Unexpected discovery on the stellar rotation of ultra widespread galaxies

One of the most significant results of the Lewis project is the discovery that Almost half of the UDG examined shows evident signs of rotation in the stars that make them up. This unexpected discovery questioned the current theories on the formation and evolution of these galaxieswhich until now was believed they would not show this type of moti.

“The results we have achieved had a dual satisfaction“, dice Chiara Buttitta, postdoc Inf researcher and first author of one of the two articles published on Astronomy & Astrophysics
. “Not only have we been able to derive the star motions in these extremely weak galaxies, but we found something that we did not expect to observe“.

Artistic representation of an ultra widespread galaxy in the rotation phase. Credits: C. Buttitta/Inif

The spectroscopic analyzes of the Lewis project have revealed that the UDGs are in extremely variable environments and show a surprising variety in their physical properties, such as the kinematic of the stars and the amount of dark matter present.

The observations made it possible to analyze UDG32 in detail, an ultra widespread galaxy located at the end of the filaments of the NGC3314A spiral galaxy. The data collected confirm that UDG32 is associated with the tail of ngc3314a filaments and is not a simple projection effect. In addition, UDG32 shows a stellar population full of metals and intermediate agesuggesting that it may have made up of pre-ray material in the south-east group of the Audra of the Aidra.

Lewis is the first ESO project, led by Inif, entirely dedicated to the study of the UDGs. This program has doubled the number of UDGs analyzed spectroscopically, providing a global vision of their properties within a pile of galaxies still in the formation phase.

“The Lewis project was a challenge. When this program was accepted by the ESO we realized that it was a mine of data to be explored. And such proved to be such“He says Enrichetta Iodice, Inf researcher and scientific manager of the project. “The ‘strength’ of Lewis, thanks to the integral spectroscopy of the used instrument, lies in being able to study simultaneously, for each individual galaxy, not only the motions of the stars, but also the medium stellar population and, therefore, have indications on the training age age and the properties of globular clusters, fundamental tracers also for the content of dark matter. By putting the individual results together, as in a puzzle, the history of formation of these systems is reconstructed“.

Opening image of the NGC3314 and UDG32 galaxies acquired with the Omegacam installed at the VST telescope. Credits: ESO/INF- E. IODICE