Low surface brightness galactic stellar halos provide a challenging but promising path towards unraveling the past assembly histories of individual galaxies .
Here , we present detailed comparisons between the stellar halos of Milky Way-mass disk galaxies observed as part of the Dragonfly Nearby Galaxies Survey ( DNGS ) and stellar mass-matched galaxies in the TNG100 run of the IllustrisTNG project .
We produce stellar mass maps as well as mock g and r -band images for randomly oriented simulated galaxies , convolving the latter with the Dragonfly PSF and taking care to match the background noise , surface brightness limits and spatial resolution of DNGS .
We measure azimuthally averaged stellar mass density and surface brightness profiles , and find that the DNGS galaxies generally have less stellar mass ( or light ) at large radii ( > 20 kpc ) compared to their mass-matched TNG100 counterparts , and that simulated galaxies with similar surface density profiles tend to have low accreted mass fractions for their stellar mass .
We explore potential solutions to this apparent `` missing outskirts problem '' by implementing several ad-hoc adjustments within TNG100 at the stellar particle level .
Although we are unable to identify any single adjustment that fully reconciles the differences between the observed and simulated galaxy outskirts , we find that artificially delaying the disruption of satellite galaxies and reducing the spatial extent of in-situ stellar populations result in improved matches between the outer profile shapes and stellar halo masses , respectively .
Further insight can be achieved with higher resolution simulations that are able to better resolve satellite accretion , and with larger samples of observed galaxies .