An article published in the journal “Astronomy & Astrophysics” reports a study on the Andromeda galaxy based on the best image captured in the microwave band. A team of researchers coordinated by Professor Elia Battistelli of the physics department at Sapienza used the Sardinia Radio Telescope (SRT) and its ability to work at high radio frequencies to create a map of Andromeda at 6.6 GHz, a frequency detected for the first time that fills a gap in the studies of the galaxy considered a sort of sister of the Milky Way. This helped to better understand the processes taking place within Andromeda identifying areas of star formation.
Many different instruments have been used to capture emissions from the Andromeda galaxy in the various bands of the electromagnetic spectrum but not at microwaves between 1 GHz and 22 GHz. This was due to the fact that the emissions at those frequencies are very weak and this made it difficult to see its structure. To obtain useful detections, astronomers needed a suitable instrument: powerful radio telescopes made up of many small antennas have problems observing relatively large objects while the Sardinia Radio Telescope proved to be perfect for this job.
The single 64-meter, fully steerable antenna with a large effective area of the Sardinia Radio Telescope is capable of operating at high radio frequencies. This was crucial for this study but it still took 66 hours of observations to obtain a microwave map of the Andromeda galaxy with the necessary details for subsequent analysis.
New software was developed to identify lower-emission sources in the field of view around the Andromeda galaxy at a frequency of 6.6 GHz. The end result was a catalog of about one hundred point sources including stars, galaxies, and other objects in the background of Andromeda.
The top image (Courtesy S. Fatigoni et al (2021). All rights reserved) shows Andromeda seen from the Sardinia Radio Telescope at 6.6 GHz. The bottom image (Radio: Wsrt/R. Braun; Microwave: Srt/S.Fatigoni et al.; Infrared: Nasa/Spitzer/K. Gordon; Visible: Robert Gendler; Ultraviolet: Nasa/Galex; X-ray: ESA/Xmm/W. Pietsch) shows Andromeda in various bands of the electromagnetic spectrum with the 6.6 GHz one filling the gap.
This new microwave study of the Andromeda galaxy is not separate from the previous ones based on observations in other bands of the electromagnetic spectrum. On the contrary, the new observations were combined with previous ones allowing to identify the nature of various microwave emissions distinguishing different physical processes taking place in different regions of Andromeda.
One of the important results was the determination of the part of emissions generated by thermal processes connected to the first phase of the formation of new stars and of the part generated by non-thermal processes connected to cosmic rays in the magnetic field present in the interstellar medium.
The Andromeda galaxy is considered a kind of sister to the Milky Way due to its relative proximity and because the two galaxies have a similar structure. The study of star formation processes remains among the most important in the field of astronomy and studying it in Andromeda also offers clues to what happens in the Milky Way. For this reason, this study of Andromeda has various important ramifications that can have more future developments.
