The abundance of dwarf galaxies around low-mass giants in the Local Volume

TL;DR

This study surveys dwarf galaxies around low-mass giants in the Local Volume, finding fewer satellites than predicted by cosmological models, which suggests potential observational biases or over-predictions in simulations.

Contribution

It provides new observational data on dwarf galaxy abundance around low-mass hosts and compares these with cosmological predictions, highlighting discrepancies.

Findings

Only two new dwarf candidates found near NGC24.

Observed satellite numbers are lower than model predictions.

Possible observational biases or over-predictions in simulations.

Abstract

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.