We summarize the results of the Cosmic Microwave Background (CMB) working group of the ARENA project. The focus has been on precision measurements of CMB polarization (looking for the echoes of cosmological inflation) and high angular resolution CMB measurements (looking for Sunyaev Zeldovich effect in distant clusters of Galaxies, to probe the evolution of the Universe, Dark Matter and Dark Energy). For both projects the Dome C site represents the best choice worldwide.

Cosmic Microwave Background observations became the tool to probe the the first events of cosmic history. After WMAP data releases, galactic and extragalactic foregrounds are perceived as the main limiting uncertainity for the near-future search for the B-mode polarization inprints from the inflationary era, either through satellites or ground-based experiments like Brain at Dome-C. A combination of technology, scanning strategy and above all, accurate knowledge of polarized foregrounds will be necessary for an optimal mapping of B-mode CMB Polarization. In addition, the search for a better understanding of the galactic foregrounds will provide unprecedented knowledge on the Milky Way structure and star formation.

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) has recently conducted an extragalactic submillimetric survey of the Chandra Deep Field South region of unprecedented size, depth, and angular resolution in three wavebands centered at 250, 350, and 500 µm. BLAST wavelengths are chosen to study the Cosmic Infrared Background near its peak at 200 µm. We find that most of the CIB at these wavelengths is contributed by galaxies detected at 24 µm by the MIPS instrument on Spitzer, and that the source counts distribution shows a population with strongly evolving density and luminosity. These results anticipate what can be expected from the surveys that will be conducted with the SPIRE instrument on the Herschel space observatory.

BOOMERanG has recently resolved structures on the last scattering surface at redshift ˜ 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.

The ClOVER instrument (described elsewhere in this volume) is being built to measure the B-mode polarisation of the Cosmic Microwave Background. Each of the 256 pixels is made up a pseudo-correlation receiver that can be realised using either waveguide or microstrip technology. In this work we present a design study for a possible waveguide-based solution. Each of the individual components has been optimised using electromagnetic finite-element modelling software (HFSS).

In the 1998-99 flight, BOOMERanG has produced maps of ∼4% of the sky at high Galactic latitudes, at frequencies of 90, 150, 240 and 410 GHz, with resolution ≳ 10'. The faint structure of the Cosmic Microwave Background at horizon and sub-horizon scales is evident in these maps. These maps compare well to the maps recently obtained at lower frequencies by the WMAP experiment. Here we compare the amplitude and morphology of the structures observed in the two sets of maps. We also outline the polarization sensitive version of BOOMERanG, which was flown early this year to measure the linear polarization of the microwave sky at 150, 240 and 350 GHz.

In the current cosmological scenario, part of the linearly polarized emission of the CMB is expected to be rotational (B-modes). This component is due to tensor perturbations of the metric produced by primordial gravitational waves, which are generated a split-second after the Big Bang. The signal expected is of the order of ≲ 0.1 μK, well below the non-rotational component of the polarization signal (E-modes), and beyond the sensitivity of present generation instruments. New, more sensitive instruments are developed in several labs, with the goal to measure the B-modes. Control of systematics and foregrounds will be the key to make the results of these experiments believable. In this paper we shortly outline BRAIN, a bolometric interferometer devoted to B-modes research, and its pathfinder experiment, devoted to test the Dome-C site.


We present a new, fully-funded ground-based instrument designed to measure the B-mode polarization of the Cosmic Microwave Background (CMB). The concept is based on three independent sub-systems operating at 90, 150 and 220 GHz, each comprising a telescope and a focal plane of horn-coupled background-limited bolometers. This highly-sensitive experiment, planned to be based at Dome C station in Antarctica, is optimised to produce very low systematic effects. It will allow the detection of the CMB polarization over angular multipoles 20<l<1000 accurately enough to measure the B-mode signature from gravitational waves to a lensing-confusion-limited tensor-to-scalar ratio r ~ 0.005.

CASPER (Concordia Atmospheric SPectroscopy of Emitted Radiation) is a spectrometer proposed for installation at Dome C, devoted to measurements of atmospheric emission in the spectral region between 180 μm and 3 mm (3–55 cm-1). This instrument will be able to perform continuous spectral sampling at different altitudes at angular scales of ~1°. From the recorded data it is possible to extract atmospheric transmittance within 1% in the whole wide operating band, together with water vapour content and O2 and O3 concentrations. CASPER will allow us to characterize the site for future FIR/mm telescopes. Atmospheric data recorded by CASPER will allow for correction of astrophysical and cosmological observations without the need for telescope-specific procedures and further loss of observation time with more precision in the observations themselves. Calibration of ground-based telescopes on known sky sources is strongly affected by atmospheric absorption. CASPER has this as its primary goal. The spectrometer is based on a Martin-Puplett interferometer. Two data sampling solutions will be performed: phase modulation & fast scan strategy. Sky radiation is collected towards the interferometer by an optical setup that allows the field of view, to explore the full 0° ÷ 90° range of elevation angles. With a low spurious polarization instrument, monitoring of polarized atmospheric contribution will be possible.

We show how estimates of parameters characterizing inflation-based theories of structure formation localized over the past year when large scale structure (LSS) information from galaxy and cluster surveys was combined with the rapidly developing cosmic microwave background (CMB) data, especially from the recent Boomerang and Maxima balloon experiments. All current CMB data plus a relatively weak prior probability on the Hubble constant, age and LSS points to little mean curvature (Ωtot = 1.08±0.06) and nearly scale invariant initial fluctuations (ns = 1.03±0.08), both predictions of (non-baroque) inflation theory. We emphasize the role that degeneracy among parameters in the Lpk = 212 ± 7 position of the (first acoustic) peak plays in defining the Ωtot range upon marginalization over other variables. Though the CDM density is in the expected range (Ωcdmh2 = 0.17 ± 0.02), the baryon density Ωbh2 = 0.030 ± 0.005 is somewhat above the independent 0.019 ± 0.002 nucleosynthesis estimates. CMB+LSS gives independent evidence for dark energy (ΩΛ = 0.66 ± 0.06) at the same level as from supernova (SN1) observations, with a phenomenological quintessence equation of state limited by SN1+CMB+LSS to wQ < −0.7 cf. the wQ=−1 cosmological constant case.