We present radial stellar population parameters for a subsample of 12 galaxies from the 36 isolated early-type galaxies of Reda et al .
Using new long-slit spectra , central values and radial gradients for the stellar age , metallicity [ Z/H ] and \alpha -element abundance [ E/Fe ] are measured .
Similarly , the central stellar population parameters are derived for a further 5 isolated early-type galaxies using their Lick indices from the literature .
On average , the seventeen isolated galaxies have mean central [ Z/H ] _ { o } and [ E/Fe ] _ { o } of 0.29 \pm 0.03 and 0.17 \pm 0.03 respectively and span a wide range of ages from 1.7 to 15 Gyrs .
We find that isolated galaxies follow similar scaling relations between central stellar population parameters and galaxy velocity dispersion to their counterparts in high density environments .
However , we note a tendency for isolated galaxies to have slightly younger ages , higher metallicities and lower abundance ratios .
Such properties are qualitatively consistent with the expectation of an extended star formation history for galaxies in lower density environments .
Generally we measure constant age and [ E/Fe ] radial gradients .
However , three galaxies show remarkable positive age gradients and two galaxies have negative age gradients .
We find that the age gradients anti-correlate with the central galaxy age .
Thus as a young starburst evolves , the age gradient flattens from positive to almost zero .
Metallicity gradients range from near zero to strongly negative .
For our high mass galaxies ( \sigma > 160 km/s ) metallicity gradients are shallower with increasing mass .
Such behaviour is not predicted in dissipational collapse models but might be expected in multiple mergers .
The metallicity gradients are also found to be correlated with the central age and metallicity , as well as to the age gradients .
In conclusion , our stellar population data for a sample of isolated early-type galaxies are more compatible with an extended merger/accretion history than early dissipative collapse .