tokens: acted at different temporal and spatial scales throughout the lifetime of the galaxies. The size of our sample does not allow for a separate analysis of whether AGNs or bars can play a role in the observed stellar metallicity. However, we observe that the mere presence of an AGN at z = 0 does not necessarily imply that it has played a role in shaping the observed galaxy stellar metallicity. An AGN can be a transient phenomenon in a galaxy. With AGN duty cycles spanning timescales in the range 10 6 − 10 8 yr ( Haehnelt Rees 1993 ; Davis et al. 2014 ; Storchi-Bergmann Schnorr-Müller 2019 ), we expect that the AGN effects on stellar metallicity should be due to past and not current AGN activity. Regarding bars, there is no consensus in the literature as to the longevity of bars, nor how many bar events the average galaxy experiences during its lifetime ( Sellwood 1999 ; Athanassoula 2002 ; Bournaud Combes 2002 ; Elmegreen et al. 2004 ; Combes 2004 ; Regan Teuben 2004 ; Pérez et al. 2008 ; James Percival 2016 ). While several authors have observed a correlation between gas abundance gradients and the presence of bars, in particular, a flattening of the gradient ( Vila-Costas Edmunds 1992 ; Martin Roy 1994 ; Zaritsky et al. 1994 ), more recent works have found no evidence of such a correlation by analysing both gas-phase metallicity and stellar metallicity ( Sánchez et al. 2012b , 2014 ; Sánchez-Blázquez et al. 2014 ; Cheung et al. 2015 ; Sánchez-Menguiano et al. 2016 ). The upper panels of Fig. 2 show the light-weighted metallicity as a function of stellar mass surface density log(Σ ⋆ ) for galaxies in the field and in groups. Field galaxies shown in Fig. 2 are a random realisation of 107 galaxies from the field sample, which were selected to have the same overall mass distribution as the group sample. Each galaxy, in either of the two samples, contributes several points to this figure. The number of points varies from galaxy to galaxy, as does the number of radial bins that each profile has. Points are colour-coded in tones of grey according to their radial distance in terms of the effective radius, r / r e . The solid curves show the number-density iso-contour levels. The stellar mass surface density and metallicity are strongly correlated although we observe significant scatter. To compare galaxies in the field and groups, the upper right panel of Fig. 2 shows the iso-contour for each environment considered. We clearly observe that galaxies in groups are more metallic for a fixed value of stellar mass surface density. Fig. 2. Top panels : light-weighted metallicity as a function of stellar mass surface density Σ ⋆ . Dots are colour-coded in tones of grey according to their distance r / r e . The left panel corresponds to galaxies in the field, the central panel shows galaxies in groups, and the right panel shows the iso-contour levels for galaxies in groups (red lines) and galaxies in the field (blue lines). The bottom panels show the median
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