S20A0114abst
S20A0114
A generic 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. We propose here to use HSC to map resolved red giant branch (RGB) stars in the outskirts of M101, which at D∼6.5 Mpc is the closest of these peculiar systems, and to use this information to place new limits on the contribution and properties of any stellar halo component. Our deep photometry will detect RGB stars to ∼1.5 magnitudes below the RGB tip and enable a search for M101’s stellar halo to be extended to radii of ∼ 80 kpc and µV ∼32−33 mag arcsec−2, numbers which improve significantly on the Dragonfly limits. Furthermore, the mean metallicity and metallicity distribution of any putative halo can be inferred from the colours of the detected RGB stars. Crucially, our observations will provide a critical consistency check of the integrated light and resolved star approaches for mapping extremely low surface brightness emission in and around galaxies.
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