A too-many-dwarf-galaxy-satellites problem in the M 83 group

Dwarf galaxies in groups of galaxies provide excellent test cases for models of structure formation. This led to a so-called small-scale crisis, including the famous missing-satellites and too-big-to-fail problems. It was suggested that these two problems can be resolved by introducing baryonic physics to cosmological simulations. We tested the nearby grand spiral M 83 - a Milky Way sibling - to determine whether its number of dwarf galaxy companions is compatible with today's Λ cold dark matter model using two methods: with cosmological simulations that include baryons and with theoretical predictions from the subhalo mass function. By employing distance measurements, we recovered a list of confirmed dwarf galaxies within 330 kpc of M 83 down to a magnitude of M_V = −10. We find that both the state-of-the-art hydrodynamical cosmological simulation Illustris-TNG50 and theoretical predictions agree with the number of confirmed satellites around M 83 at the bright end of the luminosity function (> 10⁸ solar masses) but underestimate it at the faint end (down to 10⁶ solar masses) at more than 3σ and 5σ levels, respectively. This indicates a too-many-satellites problem for M 83 in the Λ cold dark matter model. The actual degree of tension with cosmological models is underestimated because the number of observed satellites is incomplete due to the high contamination of spurious stars and Galactic cirrus.