Andromeda is one of the most studied galaxies of all time and probably also the best known to the general public for its proximity and similarity to our own galaxy, the Milky Way. Knowing the nature of the physical processes inside it would allow us to better understand what happens in our galaxy as if we were looking at it from the outside.

Paradoxically, the very thing that has so far hindered an in-depth microwave observation of Andromeda is its very conformation. Due to its proximity to the Milky Way, it has an angular dimension of several degrees in the sky, which puts it out of the reach of interferometers made up of small antenna arrays. In order to observe Andromeda at frequencies of 6.6 GHz and higher, it is essential to have a single-dish radio telescope with a large effective area.

Today, a scientific collaboration between Sapienza University of Rome and the National Institute of Astrophysics (INAF) has made it possible to obtain a completely new image of the Andromeda galaxy with the Sardinia Radio Telescope, at 6.6 GHz, a frequency never explored before.

The telescope's excellent angular resolution allowed the researchers to study the morphology in detail and thus expand astrophysical information on this galaxy.

The results of the study carried out with the participation of numerous international institutions and universities such as the University of British Columbia, the Instituto de Radioastronomia y Astrophysics - UNAM in Mexico, the Instituto de Astrofisica de Canarias, the Infrared Processing Analysis Center - IPAC in California have been published in the journal Astronomy & Astrophysics.

At this frequency (6.6 GHz), the galaxy's emission is close to its minimum, making it difficult to obtain such a defined image. Nevertheless, thanks to 66 hours of observation with the Sardinia Radio Telescope, and substantial data analysis work, the researchers could map the galaxy with high sensitivity.

"By combining this new image with those previously acquired" -says Elia Battistelli of the Department of Physics of Sapienza and study coordinator - "we have made significant steps forward in clarifying the nature of the Andromeda microwave emission, distinguishing the physical processes that occur in different regions of the galaxy."

"In particular, we were able to determine the fraction of emission due to thermal processes related to the early stages of new star formation, and the fraction of radio signal attributable to non-thermal mechanisms due to cosmic rays spiralling in the magnetic field present in the interstellar medium," concluded Federico Radiconi of the Department of Physics of Sapienza and Sofia Fatigoni of the University of British Columbia.

With the obtained data, the researchers estimated the star formation rate within Andromeda and produced a detailed map highlighting the disk of the galaxy as the region where new stars are born.

To obtain this unique image of Andromeda, the team developed and implemented "ad hoc" software that allowed them, among other things, to test new algorithms for the identification of lower emission sources in the field of view around Andromeda, the largest ever examined at a frequency of 6.6 GHz. In this way, the researchers extracted from the map a catalogue of about a hundred point sources, i.e. stars, galaxies and other objects, in the background of Andromeda.

References:

Study of the thermal and non-thermal emission components in M31: the Sardinia Radio Telescope view at 6.6 GHz - Sofia Fatigoni, Federico Radiconi, Elia Stefano Battistelli, Mauro Murgia, Ettore Carretti, Paola Castangia, Raimondo Concu, Paolo de Bernardis, Jacopo Fritz, Ricardo Genova-Santos, Federica Govoni, Federica Guidi, Luca Lamagna, Silvia Masi, Andrea Melis, Roberta Paladini, Fabricio Manuel Perez-Toledo, Francesco Piacentini, Sergio Poppi, Rafael Rebolo, Jose Alberto Rubino-Martin, Gabriele Surcis, Andrea Tarchi, Valentina Vacca - Astronomy & Astrophysics 2021 https://doi.org/10.1051/0004-6361/202040011

Further Information

Elia Battistelli 
Department of Physics 
elia.battistelli@uniroma1.it