A prediction of the ΛCDM framework for structure formation is that present-day galaxies should be surrounded by vast stellar envelopes that are composed of the remnants of now-devoured small satellites. It is therefore surprising that a recent deep integrated light survey of a modest sample of nearby galaxies with the Dragonfly array finds that almost half of them possess no discernible stellar halo. In 20A, we were awarded 2.6n of HSC time to map the resolved red giant branch (RGB) stars in the outskirts of M101, which at D∼7 Mpc is the closest of these peculiar systems. Although our proposal was highly-ranked and awarded carryover status, it achieved only ≈50% completion and most of the data taken were in a single filter (i2), prohibiting the detection of the bulk of the RGB stars. We request time here to obtain the missing data for our program and thus realise our original goals. By detecting RGB stars to >∼1.5 magnitudes below the RGB tip to radii of ∼ 80 kpc and µV ∼33−34 mag arcsec−2, we will improve significantly on the Dragonfly stellar halo limits. We will also conduct a crucial consistency check of the integrated light and resolved star approaches for mapping extremely low surface brightness emission around galaxies.
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