Astronomers identify 20 ultraviolet-emitting supernova remnants in the Andromeda galaxy

Positions of the 20 SNRs with detected diffuse UV emission (red squares) and the 5 SNRs with probable but unclear diffuse emission (blue squares), superimposed on the Andromeda Galaxy image in the F148W filter. Credit: Leahy et al, 2023 Using the AstroSat satellite, astronomers at the University of Calgary in Canada have identified 20 supernova remnants (SNRs) in the Andromeda galaxy that exhibit diffuse ultraviolet emission. The discovery, presented in a research paper published January 25 on the arXiv preprint server, could help us better understand the origin and properties of ultraviolet emission at SNRs.

SNRs are diffuse, expanding structures that result from a supernova explosion. They contain expanding ejecta from the explosion and other interstellar material that was swept away by the shock wave from the exploding star. Studies of supernova remnants are important for astronomers because they play a fundamental role in the evolution of galaxies, dispersing the heavy elements produced in the supernova explosion and providing the necessary energy to heat the interstellar medium. SNRs are also believed to be responsible for the acceleration of galactic cosmic rays.

Although many extragalactic SNRs have been detected to date, those with ultraviolet (UV) emission are difficult to find, mainly due to the strong interstellar UV extinction of our galaxy. What is noteworthy, despite recent progress in UV-based SNR research, is that a catalog of UV-emitting extragalactic SNRs does not yet exist. That is why a team of astronomers led by Denis Leahy decided to carry out a search for UV-emitting SNRs in the nearby Andromeda Galaxy (also known as Messier 31 or M31), with the aim of generating the first catalog of such objects in another galaxy. . For this purpose, they used AstroSat’s Ultraviolet Imaging Telescope (UVIT).

“The UV images of M31 were obtained by the Ultraviolet Imaging Telescope on the AstroSat satellite, and the SNR list was obtained from the M31 SNR, optical and X-ray catalogs. We used the UVIT images to find SNR with diffuse emission , omitting those heavily contaminated with stellar emission,” the researchers wrote in the paper. The team initially selected 177 SNRs to investigate whether or not they exhibited diffuse ultraviolet emission. Of the entire sample, 20 supernova remnants were found to be UV emitters. The identified sources exhibit diffuse emission that is not associated with stars, although the intensity of the diffuse emission varies.

More information: Denis Leahy et al, Discovery of 20 UV-emitting SNRs in M31 with UVIT, arXiv (2023). DOI: 10.48550/arxiv.2301.10381