QUIXOTE maps the polarization of the microwave emission of the Milky Way

After almost a decade since it began its observations of the northern hemisphere sky, the QUIJOTE collaboration has presented, in an initial series of 6 studies, the most precise description to date of the polarization of the microwave emission of the Milky Way. This is an observation window never before explored and that provides complementary information to that obtained by some space missions (Planck and WMAP) dedicated to the study of the cosmic microwave background, the fossil radiation from the Big Bang. The new results allow us to obtain information on the structure of the magnetic field of our galaxy and will help to understand the energetic processes that took place at the birth of the universe.

The QUIJOTE experiment is located at the Teide Observatory (Izaña, Tenerife, Spain) and is made up of two 2.25 m diameter telescopes that observe the sky in the microwave domain (10-40 GHz). Led by the Instituto de Astrofísica de Canarias (IAC) in Spain, this experiment began its observations in 2012. Now, thanks to the data obtained with its MFI multifrequency instrument, which was in operation until 2018, a scientific team has presented a series of six studies in the academic journal Monthly Notices of the Royal Astronomical Society (MNRAS) in which the most accurate description to date of the polarization of microwave emission processes in our galaxy is made.

“These maps provide a detailed description of the sky in a new frequency range, from 10 to 20 GHz, complementary to space missions that have previously observed the sky in microwaves, such as Planck (ESA) and WMAP (NASA)”, comments José Alberto Rubiño, scientific manager of QUIJOTE and principal investigator of the European RADIOFOREGROUNDS project. “We have characterized with unprecedented precision the polarization of the synchrotron emission from our galaxy, which is the result of the emission of charged particles moving at speeds close to the speed of light within the galactic magnetic field. These maps, the result of almost 9,000 hours of observation, are a unique tool for studying magnetism in the universe”, he adds.

Map of polarized microwave emissions in the sky of the Earth’s northern hemisphere. The color scale represents the intensity of the emission. (Image: QUIXOTE Collaboration. CC BY)

Polarized Synchrotron and the Cosmic Microwave Background

The cosmic microwave background is a fossil radiation that comes from the first moments of the universe and that we observe today in the domain of radio waves. This kind of radiation is studied by scientists because, “by investigating its polarization properties, we intend to find the indirect trace of the existence of gravitational waves generated after the Big Bang”, comments Ricardo Génova-Santos (IAC).

To access that signal from the early universe, scientists must remove the emission veil associated with our galaxy. The new QUIXOTE maps provide a tool to carry out this task. “One of the most interesting results we have found is that the polarized synchrotron emission from our galaxy is much more spatially variable than previously thought,” says Elena de la Hoz, a researcher at the Cantabria Institute of Physics (IFCA) in Spain. “The results obtained constitute a reference to help future experiments to detect the cosmological signal,” she adds.

“The detection of said cosmological signal, a very specific pattern in the polarization of the microwave background associated with the presence of gravitational waves generated during the so-called inflationary era, would open a new window to fundamental Physics,” Rubiño underlines, “allowing us to explore scales of energy trillions of times higher than those that can currently be explored from Earth with particle accelerators. And he adds: “Your study of it would allow us to understand the energetic processes that took place at the birth of the universe.”

abnormal microwave emission

The new QUIJOTE data are also a unique tool for studying anomalous microwave emission (EAM), a type of emission first detected some 25 years ago, thought to be produced by rotating dust particles. very small cells in the interstellar medium that tend to orient themselves due to the presence of the galactic magnetic field.

“The polarization properties of these emissions have to be characterized and understood in detail in order to decontaminate the polarization maps of the cosmic microwave background for cosmology”, comments Frederick Poidevin, a researcher at the IAC. “With the new data from QUIXOTE we have improved our understanding of EAM in multiple regions of our galaxy,” says Denis Tramonte, a researcher at the Purple Mountain Observatory, under the Chinese Academy of Sciences.

Other results

The QUIXOTE maps have also made it possible to study the microwave emission coming from the galactic center. An excess of microwave emission of still unknown origin has recently been detected in this region, but it could be associated with processes of disintegration of dark matter particles. “With QUIJOTE we have confirmed the existence of this excess emission and found evidence that said signal could be polarized. This information is essential to understand the nature of this emission”, comments Federica Guidi, a researcher at the Paris Institute of Astrophysics in France.

Finally, the new QUIJOTE maps have made it possible to carry out a systematic study of more than 700 radio and microwave emission sources, both of galactic and extragalactic origin. “For about 40 of these sources in which polarized emission has been detected, the study of their emission properties agrees with the predictions of the models that existed in the literature”, comments Diego Herranz, IFCA researcher.

In addition to these six studies, there are another eight in preparation about to be sent to publish, which continue with the scientific exploitation of the QUIXOTE maps.

QUIJOTE is the result of a scientific collaboration between the IAC, the IFCA, the IDOM company and the University of Cantabria, in Spain, as well as the University of Manchester and the Cavendish Laboratory of Cambridge, in the United Kingdom. (Source: IAC)