Using the Sardinia Radio Telescope, a 64-m fully steerable radio telescope near San Basilio, Sardinia, Italy, an international team of astronomers has produced a detailed radio image of the Andromeda — the best-known large galaxy besides our own Milky Way — at the microwave frequency of 6.6 GHz.
An image of the Andromeda Galaxy from the Sardinia Radio Telescope after averaging over the whole bandwidth at 6.6 GHz. Image credit: Fatigoni et al., doi: 10.1051/0004-6361/202040011.
The Andromeda Galaxy is the largest galaxy of the Local Group, which includes the Milky Way, the Triangulum galaxy (Messier 33), and several other smaller galaxies including the satellite Messier 32 and Messier 110.
Also known as Messier 31 or M31, it is a large disk galaxy at a distance of 2.5 million light-years from Earth, and has a proper redshift of z=-0.001, where the negative value shows that it is moving towards the Milky Way.
Because of its size and distance in the sky, the Andromeda Galaxy is an excellent laboratory with which to further study and perhaps confirm the physical mechanisms and properties that have so far only been studied in detail in our own Galaxy.
It also provides information about the general features of a typical disk galaxy.
“The new image from the Sardinia Radio Telescope will allow us to study the structure of Andromeda and its content in more detail than has ever been possible,” said Sofia Fatigoni, a Ph.D. student in the Department of Physics and Astronomy at the University of British Columbia.
“Understanding the nature of physical processes that take place inside Andromeda allows us to understand what happens in our own Milky Way Galaxy more clearly — as if we were looking at ourselves from the outside.”
Prior to this study, no maps capturing such a large region of the sky around the Andromeda Galaxy had ever been made in the microwave band frequencies between one GHz to 22 GHz.
In this range, the galaxy’s emission is very faint, making it hard to see its structure.
However, it is only in this frequency range that particular features are visible, so having a map at this particular frequency is crucial to understanding which physical processes are happening inside the Andromeda.
“By combining this new image with those previously acquired, we have made significant steps forward in clarifying the nature of Andromeda’s microwave emissions and allowing us to distinguish physical processes that occur in different regions of the galaxy,” said Professor Elia Battistelli, an astronomer in the Physics Department at the Sapienza University of Rome, INFN-Sezione di Roma, and INAF-Osservatorio Astronomico di Cagliari.
For the study, the astronomers developed and implemented new software to identify never-before-examined lower emission sources in the field of view around Andromeda at a frequency of 6.6 GHz.
From the resulting map, they were able to identify a catalog of about 100 point sources, including stars, galaxies and other objects in the background of Andromeda.
They also calculated a map of the star formation rate in the galaxy. Integrating within a radius of 49,000 light-years, they obtained a total star formation rate of 0.19 solar masses per year — which is in agreement with previous results in the literature.
“We were able to determine the fraction of emissions due to thermal processes related to the early stations of new star formation, and the fraction of radio signals attributable to non-thermal mechanisms due to cosmic rays that spiral in the magnetic field present in the interstellar medium,” Fatigoni said.
The team’s results were published in the journal Astronomy & Astrophysics.
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S. Fatigoni et al. 2021. Study of the thermal and nonthermal emission components in M 31: the Sardinia Radio Telescope view at 6.6 GHz. A&A 651, A98; doi: 10.1051/0004-6361/202040011
