Quartet Of Galaxies For the Vst (Cosmology)

It comes from a study led by Rossella Ragusa of INAF of Naples, published in Astronomy & Astrophysics, the image of the week of the European Southern Observatory. This is the group of Hcg 86 galaxies immortalized by the Vlt Survey Telescope, an instrument also “made in Naples”

Space can be a lonely place. But not so for the quartet of galaxies that make up Hcg 86 , which can be seen in the image on the right observed with the VLT Survey Telescope ( VST ) ESO. The four galaxies, located approximately 270 million light-years from Earth in the constellation Sagittarius, are seen from Earth as arranged in a triangular shape, with three of them in a straight line and one to the south (the bright objects to the right of the group are not part of the quartet).

The acronym ‘Hcg’ stands for Hickson Compact Group , and is used to describe groups composed of a minimum of four up to a maximum of ten galaxies physically very close to each other. Because of their compactness, such groups are ideal environments for studying galactic interactions, which can sometimes lead to the merger of their members.

“With Vst we are able to investigate very weak structures in the periphery of galaxies, which are the remains of past gravitational interactions and fusion events”, explains the INAF researcher from Naples and the Federico II University Rossella Ragusa , at the helm of the team that – as part of the Vst Early-type Galaxy Survey ( Vegas ) program – obtained the image of Hcg 86. “In fact, as in the case of Hcg 86, revealing the distribution of diffused light within the group, or the weakest member of the group, and by studying its physical properties, we are able to add fundamental elements in the knowledge we have of the history of formation and evolution of cosmic structures ».

Rossella Ragusa, researcher at the Capodimonte Astronomical Observatory of INAF and at the University of Naples Federico II, first author of the study on the group of galaxies Hcg 86 © INAF

«These images are among the deepest obtained by the Vegas survey and have been reduced with the AstroWise pipeline , developed for the data reduction of the Vst telescope. The pipeline has also proved to be very effective for the detection and study of low surface brightness structures, such as those involved in the work on the Hcg 86 group », adds Marilena Spavone of  INAF of Naples, responsible for data reduction. Specifically, by mapping the distribution of light in and around the galaxies of HCG 86, the team concluded that these faint structures are the remnants of the satellite galaxies devoured by the group about seven billion years ago.

Located at the ESO Observatory in Paranal, Chile, the Vst is one of the largest survey telescopes in the world, dedicated to mapping the sky into the wavelengths of visible light. 2021 marks the anniversary of its first decade of activity , a period during which it achieved significant scientific results in the search for extra-solar planets and in the study not only of our galaxy but of the wider universe.

Featured image: The group of galaxies Hcg 86 immortalized by Vst. Credits: Eso / Ragusa, Spavone et al.

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Provided by INAF

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