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Scientific Report 2007-2009<br />
Astronomy & Astrophysics<br />
to different parameters of the cosmological model, and have produced compelling evidence for a<br />
homogeneous and isotropic background universe, where adiabatic inflationary perturbations have<br />
produced the large-scale structure we see today via gravitational instability.<br />
Today, the activities of the group focus on the<br />
finest details of the Cosmic Microwave Background.<br />
We observe the interaction of CMB<br />
photons with the hot plasma in clusters of galaxies<br />
(the Sunyaev-Zeldovich effect) both from the<br />
MITO telescope (covering efficiently the frequencies<br />
in the atmospheric windows up to 240 GHz,<br />
and complemented by a performing atmospheric<br />
monitor, CASPER) (A12) and from the balloonborne<br />
telescope OLIMPO (covering frequencies up<br />
to 480 GHz) (A13). There is a net energy transfer<br />
from hot electrons to CMB photons, so that the<br />
CMB spectrum shifts towards high frequencies in<br />
the direction of a cluster, with a very characteristic<br />
spectral signature. This effect allows to detect<br />
very distant clusters, using them as cosmological<br />
probes, and to study the peripheral regions of the<br />
intergalactic plasma, where the density is too low<br />
to produce significant X-ray emission. With the<br />
High Frequency Instrument on the Planck satellite,<br />
to which we contributed with the development<br />
of flight hardware ( including all the cryogenic<br />
preamplifiers) of the calibrations and of data analysis,<br />
we study the primary anisotropy of the CMB<br />
with an unprecedented combination of angular<br />
resolution, sensitivity, and frequency coverage.<br />
The measurements of Planck will settle all the<br />
issues on CMB anisotropy, producing definitive<br />
Figure 4: Map of the cosmic microwave background<br />
obtained at 145 GHz by the BOOMERanG experiment,<br />
built in our department, during its second<br />
fight devoted to the measurement of the polarization<br />
in the CMB (from Masi et al., 2006). The structures<br />
visible in the map are produced by density and velocity<br />
fluctuations in the primeval plasma, at redshift z<br />
≃ 1100. The angular power spectrum of this image<br />
constrains efficiently the cosmological parameters.<br />
maps of the microwave sky in a very wide frequency range, thus allowing reliable subtraction of<br />
foregrounds. Moreover, they will improve our knowledge of CMB polarization, and put significant<br />
constraints on the B-modes produced by inflation. We investigate CMB polarization with the<br />
BRAIN polarimeter, installed at the Concordia base on the high Antarctic plateau. This is a<br />
pathfinder for a large bolometric interferometer, the QUBIC experiment, in the framework of<br />
a large international collaboration. For the near future, we are developing new ultra-sensitive<br />
measurements of CMB polarization, to be carried out from a balloon platform, in preparation of<br />
a large post-Planck satellite mission (A14). In preparation of this, we are developing our own<br />
large format arrays of millimeter detectors, based on kinetic inductance resonators, and we are<br />
carrying out intensive technological research with the development of large cryostats for liquid<br />
helium in space (we have recently qualified porous plugs) and cryogenic polarization modulators<br />
with negligible heat load (A15). A new horizon opened recently with our proposal to study the<br />
wavelength spectrum of CMB anisotropy, by means of space-borne Differential Fourier Transform<br />
Spectrometers (DFTS). With the phase-A study of the SAGACE mission we have demonstrated<br />
the impact of this methodology in the study of the SZ effect, of the cooling lines in primeval<br />
galaxies (expecially [CII], of microwave emission from AGNs. All these experimental activities<br />
are complemented by a vigorous interpretation activity, based on the simultaneous analysis of<br />
different cosmological observables in the framework of the adiabatic inflationary model. This<br />
approach has been very successful in estimating and constraining several parameters of the<br />
cosmological model (like the average mass-energy density in the Universe Ω o , the average density<br />
<strong>Sapienza</strong> Università di Roma 146 Dipartimento di Fisica