February 13, 2012

Planck: new results on the foregrounds

ESA's Planck mission news release: our galaxy contains unknown cold gas clouds as well as a mysterious microwave sail. These new results were announced this week during an international symposium in Bologna.

The first carbon monoxide map was presented

The first carbon monoxide complete sky map was released during the Bologna symposium on February 13th-17th 2012. The carbon monoxide is one of the components of cold clouds which are present in the galaxies and especially in the Milky Way Galaxy. Mainly composed of hydrogen molecules, these clouds are like reservoirs from which the stars form. However, the hydrogen molecules are difficult to detect.

Even if carbon monoxide is less abundant, it forms in similar conditions and emits specific radiations. For this reason, the astronomers use it like a marker in order to map the hydrogen clouds. “It turns out that Planck is an excellent carbon monoxide detector over the entire sky”, Jonathan Aumont, from the Institute of Astrophysics of Paris, said.

The carbon monoxide observation campaigns carried out from radio telescopes required a lot of time and were thus limited to sky portions where molecular clouds are supposed to exist. “The great benefit of Planck is that it systematically scan the entire sky and this specification allowed molecular gas concentrations to be detected where they are not expected to exist”, Jonathan Aumont added.

Sky charts which show the carbon monoxide distribution, a marker of molecular clouds, detected by the Planck satellite's HFI (High Frequency Instrument). The large structures on the background result from data processing artefacts and do not have anything real.
At the bottom, superimposed in red, the previous 2001 map (the outlines indicate the observed area). Many molecular clouds are located in remote locations on the galactic plan and were still unknown.
Credit: ESA/consortia HFI/LFI+ T. dame and al., 2001 (image below)

Unexplained microwave emission at the very heart of our galaxy

Planck also showed a mysterious microwave sail which remains unexplained.

This sail comes from the region surrounding the galactic centre and appears in a similar form to what the scientists call the  "synchrotron emission". The latter is produced by electron passages - previously accelerated by supernova explosions - in magnetic fields. This radiation discloses what the investigators call a "harder" spectrum (its emission does not decrease so quickly when the energy increases) than observed elsewhere in the Milky Way Galaxy for this type of emission.

In order to explain this curious behaviour, many hypothesis were told such as a higher supernova rate, galactic winds or even the dark matter particle annihilation. Until now, none of these hypothesis could be confirmed.

The Planck's multiple sciences

The first Planck mission's objective was to observe the cosmic microwave background (CMB), a remainder of the Big-Bang and the most remote light we receive, and decode the information this light contains on the universe, its elemental components, origin and structure.

For this purpose, all the other foreground emissions have to be identified and separated. In fact, the Planck's large spectral range (from 300 microns to approximately 11 mm) covers emissions coming from different sources such as interstellar dust clouds, myriads of galaxies in the sky or even clusters of galaxies: monsters which alter the spectrum and so the CMB's apparent temperature. In addition, since the Planck's detectors are very sensitive to highly energetic particles of the cosmic radiation, the data have to be cleaned to remove the bombardment's effects.

A consortium of specialists is responsible for carrying out this hard task, which requires a very accurate understanding of the instrument operations and astrophysics in general. France is especially responsible for analysing the HFI's measurements which supply 6 of the 8 Planck's measurement channels. Supported by CNES, a large number of laboratories of the CNRS (INSU and IN2P3) and CEA, under the coordination of the Institute of Astrophysics of Paris which hosts the supercomputer performing the calculations, are at work since well before the launch of Planck.

This effort, which already brought results on the foregrounds (symposium in La Villette in 2011 and now in Bologna), will result in the CMB emission map release in 2013, with an unprecedented accuracy.

Articles references

The announcement of these discoveries precedes the publishing of the articles. The references will be completed at a later stage.

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