The abundance of dwarf galaxies around low-mass giants in the Local
  Volume
  The abundance of satellite dwarf galaxies has long been considered a crucial
test for the current model of cosmology leading to the well-known missing
satellite problem. Recent advances in both simulations and observations have
allowed to study dwarf galaxies around host galaxies in more detail. We have
surveyed a 72 deg2 area of the nearby Sculptor group using the Dark Energy
Camera - also encompassing the two low-mass Local Volume galaxies NGC24 and
NGC45 residing behind the group - to search for hitherto undetected dwarf
galaxies. Apart from the previously known dwarf galaxies we have found only two
new candidates down to a 3 sigma surface brightness detection limit of 27.4 r
mag arcsec-2. Both systems are in projection close to NGC24. However, one of
these candidates could be an ultra-diffuse galaxy associated to a background
galaxy. We compared the number of known dwarf galaxy candidates around NGC24,
NGC45, and five other well-studied low-mass giant galaxies (NGC 1156, NGC2403,
NGC5023, M33, and the LMC) with predictions from cosmological simulations and
found that for the stellar-to-halo mass models considered, the observed
satellite numbers tend to be on the lower end of the expected range. This could
either mean that there is an over-prediction of luminous subhalos in LambdaCDM
or - and more likely - that we are missing some of the satellite members due to
observational biases.
