We request g- and i-band HSC imaging to complete the mapping of a large Milky Way-like galaxy NGC 253 (M* ∼ 1011M⊙) and a lower-mass disk galaxy NGC 4244 (M* ∼ 109.5M⊙), which lie at 3.5 Mpc and 4.4 Mpc. In the archival data of these two galaxies, three substructures are discovered at the edges of the current coverages. Motivated by these exciting discoveries and the potential return of complete mapping of the stellar halos of these systems, we request an additional dataset. We will: [1] Fully map and characterize the properties (e.g. stellar content, structures, luminosities) of the new substructures and search for further examples of these features in unexplored regions. [2] Search for new dwarf satellites that will provide further information on accretion histories, and will enable unprecedented studies of satellite systems beyond the Local Group. [3] Quantify the stellar halo properties. We will analyze the radial profile, 2D shape, stellar mass, and metallicity of the stellar halos and compare them to those of the Milky Way and M31, as well as simulation predictions. [4] Search for halo globular clusters. Using luminosity, color, and sizes of known GCs on images as well as ancillary data at other wavelengths, we will define criteria for selecting GC candidates around each galaxy.
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