Recent observations of dwarf galaxies have uncovered several tensions with cosmological predictions, such as
an unexpected spatial location around massive galaxies ‑ the plane‑of‑satellite problem ‑, a discrepant dark matter
content, and a higher than expected population of globular clusters. They add to other known problems
and challenge the otherwise highly successful Λ + Cold Dark Matter (ΛCDM) model of cosmology.

Unfortunately, the detailed studies of dwarf galaxies are hampered by their low luminosities and low surface‑brightness
and have so far been limited to a few nearby galaxy groups, including our own Local Group.
Using the Canada‑France‑Hawaii Telescope we observed over 200 fields around giant galaxies to an extremely
deep surface brightness limit. With this data set, we identified an unprecedented number of 2210 dwarf galaxies.
As follow‑up programs, we were granted 87 orbits with the HST in cycle 28 (Oct. 2020 ‑ Sep. 2021) for a
subsample of these dwarf galaxies, which represents the largest systematic study of dwarf galaxies with HST
to date. This data set will be accompanied with up to 99 hours of observation time from MUSE mounted at
the VLT, as part of a snapshot program (Oct. 2020 ‑ Apr. 2021). With this data set we will answer some pressing
questions posed in our field of research: Is there a population of dark matter‑deficient dwarf galaxies with
extreme globular cluster systems? Do the properties of dwarf galaxies vary with their environment? Is there
more evidence for co‑rotating planes of dwarf galaxies? This new data will increase the study of these objects
from a few to a statistically meaningful sample and will test if these challenges to our cosmological model will
remain or vanish.

Our multi‑disciplinary team consists of researchers based in Europe (France, Austria, Netherlands, UK), the
USA, South Africa, and South Korea. At the ISSI in Bern, we aim to bring our team together for the first time
face‑to‑face for two one‑week meetings. Our first planned ISSI meeting will focus on the scientific questions
regarding nearby dwarf galaxies, with a focus on the new HST and VLT data acquired in 2020/21. The second
meeting will enlarge the discussions around next-generation surveys, in particular, those to be carried out in
the near future with Space missions such as Euclid. It will provide the opportunity to use the experience gained
from our ground and space‑based observations to adjust our strategy to exploit the new surveys and detect
their dwarf galaxies and globular cluster populations.

With our project and proposed meetings at ISSI, we aim to get a deeper understanding of dwarf galaxies, combining
a statistically significant sample of observed dwarf galaxies and their globular clusters with expertise in
galaxy formation and cosmological simulations.