Evidence of bar-induced secular evolution in the inner regions of stellar discs in galaxies: what shapes disc galaxies?

We present evidence of bar-induced secular evolution in galactic discs using 3.6 μm images of nearby galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S⁴G). We find that among massive galaxies (M_*/M_⊙ > 10¹⁰), longer bars tend to reside in inner discs having a flatter radial profile. Such galaxies show a light deficit in the disc surrounding the bar, within the bar radius and often show a Θ-shaped morphology. We quantify this deficit and find that among all galaxies explored in this study (with 10⁹ < M_*/M_⊙ < 10¹¹), galaxies with a stronger bar (I.e. longer and/or with a higher Bar/T) show a more pronounced deficit. We also examine simulation snapshots to confirm and extend results by Athanassoula and Misiriotis, showing that as bars evolve they become longer, while the light deficit in the disc becomes more pronounced. Theoretical studies have predicted that, as a barred galaxy evolves, the bar captures disc stars in its immediate neighbourhood so as to make the bar longer, stronger and thinner. Hence, we claim that the light deficit in the inner disc is produced by bars, which thus take part in shaping the mass distribution of their host galaxies.