Table 4: Linear fits and probability of no correlation between the metallicity gradient and the gradient of velocity dispersion. N: number of galaxies in the fit; $b+\sigma (b)$: slope and error of the linear fit (the errors have been calculated by Monte Carlo simulations, as described in the text); t: t-statistic to verify the hypothesis "b=0'' (a t value higher than 1.96 allows the hypothesis to be rejected, with a significance level lower than 0.05); Pnc: probability of no correlation in a non-parametric Spearman test.
  N $b+\sigma (b)$ t Pnc
grad age 54 $ 1.727\pm 3.099$ 0.56 0.885
grad [M/H] 54 $ 0.175\pm 0.269$ 0.65 0.238
grad [M/H] (CN2-H$\beta $) 54 $ 1.134\pm 0.555$ 2.04 0.002
grad [M/H] (Ca4227-H$\beta $) 54 $ 0.449\pm 0.686$ 0.65 0.063
grad [M/H] (Fe4383-H$\beta $) 54 $ -0.392\pm 0.442$ 0.89 0.900
grad [M/H] (C4668-H$\beta $) 54 $ 0.451\pm 0.356$ 1.27 0.062
grad [M/H] (Mgb-H$\beta $) 54 $ 0.876\pm 0.463$ 2.11 0.001

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