Survey captures image sequence of galactic neighbors in the local universe

The National Institute for Astrophysics (INAF) has released images of five galaxies in the local universe, taken with the Italian VST ( VLT Survey Telescope) managed by INAF in Chile. The new images show these iconic galaxies in great detail, immortalizing their shape, colors and distribution of stars up to great distances from the center.

Two of them, the irregular galaxy NGC 3109 and the irregular dwarf Sextant A , are located on the edge of the so-called Local Group, which also includes our galaxy, the Milky Way, and are about 4 million light-years away. Two other galaxies, the splendid spiral galaxy known as the Southern Pinwheel (but also NGC 5236 or M 83) and the irregular NGC 5253 are located, respectively, about 15 and 11 million light-years away from ours, while the fifth and most distant, the spiral galaxy IC 5332 , is about 30 million light-years away.

The observations were made in three filters, or colors, as part of the VST-SMASH survey (VST Survey of Mass Assembly and Structural Hierarchy), a project led by Crescenzo Tortora , a researcher at INAF in Naples, to understand the mechanisms that lead to the formation of the many different galaxies that populate the cosmos.

The five galaxies are part of a sample of 27 galaxies that the team is studying with the VST, a telescope with a 2.6-meter diameter mirror, built in Italy and hosted since 2012 at the ESO Observatory on Cerro Paranal, in Chile. These galaxies were carefully selected in the portion of the sky that, over the next few years, will also be observed by the European Space Agency’s Euclid satellite (ESA) to provide a more detailed optical counterpart (up to blue wavelengths) to the space data collected by the VIS instrument (at red wavelengths) and the NISP instrument in the near-infrared.

The group presented the survey in a paper published in The Messenger journal.

“We are trying to understand how galaxies form, as a function of their mass and morphological type. This means asking how stars form in situ, inside galaxies, but also how they are accumulated (ex situ) through merging processes, that is, fusion, with other galaxies” explains Tortora, who leads an international team that involves many researchers from various INAF sites.

“To do this, we need to trace the colors of these galaxies up to the peripheral regions, to be able to investigate the presence of very faint structures belonging to these galaxies, and populations of dim galaxies orbiting around them. This is useful to be able to trace the residues of galactic interactions, and therefore constrain the hierarchical process of cosmic structure formation.”

The analysis of the collected data is still in its early stages, but the observations have already proven effective, allowing the team to examine the galaxies down to very low surface brightnesses, which until a few years ago were difficult to observe.

The VST telescope, with its large field of view of one degree squared, equal to about four times the area of the full moon in the sky, was the key instrument that allowed these images to be made in a relatively short time—observing the field around these galaxies, in the three filters, with 10 hours of observations per degree squared. In comparison, making just one of these images with the Hubble Space Telescope would have required many consecutive exposures.

“This is the first time that all these galaxies have been observed in such a deep and detailed way, and with homogeneous data,” adds Tortora. “In the years to come, only Euclid will reach our optical depths, but it will not be able to count on the vast coverage in the optical lengths of the VST.

“The Vera Rubin Observatory, on the other hand, although observing in spectral regions similar to ours, will reach similar depths only after many years of observation. This makes VST an instrument that can still have its say, and gives hope for interesting results within our survey,” he concludes.