NGC 474 as viewed with KCWI: diagnosing a shell galaxy
  We present new spectra obtained using Keck/KCWI and perform kinematics and
stellar population analyses of the shell galaxy NGC 474, from both the galaxy
centre and a region from the outer shell. We show that both regions have
similarly extended star formation histories although with different stellar
population properties. The central region of NGC 474 is dominated by
intermediate-aged stars (8.3 \pm 0.3 Gyr) with subsolar metallicity ([Z/H]=
-0.24 \pm 0.07 dex) while the observed shell region, which hosts a substantial
population of younger stars, has a mean luminosity-weighted age of 4.0 \pm 0.5
Gyr with solar metallicities ([Z/H]=-0.03 \pm 0.09 dex). Our results are
consistent with a scenario in which NGC 474 experienced a major to intermediate
merger with a log\((M_*/M_\odot)\sim10 \) mass satellite galaxy at least \sim 2
Gyr ago which produced its shell system. This work shows that the direct
spectroscopic study of low-surface brightness stellar features, such as shells,
is now feasible and opens up a new window to understanding galaxy formation and
evolution.
