We propose a systematic study of Ultra Diffuse Galaxies (UDGs) in very nearby massive clusters, compiling different mass and dynamical states, using deep HSC images in g and i bands. The unique population of UDGs has emerged into a serious problem that confronts the standard picture of structural formation and galaxy evolution in dense environment. To understand UDGs, we aim to: (1) accurately model their photometric structure, and extract color information; (2) compare their number density, spatial distribution, and key properties among different clusters to shed light on their relation to the evolution of their host clusters, especially on how can they survive this harsh environment; (3) compare their structures with other populations of dwarf galaxies in the cluster, and other low surface brightness galaxies in the field, to explore possible evolutionary connection. We advocate that observation like this can help HSC make a mark in this emerging topic.
Despite their potential large number density and importance in verifying galaxy formation theory under \(\Lambda\)-cold dark matter (\(\Lambda\)-CDM) cosmology, the Low Surface Brightness (LSB) galaxies are still largely unexplored even in the low redshift universe. Early this year, the Dragonfly camera array uncovered a population of large and diffuse dwarf galaxies (referred as Ultra Diffuse Galaxies, or UDGs) within the virial radius of the Coma cluster at \(z=0.023\) (Dokkum 2015). These UDGs have the typical luminosity of a dwarf elliptical galaxy, yet their effective radius can be as large as our Milky Way. These are very surprising discoveries not only because they populate a parameter space that was occupied by very few galaxies (see Fi