(Proposal ID) S17A-021

(PI) Koda, Jin

(Proposal Title)
Environmental dependence of ultra diffuse galaxies (UDGs) with HSC

(Abstract)
The recently-discovered ultra-diffuse galaxies (UDGs) in the Coma cluster are 
promising candidates for dark galaxies that consist dominantly of dark matter. 
Their preferred presence in dense cluster environment has been only inferred 
from scarce circumstantial evidence, and their nature, origin, and properties 
have remained mostly unknown. Here we propose a systematic census of the UDG 
population in {all} 6 nearby (z<0.03) galaxy clusters observable in S17A, 
covering a range of cluster internal velocity dispersion (equivalently mass, 
density, and richness). We have obtained the deep HSC r-band imaging of the 6 
clusters {out to their virial radii} in S16A, but the time for HSC g-band was 
weathered out. We therefore request 3 nights for the g-band imaging of the 6 
clusters, exploring the variation of UDG colors with cluster-centric radius. 
Several mechanisms have been suggested for the formation of UDGs in clusters, 
including gas removal from their dark halos by ram-pressure stripping, galaxy 
harassment, and galactic winds triggered by interaction-driven starbursts. 
The impacts of these mechanisms depend on cluster richness and UDGs' radial 
locations within clusters. The impacts should appear in the shapes and stellar 
populations (integrated colors and color profiles) of the UDGs.