than previously estimated.

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arXiv2011

Planck Early Results: The Planck View of Nearby Galaxies

The all-sky coverage of the Planck Early Release Compact Source Catalogue (ERCSC) provides an unsurpassed survey of galaxies at submillimetre (submm) wavelengths, representing a major improvement in the numbers of galaxies detected, as well as the range of far-IR/submm wavelengths over which they have been observed. We here present the first results on the properties of nearby galaxies using these data. We match the ERCSC catalogue to IRAS-detected galaxies in the Imperial IRAS Faint Source Redshift Catalogue (IIFSCz), so that we can measure the spectral energy distributions (SEDs) of these objects from 60 to 850 microns. This produces a list of 1717 galaxies with reliable associations between Planck and IRAS, from which we select a subset of 468 for SED studies, namely those with strong detections in the three highest frequency Planck bands and no evidence of cirrus contamination. The SEDs are fitted using parametric dust models to determine the range of dust temperatures and emissivities. We find evidence for colder dust than has previously been found in external galaxies, with T<20K. Such cold temperatures are found using both the standard single temperature dust model with variable emissivity beta, or a two dust temperature model with beta fixed at 2. We also compare our results to studies of distant submm galaxies (SMGs) which have been claimed to contain cooler dust than their local counterparts. We find that including our sample of 468 galaxies significantly reduces the distinction between the two populations. Fits to SEDs of selected objects using more sophisticated templates derived from radiative transfer models confirm the presence of the colder dust found through parameteric fitting. We thus conclude that cold (T<20K) dust is a significant and largely unexplored component of many nearby galaxies.

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arXiv2011

Planck Early Results: The Galactic Cold Core Population revealed by the first all-sky survey

We present the statistical properties of the first version of the Cold Core Catalogue of Planck Objects (C3PO), in terms of their spatial distribution, temperature, distance, mass, and morphology. We also describe the statistics of the Early Cold Core Catalogue (ECC, delivered with the Early Release Compact Source Catalogue, ERCSC) that is the subset of the 915 most reliable detections of the complete catalogue. We have used the CoCoCoDeT algorithm to extract 10783 cold sources. Temperature and dust emission spectral index β values are derived using the fluxes in the IRAS 100 \mum band and the three highest frequency Planck bands. Temperature spans from 7K to 17K, and peaks around 13K. Data are not consistent with a constant value of β over the all temperature range. β ranges from 1.4 to 2.8 with a mean value around 2.1, and several possible scenarios are possible, including β(T) and the effect of multiple T components folded into the measurements. For one third of the objects the distances are obtained. Most of the detections are within 2 kpc in the Solar neighbourhood, but a few are at distances greater than 4 kpc. The cores are distributed from the deep Galactic plane, despite the confusion, to high latitudes (>30$^{\circle}$). The associated mass estimates range from 1 to $10^5$ solar masses. Using their physical properties these cold sources are shown to be cold clumps, defined as the intermediate cold sub-structures between clouds and cores. These cold clumps are not isolated but mostly organized in filaments associated with molecular clouds. The Cold Core Catalogue of Planck Objects (C3PO) is the first unbiased all-sky catalogue of cold objects. It gives an unprecedented statistical view to the properties of these potential pre-stellar clumps and offers a unique possibility for their classification in terms of their intrinsic properties and environment.

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arXiv2011

Planck Early Results: Origin of the submm excess dust emission in the Magellanic Clouds

The integrated Spectral Energy Distributions of the Large and Small Magellanic Cloud appear significantly flatter than expected from dust models based on their FIR and radio emission. The origin of this millimetre excess is still unexplained, and is here investigated using the Planck data. The background CMB contribution is subtracted using an ILC method performed locally around the galaxies. The foreground emission from the Milky Way is subtracted. After subtraction, the emission of both galaxies correlates closely with the gas emission of the LMC and SMC. The millimetre excess in the LMC can be explained by CMB fluctuations, but a significant excess is still present in the SMC SED. The Planck and IRIS data at 100 micron are combined to produce thermal dust temperature and optical depth maps of the two galaxies. The LMC temperature map shows the presence of a warm inner arm already found with the Spitzer data, but also shows the existence of a previously unidentified cold outer arm. Several cold regions are found along this arm, some of which are associated with known molecular clouds. The average emissivity spectral index is found to be consistent with beta=1.5 and beta=1.2 below 500 microns for the LMC and SMC respectively, significantly flatter than the values observed in the Milky Way. Furthermore, there is evidence in the SMC for a further flattening of the SED in the sub-mm. The spatial distribution of the millimetre dust excess in the SMC follows the gas and thermal dust distribution. Different models are explored in order to fit the dust emission in the SMC. It is concluded that the millimetre excess is unlikely to be caused by very cold dust emission and that it could be due to a combination of spinning dust. emission and thermal dust emission by more amorphous dust grains than those present in our Galaxy.

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arXiv2011

Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy

We construct an all-sky map of the apparent temperature and optical depth of thermal dust emission using the Planck-HFI and IRAS data. The optical depth maps are correlated to tracers of the atomic and molecular gas. The correlation is linear in the lowest column density regions at high galactic latitudes. At high NH, the correlation is consistent with that of the lowest NH. In the intermediate NH range, we observe departure from linearity, with the dust optical depth in excess to the correlation. We attribute this excess emission to thermal emission by dust associated with a Dark-Gas phase, undetected in the available HI and CO measurements. We show the 2D spatial distribution of the Dark-Gas in the solar neighborhood and show that it extends around known molecular regions traced by CO. The average dust emissivity in the HI phase in the solar neighborhood follows roughly a power law distribution with beta = 1.8 all the way down to 3 mm, although the SED flattens slightly in the millimetre. The threshold for the existence of the Dark-Gas is found at NH = (8.0\pm 0.58) 10^{20} Hcm-2. Assuming the same dust emissivity at high frequencies for the dust in the atomic and molecular phases leads to an average XCO = (2.54\pm0.13) 10^{20} H2cm-2/(K km s-1). The mass of Dark-Gas is found to be 28% of the atomic gas and 118% of the CO emitting gas in the solar neighborhood. A possible origin for the Dark-Gas is the existence of a dark molecular phase, where H2 survives photodissociation but CO does not. The observed transition for the onset of this phase in the solar neighborhood (AV = 0.4 mag) appears consistent with recent theoretical predictions. We also discuss the possibility that up to half of the Dark-Gas could be in atomic form, due to optical depth effects in the HI measurements.

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arXiv2011

Planck Early Results: The submillimetre properties of a sample of Galactic cold clumps

(abridged) We perform a detailed investigation of sources from the Cold Cores Catalogue of Planck Objects (C3PO). Our goal is to probe the reliability of the detections, validate the separation between warm and cold dust emission components, provide the first glimpse at the nature, internal morphology and physical characterictics of the Planck-detected sources. We focus on a sub-sample of ten sources from the C3PO list, selected to sample different environments, from high latitude cirrus to nearby (150pc) and remote (2kpc) molecular complexes. We present Planck surface brightness maps and derive the dust temperature, emissivity spectral index, and column densities of the fields. With the help of higher resolution Herschel and AKARI continuum observations and molecular line data, we investigate the morphology of the sources and the properties of the substructures at scales below the Planck beam size.

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arXiv2011

Planck early results: Cluster Sunyaev-Zeldovich optical scaling relations

We present the Sunyaev-Zeldovich (SZ) signal-to-richness scaling relation (Y500-N200) for the MaxBCG cluster catalogue. Employing a multi-frequency matched filter on the Planck sky maps, we measure the SZ signal for each cluster by adapting the filter according to weak-lensing calibrated mass-richness relations (N200-M500). We bin our individual measurements and detect the SZ signal down to the lowest richness systems (N200=10) with high significance, achieving a detection of the SZ signal in systems with mass as low as M500~5e13 Msolar. The observed Y500-N200 relation is well modeled by a power law over the full richness range. It has a lower normalisation at given N200 than predicted based on X-ray models and published mass-richness relations. An X-ray subsample, however, does conform to the predicted scaling, and model predictions do reproduce the relation between our measured bin-average SZ signal and measured bin-average X-ray luminosities. At fixed richness, we find an intrinsic dispersion in the Y500-N200 relation of 60% rising to of order 100% at low richness. Thanks to its all-sky coverage, Planck provides observations for more than 13,000 MaxBCG clusters and an unprecedented SZ/optical data set, extending the list of known cluster scaling laws to include SZ-optical properties. The data set offers essential clues for models of galaxy formation. Moreover, the lower normalisation of the SZ-mass relation implied by the observed SZ-richness scaling has important consequences for cluster physics and cosmological studies with SZ clusters.

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arXiv2010

Clouds, filaments and protostars: the Herschel Hi-GAL Milky Way

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key-project that will map the inner Galactic Plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2° x 2° tiles approximately centered at l=30° and l=59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call 'cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around A_V of about 1 is exceeded for the regions in the l=59° field; a A_V value between 5 and 10 is found for the l=30° field, likely due to the relatively larger distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm-2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.

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arXiv2010

Planck pre-launch status: the Planck-LFI programme

This paper provides an overview of the Low Frequency Instrument (LFI) programme within the ESA Planck mission. The LFI instrument has been developed to produce high precision maps of the microwave sky at frequencies in the range 27-77 GHz, below the peak of the cosmic microwave background (CMB) radiation spectrum. The scientific goals are described, ranging from fundamental cosmology to Galactic and extragalactic astrophysics. The instrument design and development are outlined, together with the model philosophy and testing strategy. The instrument is presented in the context of the Planck mission. The LFI approach to ground and inflight calibration is described. We also describe the LFI ground segment. We present the results of a number of tests demonstrating the capability of the LFI data processing centre (DPC) to properly reduce and analyse LFI flight data, from telemetry information to calibrated and cleaned time ordered data, sky maps at each frequency (in temperature and polarization), component emission maps (CMB and diffuse foregrounds), catalogs for various classes of sources (the Early Release Compact Source Catalogue and the Final Compact Source Catalogue). The organization of the LFI consortium is briefly presented as well as the role of the core team in data analysis and scientific exploitation. All tests carried out on the LFI flight model demonstrate the excellent performance of the instrument and its various subunits. The data analysis pipeline has been tested and its main steps verified. In the first three months after launch, the commissioning, calibration, performance, and verification phases will be completed, after which Planck will begin its operational life, in which LFI will have an integral part.

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arXiv2009

Foreground influence on primordial non-Gaussianity estimates: needlet analysis of WMAP 5-year data

We constrain the amplitude of primordial non-Gaussianity in the CMB data taking into account the presence of foreground residuals in the maps. We generalise the needlet bispectrum estimator marginalizing over the amplitudes of thermal dust, free-free and synchrotron templates. We apply our procedure to WMAP 5 year data, finding fNL= 38\pm 47 (1 σ), while the analysis without marginalization provides fNL= 35\pm 42. Splitting the marginalization over each foreground separately, we found that the estimates of fNL are positively cross correlated of 17%, 12% with the dust and synchrotron respectively, while a negative cross correlation of about -10% is found for the free-free component.

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arXiv2009

New estimates of the CMB angular power spectra from the WMAP 5 yrs low resolution data

A Quadratic Maximum Likelihood (QML) estimator is applied to the WMAP 5 year low resolution maps to compute the CMB angular power spectra at large scales for both temperature and polarization. Estimates and error bars for the six angular power spectra are provided and compared, when possible, to those obtained by the WMAP team, without finding any inconsistency. The conditional likelihood slices are also computed for the $C_{\ell}$ of all the six power spectra from $\ell =2$ to 10 through a pixel based likelihood code. Both the codes treat the covariance for $(T,Q,U)$ in a single matrix without employing any approximation. The inputs of both the codes (foreground reduced maps and related covariances) are provided by the WMAP team. The peaks of the likelihood slices are always consistent with the QML estimates within the error bars, however an excellent agreement occurs when the QML estimates are used as fiducial power spectrum instead of the best-fit theoretical power spectrum. By the full computation of the conditional likelihood on the estimated spectra, the value of the temperature quadrupole $C_{\ell=2}^{TT}$ is found to be less than $2 σ$ away from the WMAP 5 yrs $Λ$CDM best-fit value. The $BB$ spectrum is found well consistent with zero and upper limits on the B-modes are provided. The parity odd signals $TB$ and $EB$ are found consistent with zero.

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arXiv2009

Residual noise covariance for Planck low-resolution data analysis

Aims: Develop and validate tools to estimate residual noise covariance in Planck frequency maps. Quantify signal error effects and compare different techniques to produce low-resolution maps. Methods: We derive analytical estimates of covariance of the residual noise contained in low-resolution maps produced using a number of map-making approaches. We test these analytical predictions using Monte Carlo simulations and their impact on angular power spectrum estimation. We use simulations to quantify the level of signal errors incurred in different resolution downgrading schemes considered in this work. Results: We find an excellent agreement between the optimal residual noise covariance matrices and Monte Carlo noise maps. For destriping map-makers, the extent of agreement is dictated by the knee frequency of the correlated noise component and the chosen baseline offset length. The significance of signal striping is shown to be insignificant when properly dealt with. In map resolution downgrading, we find that a carefully selected window function is required to reduce aliasing to the sub-percent level at multipoles, ell > 2Nside, where Nside is the HEALPix resolution parameter. We show that sufficient characterization of the residual noise is unavoidable if one is to draw reliable contraints on large scale anisotropy. Conclusions: We have described how to compute the low-resolution maps, with a controlled sky signal level, and a reliable estimate of covariance of the residual noise. We have also presented a method to smooth the residual noise covariance matrices to describe the noise correlations in smoothed, bandwidth limited maps.

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arXiv2009

BOOMERanG Constraints on Primordial Non-Gaussianity from Analytical Minkowski Functionals

We use Minkowski Functionals (MF) to constrain a primordial non-Gaussian contribution to the CMB intensity field as observed in the 150 GHz and 145 GHz BOOMERanG maps from the 1998 and 2003 flights, respectively, performing for the first time a joint analysis of the two datasets. A perturbative expansion of the MF formulae in the limit of a weakly non-Gaussian field yields analytical formulae, derived by Hikage et al. (2006), which can be used to constrain the coupling parameter f_NL without the need for non-Gaussian simulations. We find -1020<f_NL<390 at 95% CL, significantly improving the previous constraints by De Troia et al. (2007) on the BOOMERanG 2003 dataset. These are the best f_NL limits to date for suborbital probes.

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arXiv2009

Making Maps from Planck LFI 30GHz Data with Asymmetric Beams and Cooler Noise

The Planck satellite will observe the full sky at nine frequencies from 30 to 857 GHz. The goal of this paper is to examine the effects of four realistic instrument systematics in the 30 GHz frequency maps: non-axially-symmetric beams, sample integration, sorption cooler noise, and pointing errors. We simulated one year long observations of four 30 GHz detectors. The simulated timestreams contained CMB, foreground components (both galactic and extra-galactic), instrument noise (correlated and white), and the four instrument systematic effects. We made maps from the timelines and examined the magnitudes of the systematics effects in the maps and their angular power spectra. We also compared the maps of different mapmaking codes to see how they performed. We used five mapmaking codes (two destripers and three optimal codes). None of our mapmaking codes makes an attempt to deconvolve the beam from its output map. Therefore all our maps had similar smoothing due to beams and sample integration. Temperature to polarization cross-coupling due to beam mismatch causes a detectable bias in the TE spectrum of the CMB map. The effects of cooler noise and pointing errors did not appear to be major concerns for the 30 GHz channel. The only essential difference found so far between mapmaking codes that affects accuracy (in terms of residual RMS) is baseline length. All optimal codes give essentially indistinguishable results. A destriper gives the same result as the optimal codes when the baseline is set short enough. For longer baselines destripers require less computing resources but deliver a noisier map.

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arXiv2007

Making Maps from Planck LFI 30GHz Data

This paper is one of a series describing the performance and accuracy of map-making codes as assessed by the Planck CTP working group. We compare the performance of multiple codes written by different groups for making polarized maps from Planck-sized, all-sky cosmic microwave background (CMB) data. Three of the codes are based on destriping algorithm, whereas the other three are implementations of a maximum-likelihood algorithm. Previous papers in the series described simulations at 100 GHz (Poutanen et al. 2006) and 217 GHz (Ashdown et al. 2006). In this paper we make maps (temperature and polarisation) from the simulated one-year observations of four 30 GHz detectors of Planck Low Frequency Instrument (LFI). We used Planck Level S simulation pipeline to produce the observed time-ordered-data streams (TOD). Our previous studies considered polarisation observations for the CMB only. For this paper we increased the realism of the simulations and included polarized galactic foregrounds to our sky model. Our simulated TODs comprised of dipole, CMB, diffuse galactic emissions, extragalactic radio sources, and detector noise. The strong subpixel signal gradients arising from the foreground signals couple to the output map through the map-making and cause an error (signal error) in the maps. Destriping codes have smaller signal error than the maximum-likelihood codes. We examined a number of schemes to reduce this error. On the other hand, the maximum-likelihood map-making codes can produce maps with lower residual noise than destriping codes.

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arXiv2006

Making sky maps from Planck data

We compare the performance of multiple codes written by different groups for making polarized maps from Planck-sized, all-sky cosmic microwave background (CMB) data. Three of the codes are based on a destriping algorithm; the other three are implementations of an optimal maximum-likelihood algorithm. Time-ordered data (TOD) were simulated using the Planck Level-S simulation pipeline. Several cases of temperature-only data were run to test that the codes could handle large datasets, and to explore effects such as the precision of the pointing data. Based on these preliminary results, TOD were generated for a set of four 217 GHz detectors (the minimum number required to produce I, Q, and U maps) under two different scanning strategies, with and without noise. Following correction of various problems revealed by the early simulation, all codes were able to handle the large data volume that Planck will produce. Differences in maps produced are small but noticeable; differences in computing resources are large.

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arXiv2005

Comparison of map-making algorithms for CMB experiments

We have compared the cosmic microwave background (CMB) temperature anisotropy maps made from one-year time ordered data (TOD) streams that simulated observations of the originally planned 100 GHz Planck Low Frequency Instrument (LFI). The maps were made with three different codes. Two of these, ROMA and MapCUMBA, were implementations of maximum-likelihood (ML) map-making, whereas the third was an implementation of the destriping algorithm. The purpose of this paper is to compare these two methods, ML and destriping, in terms of the maps they produce and the angular power spectrum estimates derived from these maps. The difference in the maps produced by the two ML codes was found to be negligible. As expected, ML was found to produce maps with lower residual noise than destriping. In addition to residual noise, the maps also contain an error which is due to the effect of subpixel structure in the signal on the map-making method. This error is larger for ML than for destriping. If this error is not corrected a bias will be introduced in the power spectrum estimates. This study is related to Planck activities.

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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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