The Smallest Scale of Hierarchy Survey (SSH). I. Survey Description

The Smallest Scale of Hierarchy (SSH) survey is an ongoing strategic large program at theLarge Binocular Telescope, aimed at the detection of faint stellar streams and satellites around45 late-type dwarf galaxies located in the Local Universe within10 Mpc.SSH exploits thewide-field, deep photometry provided by the Large Binocular Cameras in the two wide filtersgandr. This paper describes the survey, its goals, and the observational and data reductionstrategies. We present preliminary scientific results for five representative cases (UGC 12613,NGC 2366, UGC 685, NGC 5477, and UGC 4426) covering the whole distance range spannedby the SSH targets. We reach a surface brightness (SB) limit as faint asμ(r)∼31 mag arcsec−2both for targets closer than 4–5 Mpc, which are resolved into individual stars, and for moredistant targets through the diffuse light. Our analysis reveals the presence of extended low SBstellar envelopes around the dwarfs, reaching farther out than what traced by the integratedlight, and as far out as, or even beyond, the observed HIdisc. Stellar streams, arcs, and peculiarfeatures are detected in some cases, indicating possible perturbation, accretion, or mergingevents. We also report on the discovery of an extreme case of Ultra Diffuse Galaxy (μg(0)=27.9 mag arcsec−2) in the background of one of our targets, to illustrate the power of the surveyin revealing extremely low SB systems