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