Andromeda at 6.6 GHz: a unique image of the sister galaxy of the Milky Way


The image obtained at this frequency, in addition to being unprecedented, allowed us to define in detail the morphology of the galaxy and in particular to identify the regions where new stars are born.
The results of the study, a collaboration between Sapienza and the National Institute of Astrophysics, are being published in the journal Astronomy & Astrophysics

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. In fact, the knowledge of the nature of the physical processes that take place inside it, would allow us to better understand what happens in our galaxy, as if we were looking at it from the outside.

Paradoxically, what has so far hampered a deep observation of Andromeda in the microwaves, is its conformation. In fact, 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 frequencies, it is essential to have a single single-dish radio telescope with a large effective area.

A scientific collaboration between Sapienza University of Rome and the National Institute of Astrophysics - INAF, has made it possible to obtain with the Sardinia Radio Telescope a completely new image of the Andromeda galaxy, at 6.6 GHz, a frequency never probed before.
The telescope's excellent angular resolution allowed researchers to study the morphology in detail and to expand the 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 were published in the journal Astronomy & Astrophysics.

At this frequency (6.6 GHz) the galaxy's emission is close to its minimum, complicating the possibility of obtaining such a defined image. Despite this, thanks to 66 hours of observation with the Sardinia Radio Telescope, and a consistent data analysis work, the researchers were able to map the galaxy with high sensitivity.

"The Sardinia Radio Telescope is a large single dish antenna capable of operating at high radio frequencies - underlines Matteo Murgia of the INAF of Cagliari - and of producing data of the highest scientific importance and images of absolute quality".

"By combining this new image with those previously acquired - adds Elia Battistelli of the Department of Physics of Sapienza and coordinator of the study - 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 the formation of new stars, and the fraction of radio signal attributable to non-thermal mechanisms due to cosmic rays that spiral in the magnetic field present in the interstellar medium”, concluded Federico Radiconi of the Physics Department of Sapienza and Sofia Fatigoni of the University of British Columbia.

With the obtained data, it was thus possible for the researchers to estimate the star formation rate within Andromeda, and produce a detailed map that highlighted the disk of the galaxy as the region where new stars born.

In order to obtain this unique image of Andromeda, the team developed and implemented “ad hoc” software that allowed, among other things, to test new algorithms for the identification of lower emission sources in the field of view around Andromeda, the largest never examined at a frequency of 6.6 GHz: in this way the researchers extracted from the map a catalog of about a hundred point sources: stars, galaxies and other objects, on the background of Andromeda.

Image credits:

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 (


S. Fatigoni, F. Radiconi, E.S. Battistelli, M. Murgia, E. Carretti, P. Castangia, R. Concu, P. de Bernardis, J. Fritz, R. Genova-Santos, F. Govoni, F. Guidi, L. Lamagna, S. Masi, A Melis, R. Paladini, FM Perez-Toledo, F. Piacentini, S. Poppi, R. Rebolo, J.A. Rubino-Martin, G. Surcis, A. Tarchi, V. Vacca


Astronomy & Astrophysics (A&A)


Sofia Fatigoni
Department of Physics, Sapienza University of Rome
University of British Columbia

Federico Radiconi
Department of Physics, Sapienza University of Rome

Elia Battistelli
Department of Physics, Sapienza University of Rome

Matteo Murgia
stronomical Observatory of Cagliari, INAF


L' Università degli Studi di Roma "La Sapienza" - Piazzale Aldo Moro 5, 00185 Roma