Nearly 50 'ghost galaxies' emerge around three hosts, challenging dwarf galaxy counts

Nearly 50 dwarf galaxies were discovered around three host galaxies—NGC 5068, NGC 5084, and NGC 5087—located 17, 80, and 100 million light-years away, respectively. The findings, obtained through observations from the VST (VLT Survey Telescope), reveal these galaxies as "ghost galaxies" that are extremely faint and difficult to detect. The results, published in Astronomy & Astrophysics, indicate that these galaxies are likely satellites of the larger host galaxies and are distributed in a plane similar to the Milky Way's satellites. The study shows that the spatial distribution of these galaxies challenges current understanding of galaxy formation and evolution.

The research team conducted a meticulous visual inspection of the images, using a technique that avoids automated algorithms and instead relies on human observation. They identified 47 candidate dwarf galaxies, of which four were previously known. The newly discovered galaxies are diffuse, low surface brightness, and lack internal structures, with masses between one million and one billion solar masses. The study highlights that these galaxies' light profiles are not steep, similar to disk galaxies, and their color changes with distance from the center, consistent with most galaxies in the universe.

The findings challenge the standard cosmological model's predictions about the number and distribution of dwarf galaxies. The results suggest that the "missing satellite galaxies" problem may not be confined to the Local Group and that the observed number of satellite galaxies could be higher than simulations predict. The study also emphasizes the importance of deep optical images and the need for further spectroscopic observations to confirm the nature and properties of these galaxies. The VST-SMASH survey is part of a larger effort to extend the search for dwarf galaxies using the Euclid space telescope.

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