At the beginning there was light (photons!). The primordial Universe was hot, matter was completely ionized and its dynamics was governed by a huge radiation bath. As the Universe expanded and cooled, the atoms formed (380 000 years after the Big-Bang) and this radiation bath could finally escape carrying the imprints of the forming Large Scale Structure (the small temperature fluctuations are like a xerox copy of the matter fluctuations at the time). Nowadays, with almost 14 thousand million years of Cosmic History, this radiation bath forms the Cosmic Microwave Background Radiation (CMBR), detected for the first time in 1965 and mapped for the first time with the DMR instrument aboard COBE satellite in 1992. George Smoot, PI of COBE/DMR, the GEM mentor, was awarded the Physics Nobel Prize in 2006 for this discovery.
The study of the CMBR, of its temperature small fluctuations (about ~50~80 μK) and its polarization small variations (1-10 μK) are in the vanguard of cosmologic probes. It allow us to reconstitute, with great precision the cosmic history and to determinate the geometry, age and contents of the Universe.
But the signal is partially obscured by radiation emitted by the Milky Way. To help quantifying this galactic contamination, the GEM project will map the sky with high sensitivity and absolute calibration, literally lifting the veil to the CMBR.
figure 1 - Galactic
For a better understanding of the phenomenology of polarization foregrounds (galactic dust emission, galactic synchrotron and free-free emission, figure 1), that contaminate the Cosmic Microwave Background signal to detect, namely with the Planck Surveyor satellite - ESA, launch by 2007. We plan to survey the North Hemisphere polarized galactic emission at 5 and 10 GHz with a 9-meter dish antenna installed in Central Portugal (see simulations). This will complement the South Hemisphere survey carried by the Brasil team. Together, both surveys will produce an almost complete sky template (~85% sky coverage) of the polarization states of the synchrotron emission. At these observing frequencies, Faraday rotation depolarization is negligible thus permitting a better extrapolation for the Component Separation Techniques in the CMBR data processing.
These polarization templates are also relevant for galactic dynamics providing the means to map the global galactic magnetic field.
The galaxy (synchrotron emission) as seen by the WMAP satellite
The antenna with its receiver will be installed in Fajão - Pampilhosa da Serra (Long. 7º 52' W, Lat. 40º 11' N ; Alt: 839 meters. ).
The sky coverage we should expect :
Portugal Survey (2007)
Common region The 5 GHz Mosaic (2007-)
This project has the support from Fundação para Ciência e Tecnologia (Portugal) through grants POCI/CTE-AST/57209/2004 and POCTI/FNU/42263/2001 and Câmara Municipal de Pampilhosa da Serrra
We acknowledge Portugal Telecom, TEGAEL, SOMAGUE Engenharia for their support.
We also acknowledgeEng. Luis Vale and family, owners of the land where the antenna will be installed.
Related GEM pages: