arXiv subjects

L. Toffolatti

Publications and source records attributed to L. Toffolatti.

44 records · Page 3Linked to original sources

arXiv1998

The effect of point sources on satellite observations of the cosmic microwave background

We study the effect of extragalactic point sources on satellite observations of the cosmic microwave background (CMB). In order to separate the contributions due to different foreground components, a maximum-entropy method is applied to simulated observations by the Planck Surveyor satellite. In addition to point sources, the simulations include emission from the CMB and the kinetic and thermal Sunyaev-Zel'dovich (SZ) effects from galaxy clusters, as well as Galactic dust, free-free and synchrotron emission. We find that the main input components are faithfully recovered and, in particular, that the quality of the CMB reconstruction is only slightly reduced by the presence of point sources. In addition, we find that it is possible to recover accurate point source catalogues at each of the Planck Surveyor observing frequencies.

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arXiv1998

Extragalactic Point Sources and the Planck Surveyor Mission

We review estimates of small scale fluctuations due to extragalactic point sources in the Planck Surveyor frequency bands. While our undestanding of the spectral and evolutionary properties of these sources is far from complete, conservative estimates allow us to confidently conclude that, in the frequency range 100--200 GHz, their contaminating effect is well below the expected anisotropy level of the cosmic microwave background (CMB), down to angular scales of at least $\simeq 10'$. Hence, an accurate subtraction of foreground fluctuations is not critical for the determination of the CMB power spectrum up to multipoles $\ell \simeq 1000$. In any case, Planck's wide frequency coverage will allow to carefully control foreground contributions.On the other hand, the all sky surveys at 9 frequencies, spanning the range 30--900 GHz, will be unique in providing complete samples comprising from several hundreds to many thousands of extragalactic sources, selected in an essentially unexplored frequency region. New classes of sources may be revealed in these data. The familiar ``flat''-spectrum radio sources should show spectral features carrying essential information on their physical properties. Crucial information will be provided to understand the nature of radio sources with strongly inverted spectra. Scenarios for the cosmological evolution of galaxies will be extensively tested.

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arXiv1998

Extragalactic Source Counts and Contributions to the Anisotropies of the Cosmic Microwave Background. Predictions for the Planck Surveyor mission

We present predictions for the counts of extragalactic sources, the contributions to fluctuations and their spatial power spectrum in each channel foreseen for the Planck Surveyor (formerly COBRAS/SAMBA) mission. The contribution to fluctuations due to clustering of both radio and far--IR sources is found to be generally small in comparison with the Poisson term; however the relative importance of the clustering contribution increases and may eventually become dominant if sources are identified and subtracted down to faint flux limits. The central Planck frequency bands are expected to be ``clean'': at high galactic latitude (|b|>20), where the reduced galactic noise does not prevent the detection of the extragalactic signal, only a tiny fraction of pixels is found to be contaminated by discrete extragalactic sources. Moreover, removal of contaminating signals is eased by the substantial difference between their power spectrum and that of primordial fluctuations.

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arXiv1995

SUB--DEGREE ANISOTROPY OBSERVATIONS: GROUND--BASED, BALLOON--BORNE AND SPACE EXPERIMENTS

Extensive, accurate imaging of the Cosmic Background Radiation temperature anisotropy at sub--degree angular resolution is widely recognized as one of the most crucial goals for cosmology and astroparticle physics in the next decade. We review the scientific case for such measurements in relation with sky coverage, attainable sensitivity, confusing foreground radiation components, and experimental strategies. Although ground--based and balloon--borne experiments will provide valuable results, only a well--designed, far--Earth orbit space mission covering a wide spectral range and a significant part of all the sky will provide decisive answers on the mechanism of structure formation.

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arXiv1994

Foreground Contributions to 0.2-2 Degree CMB Anisotropies

We examine the extent to which galactic and extragalactic foregrounds can hamper the detection of primordial Cosmic Microwave Background (CMB) anisotropies. We limit our discussion to intermediate angular scales, $10^{\prime}\lsim θ\lsim 2^{\circ}$, since many current as well as future experiments have been designed to map CMB anisotropies at these angular scales. In fact, scales of $\gsim 10^{\prime}$ are of crucial importance to test both the conditions in the early Universe and current theories of the gravitational collapse.

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arXiv1994

The Extragalactic IR Background

Current limits on the intensity of the extragalactic infrared background are consistent with the expected contribution from evolving galaxies. Depending on the behaviour of the star formation rate and of the initial mass function, we can expect that dust extinction during early evolutionary phases ranges from moderate to strong. An example of the latter case may be the ultraluminous galaxy IRAS F$10214 + 4724$. The remarkable lack of high redshift galaxies in faint optically selected samples may be indirect evidence that strong extinction is common during early phases. Testable implications of different scenarios are discussed; ISO can play a key role in this context. Estimates of possible contributions of galaxies to the background under different assumptions are presented. The COBE/FIRAS limits on deviations from a blackbody spectrum at sub-mm wavelengths already set important constraints on the evolution of the far-IR emission of galaxies and on the density of obscured (``Type 2'') AGNs. A major progress in the field is expected at the completion of the analysis of COBE/DIRBE data.

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arXiv1993

Angular Correlations of the X-Ray Background and Clustering of Extragalactic X-Ray Sources

The information content of the autocorrelation function (ACF) of intensity fluctuations of the X-ray background (XRB) is analyzed. The tight upper limits set by ROSAT deep survey data on the ACF at arcmin scales imply strong constraints on clustering properties of X-ray sources at cosmological distances and on their contribution to the soft XRB. If quasars have a clustering radius r_0=12-20 Mpc (H_0=50), and their two point correlation function, is constant in comoving coordinates as indicated by optical data, they cannot make up more 40-50% of the soft XRB (the maximum contribution may reach 80% in the case of stable clustering, epsilon=0). Active Star-forming (ASF) galaxies clustered like normal galaxies, with r_0=10-12 Mpc can yield up to 20% or up to 40% of the soft XRB for epsilon=-1.2 or epsilon=0, respectively. The ACF on degree scales essentially reflects the clustering properties of local sources and is proportional to their volume emissivity. The upper limits on scales of a few degrees imply that hard X-ray selected AGNs have r_0<25 Mpc if epsilon=0 or r_0<20 Mpc if epsilon=-1.2. No significant constraints are set on clustering of ASF galaxies, due to their low local volume emissivity. The possible signal on scales >6 deg, if real, may be due to AGNs with r_0=20 Mpc; the contribution from clusters of galaxies with r_0~50 Mpc is a factor 2 lower.

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arXiv1993

Background Radiation

We present a short overview on the extragalactic background radiation from radio to X-rays, with an eye to the relation to galaxy formation and emphasizing on astrophysical backgrounds (as opposed to cosmological). As the radio background, the wealth of data on source counts make possible reliable estimations of the contribution from extragalactic sources. At 178 MHz we obtain an antenna temperature of about 22 K, with the 60% of the flux contributed by radiogalaxies and quasars and the remaining part from sub-mJy radio sources. At high frequencies the compact sources, generally QSOs, dominate. An intense far-IR/sub-mm background is predicted if a large fraction of the hard X-ray Background (XRB) comes from starburst galaxies but this might face problems with the upper limits on the far-IR isotropic flux. To clarify the problem spectral measurements should be complemented with the analysis of small scale anisotropies. The flattening of the QSO counts at B=19.5 suggests that their contribution to the optical/near-IR background is small in comparison to that of galaxies. As for the XRB, a consisting picture obtains considering two AGN populations: a "soft X-ray spectrum" population and a "hard X-ray spectrum" one, mainly contributing to the soft and to the hard XRB respectively. A third population of extremely absorbed or of reflection dominated AGN could either be the dominant contributor of the XRB above 3 keV.

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