Location of HST ACS (red squares) and WFC3 (purple squares) fields overlaid on a deep 75′ × 75′ g-band image provided by the DNGS (Abraham & van Dokkum 2014). North is up and east is to the left. High surface brightness regions of the g-band image are replaced by the color image from the SDSS. The white and black dashed lines represent circles with (24 kpc) and 25′ (48 kpc) radii centered on M 101, respectively. A black contour line indicates a smoothed iso-surface brightness level of μ_g = 30 mag arcsec⁻² measured in this study.