Population gradients and photometric metallicities in early- and
  transition-type dwarf galaxies: Clues from the Sculptor group
  We focus on the resolved stellar populations of one early- and four
transition-type dwarf galaxies in the Sculptor group, with the aim to examine
the potential presence of population gradients and place constraints on their
mean metallicities. We use deep HST images to construct CMDs, from which we
select stellar populations that trace different evolutionary phases in order to
constrain their range of ages and metallicities, as well as to examine their
spatial distribution. In addition, we use the resolved stars in the RGB in
order to derive photometric metallicities. All studied dwarfs contain
intermediate-age stars with ages of ~1Gyr and older as traced by the luminous
asymptotic giant branch and red clump stars, while the transition-type dwarfs
contain also stars younger than ~1Gyr as traced by a young main sequence and
vertical red clump stars. Moreover, the spatial distribution of the stars that
trace different evolutionary phases shows a population gradient in all
transition-type dwarfs. The derived error-weighted mean metallicities, assuming
purely old stellar populations, range from -1.5dex for ESO294-G010 to -1.9dex
for Scl-dE1, and should be considered as lower limits to their true
metallicities. Assuming intermediate-age stellar populations to dominate the
dwarfs, we derive upper limits for the metallicities that are 0.3 to 0.2 dex
higher than the metallicities derived assuming purely old populations. We
discuss how photometric metallicity gradients are affected by the
age-metallicity degeneracy, which prevents strong conclusions regarding their
actual presence. Finally, the transition-type dwarfs lie beyond the virial
radius of their closest bright galaxy, as also observed for the LG
transition-type dwarfs. Scl-dE1 is the only dSph in our sample and is an
outlier in a potential morphology-distance relation, similar as the two
isolated dSphs of the LG, Tucana and Cetus.
