Astronomical collaboration maps the structure of our Galaxy’s magnetic field

Almost a decade after starting observations of the sky in the northern hemisphere in the microwave range, the QUIJOTE Collaboration has presented the most accurate description we have of the polarisation of the emission of the Milky Way at these wavelengths.

This is a window of observation not previously explored, which provides complementary information to that obtained previously by space mission (Planck and WMAP) dedicated to the study of the cosmic microwave background radiation (CMB), the fossil radiation left behind by the Big Bang. The new results allow us to obtain information about the structure of the magnetic field of our Galaxy, as well as helping to understand the energetic processes which took place close to the birth of the present Universe.

The QUIJOTE experiment is sited at the Teide Observatory (Izaña, Tenerife) and comprises two telescopes, each of 2.5m diameter which observe the sky in the microwave range (10- 40 GHz). Led by the Instituto de Astrofísica de Canarias (IAC) this experiment started observing in 2012.

Now, thanks to the data obtained with its multifrequency instrument MFI, which was working until 2018, a team of scientists has presented a set of six articles in the specialised journal Monthly Notices of the Royal Astronomical Society (MNRAS) which give the most accurate description until now of the polarisation in the microwave emission processes in our galaxy.

“These maps give a detailed description in a new frequency range, from 10 to 20 GHz, complementary to those from space missions which have previously observed the sky at microwaves, such as Planck (ESA) y WMAP (NASA)”, comments José Alberto Rubiño, the scientist in charge of QUIJOTE, and Principal Investigator of the European project RADIOFOREGROUNDS.

“We have characterised the synchrotron emission from our Galaxy with unprecedented accuracy. This radiation is the result of the emission by charged particles moving at velocities close to that 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.

The CMB is a fossil radiation which originated during the first instants of the universe, and which we observe today at radio wavelength. This type of radiation is studied by scientists because “by studying the properties of its polarisation we hope to find an indirect clue to the existence of gravitational waves after the Big Bang” comments Ricardo Génova-Santos (IAC), a member of the science team.

Manchester started the scientific collaboration with MRAO (Cambridge), IAC (Tenerife) and IFCA (Santander) in the mid 80’s with the Tenerife experiment to study the Cosmic Microwave Experiment from the Spanish Teide Observatory, which went on to create the Very Small Array (VSA), the EU RADIOFOREGROUNDS project and QUIJOTE.

The optical and horn design for QUIJOTE was carried out in Manchester, including local manufacturing work. Manchester apart from providing some of the day-to-day remote observing also helped develop a parallel data processing and mapping pipeline during the commissioning phase. For the final data products, we provided the atmospheric correction and some of assessment of AMI and synchrotron emission.

Dr Robert Watson from The University of Manchester said: “These data will greatly improve our knowledge of the microwave emission mechanisms of our own galaxy which is proving to be messier and more interesting than expected. This will also help in predicting the galactic foreground emission for future higher frequency CMB experiments”.

To measure the signals from the origin of the universe, the scientists need to eliminate the veil of emission associated with our own Galaxy. The new maps provided by QUIJOTE are a tool for performing this task. “One of the most interesting results we have found is that the polarised synchrotron emission from our Galaxy is much more variable than had been thought” comments Elena de la Hoz, a researcher at the Instituto de Física de Cantabria (IFCA). “The results we have obtained are a reference to help future experiments make reliable detections of the cosmological signal” she adds.

The new data from QUIJOTE are also a unique tool for studying the anomalous microwave emission (AME), a type of emission first detected 25 years ago, which is thought to be produced by the rotation of very small particles of dust in the interstellar medium, which tend to be oriented by the presence of the Galactic magnetic field.

Finally, the new maps from QUIJOTE have permitted the systematic study of over 700 sources of emission in radio and microwaves, of both Galactic and extragalactic origin. “For some 40 of these sources in which polarised emission has been detected, study of their properties gives agreement with the predictions of existing models in the literature” comments Diego Herranz, a researcher at IFCA.

QUIJOTE is the result of a scientific Collaboration between the IAC, IFCA, the Department of Engineering and Communications (Santander), the Jodrell Bank Observatory of the University of Manchester, the Cavendish Laboratory (Cambridge) and the IDOM company.

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