Astronomers discover a new nearly dark galaxy

A region of 100′′×100′′ around Nube. The figure is a composite of an RGB color image using the g, r and i HiPERCAM bands and a black and white g + r image for the background. Credit: arXiv (2023). DOI: 10.48550/arxiv.2310.12231

It is 10 times fainter than typical ultra-diffuse galaxies. While analyzing deep optical images from the IAC Stripe 82 Legacy project, an international team of astronomers accidentally discovered a new near-dark galaxy. The galaxy, called Nube, has a very low surface brightness and is as massive as the Small Magellanic Cloud (SMC). This was reported by Such dark galaxies have no obvious optical counterparts and are often overlooked in the optical catalogs of large-scale studies. However, upon further exploration, these faint galaxies can have extremely weak optical emissions. A team of astronomers from the University of La Laguna in Spain has discovered another galaxy of this rare type. They identified it during a visual inspection of one of the survey areas of the IAC Stripe 82 Legacy project, a comprehensive study of low surface brightness astronomy.

Nube is located 350 million light years from Earth. The galaxy is estimated to be 10 billion years old and its metallicity (the concentration of elements heavier than hydrogen and helium in stars or other astronomical objects) is estimated to be −1.1. As for Nube’s other basic parameters, they are very wide, with a half-mass radius of 22,500 light-years. This galaxy has a stellar mass of approximately 390 million solar masses and its total halo mass is estimated at 26 billion solar masses. Based on the results obtained, the authors of the paper came to the conclusion that Nube is the largest and most extensive galaxy of its type discovered to date. The galaxy is also 10 times fainter and its radius is three times larger than typical ultra-diffuse galaxies of similar stellar mass.

Ultra-diffuse galaxies are galaxies with extremely low density and size, comparable to the Milky Way. But they contain only 1% more stars than our galaxy. Given the extreme properties of Nube, researchers are studying the origin and nature of this galaxy. Scientists want to know whether these properties are a result of the galaxy’s initial formation or whether they are due to later evolution caused by the environment in which it resides. Scientists also studied the distribution of stars in Nouba to see if it matched the distribution of dark matter. It turns out that the shape of the distribution of stars matches the typical shape of the dark and faint mother. This confirms the possibility of using the distribution of stars in the galaxy to estimate the distribution of dark matter in its halo.