An article accepted for publication in “The Astrophysical Journal” describes the VST Early-type GAlaxy Survey (VEGAS). A team of researchers led by Marilena Spavone from INAF-Astronomical Observatory of Capodimonte in Naples, Italy, used ESO’s VLT Survey Telescope (VST) in Chile to obtain highly detailed images of many elliptical galaxies. Among them there’s NGC 5018, interesting among other things for structures such as what’s called a tidal tail, a stream of gas containing various stars stretching outwards from that galaxy. These are evidence of interactions between galaxies that provide information on the characteristics of primordial galaxies.
Just over 130 million light years from Earth, the galaxy NGC 5018 is the brightest of a small group of five galaxies. The top image (ESO/Spavone et al.) shows the area of the sky around NGC 5018, the bottom image (ESO/Spavone et al.) is an annotated version that indicate some of the objects that were photographed.
The most interesting feature of NGC 5018 is its tidal tail that joins it to a nearby galaxy, NGC 5022. It’s the result of an interaction between the two galaxies: in the past, at some point they got so close to each other that the gravity force of NGC 5022 managed to snatch gas from its neighbor, creating a bridge between them. Gravitational stress compressed the gas in various areas of the tail causing the formation of stars inside it. Another structure exists between NGC 5022 and another small spiral galaxy of the group called MCG-03-34-013, close to the center of the image but not indicated in the annotated version.
Thanks to the OmegaCAM instrument installed on the VST the researchers managed to capture the details of the examined galaxies and structures such as the tidal tail of NGC 5018, not visible to an examination conducted with less sensitive instruments. In the observations that generated an image that in its maximum resolution reaches 400 megapixels, there was a sort of photobombing caused by objects between the Earth and NGC 5018’s group.
The result is that near the central area of the image, north-west of the galaxy NGC 5018, there’s a star that looks very bright, HD 114746. Even a couple of asteroids ended up in the image: 2001 TJ21 (110423) just below the galaxies NGC 5018 and NGC 5022 and 2000 WU69 (98603) to their right. These objects are not part of this research, but information were collected about them and many others that could be useful to other researchers.
In the research on galaxy interactions, the possibility of examining structures that show their signs allows to reconstruct their history. Close passages and even galaxy mergers marked the history of NGC 5018 and its neighbors, events that are common but crucial for their evolution and consequently on star formation within them. This research is focused on elliptical galaxies but the results can also be valuable for other types of galaxies such as the Milky Way.