Monday

The existence of large numbers of ultra-diffuse galaxies, an hitherto unknown
type of galaxies, is arguably one of the major discoveries in extragalactic
astronomy made over the past few years. This ubiquitous new population of
galaxies constitutes a major challenge to our current understanding
of galaxy formation and evolution. Low surface brightness imaging has also
discovered a wealth of structures around galaxies, which possibly
are the remnants and signatures of hierarchical galaxy formation.
These discoveries, among others, arise thanks to both new instrumentation
designed to explore the ultra-low surface brightness universe, and to new
ways to analyse images on large telescopes, pushing to extreme limits what
can be achieved in the very challenging detection of extended objects whose
brightness is a tiny fraction of the sky background. The review will describe the current state of the subject at all wavelengths considered (UV/optical/IR/radio)
as well as and new ground- and space-based projects aimed at mapping the
sky at unprecedented deep surface brightness limits.