We studied the stellar populations of 40 early-type galaxies using medium resolution long-slit spectroscopy along their major axes ( and along the minor axis for two of them ) .
The sample , including elliptical and lenticular galaxies as well as dwarf galaxies , is combined with other previously published data in order to discuss the systematics of the radial gradients of age and metallicity over a large mass range , from 10 ^ { 7 } M _ { \odot } to 10 ^ { 12 } M _ { \odot } ( -9.2 > M _ { B } > -22.4 mag ) .
The well-known mass-metallicity relation is continuous throughout the whole mass range , in the sense that more massive galaxies are more metal-rich .
The age-mass relation is consistent with the idea of downsizing : smaller galaxies have more extended star-formation histories than more massive ones .
The transition type dwarfs ( intermediate between dwarf irregular and dwarf elliptical galaxies ) deviate from this relation having younger mean age , and the low-mass dwarf spheroidals have older ages , marking a discontinuity in the relation , possibly due to selection effects .

In all mass regimes , the mean metallicity gradients are approximately -0.2 and the mean age gradients +0.1 dex per decade of radius .
The individual gradients are widely spread : -0.1 < \nabla _ { Age } < 0.4 and -0.54 < \nabla _ { [ { Fe / H } ] } < +0.2 .
We do not find evidence for a correlation between the metallicity gradient and luminosity , velocity dispersion , central age or age gradient .
Likewise , we do not find a correlation between the age gradient and any other parameter in bright early-type galaxies .
In faint early-types with M _ { B } \gtrsim - 17 mag , on the other hand , we find a strong correlation between the age gradient and luminosity : the age gradient becomes more positive for fainter galaxies .
Together with the observed downsizing phenomenon this indicates that , as time passes , star formation persists in dwarf galaxies and becomes more centrally concentrated .
However , this prolonged central star formation is not reflected in the metallicity profiles of the dwarfs in our sample .

We conclude that various physical mechanisms can lead to similar gradients and that these gradients are robust against the environmental effects .
In particular , the gradients observed in dwarfs galaxies certainly survived the transformation of the progenitors through tidal harassment or/and ram-pressure stripping .
The diversity of metallicity gradients amongst dwarf elliptical galaxies may reflect a plurality of progenitors ’ morphologies .
The dwarfs with steep metallicity gradients could have originated from blue compact dwarfs and those with flat profiles from dwarf irregulars and late type spirals .