An image composed of data collected by the DECam (Dark Energy Camera) shows a group of spiral galaxies with NGC 1515 in the center. It’s a galaxy considered part of the so-called Dorado Group, a set of galaxies with gravitational bonds that are not numerous enough to be defined as a galaxy cluster. Other spiral galaxies included in the image are at various distances from Earth and the farthest are indistinguishable to the naked eye from Milky Way stars present in that area of the sky.
The Dorado Group contains enough galaxies to merit a division into subgroups defined around the galaxies NGC 1672, NGC 1566, and NGC 1433. NGC 1515 is part of the subgroup of NGC 1566, a galaxy considered very interesting also for its active galactic nucleus powered by a supermassive black hole.
Over time, various galaxies have been added to the Dorado Group and in some cases, there have been discussions regarding their membership in this group. It can take years to assess the movements of one galaxy relative to others accurately enough to understand if there’s a gravitational bond. That’s why the discussions also concerned whether it fell under the definition of a group or a cluster.
Installed at the Cerro Tololo Inter-American Observatory (CTIO), Chile, the DECam is an instrument designed primarily for cosmological studies. Between 2013 and 2019 it was used for the Dark Energy Survey (DES), an investigation focused on the expansion of the universe that aims to provide useful information to understand the mystery of dark energy, the working hypothesis created to explain the acceleration in the universe expansion. During this investigation, DECam captured an enormous amount of images that can be useful for many different types of astronomical studies.
This image (Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA. Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)) is one of many examples of the results of DECam’s work. In this case, mainly spiral galaxies with NGC 1515 in particular prominence are portrayed at optical frequencies. It’s only a very small portion of the sky which, however, gives an idea of the immense quantity of objects present in the universe.
