The HST/ACS Coma Cluster Survey: VII - Colour Gradients in Giant and
  Dwarf Early-Type Galaxies
  Using deep, high-spatial resolution imaging from the HST ACS Coma Cluster
Treasury Survey, we determine colour profiles of early-type galaxies in the
Coma cluster. From 176 galaxies brighter than $M_\mathrm{F814W(AB)} = -15$ mag
that are either spectroscopically confirmed members of Coma or identified by
eye as likely members from their low surface brightness, data are provided for
142 early-type galaxies. Typically, colour profiles are linear against
$\log(R)$, sometimes with a nuclear region of distinct, often bluer colour
associated with nuclear clusters. Colour gradients are determined for the
regions outside the nuclear components. We find that almost all colour
gradients are negative, both for elliptical and lenticular galaxies. Most
likely, earlier studies that report positive colour gradients in dwarf galaxies
are affected by the bluer colours of the nuclear clusters, underlining that
high resolution data are essential to disentangle the colour properties of the
different morphological components in galaxies. Colour gradients of dwarf
galaxies form a continuous sequence with those of elliptical galaxies, becoming
shallower toward fainter magnitudes. Interpreting the colours as metallicity
tracers, our data suggest that dwarfs as well as giant early-type galaxies in
the Coma cluster are less metal rich in their outer parts. We do not find
evidence for environmental influence on the gradients, although we note that
most of our galaxies are found in the central regions of the cluster. For a
subset of galaxies with known morphological types, S0 galaxies have less steep
gradients than elliptical galaxies.
