The quest for observational evidence of the hierarchical formation process at the smallest galaxy scales

I will present our ongoing project devoted to the search and study of satellites, stellar streams, and substructures around dwarf galaxies. Deep, wide field imaging acquired with the Large Binocular Telescope and follow-up observations performed with the WFC3 on the Hubble Space Telescope provide evidence of multiple satellites associated with the very metal-poor star-forming dwarf galaxy DDO 68. This is a striking example of the few observed cases of hierarchical merging in action at the dwarf galaxy scales. To perform a systematic search of substructures around dwarf galaxies, we have started a Strategic Program at the LBT, named SSH (i.e. The Smallest Scales of Hierarchy Survey) to acquire deep, wide-field imaging of a sample of 45 late-type dwarf galaxies located within 10 Mpc. The survey, which is now close to completion, will provide one of the first systematic observational studies of the hierarchical formation process down to very small galaxy scales. In this talk I will introduce SSH and discuss the results obtained so far.