Stellar mass distribution of S$^4$G disk galaxies and signatures of bar-induced secular evolution

We use 3.6 $\mu$m photometry from the Spitzer Survey of Stellar Structure in Galaxies (S$^{4}$G) to trace the stellar distribution in nearby disk galaxies ($z\approx0$) with total stellar masses $10^{8.5}\lesssim M_{\ast}/M_{\odot}\lesssim10^{11}$ and mid-IR Hubble types $-3 \le T \le 10$, and to provide observational constraints for galaxy formation models to be checked against. For 1154 galaxies with disk inclinations lower than $65^{\circ}$, we Fourier decompose and rescale their images to a common frame determined (i) by the size in physical units, (ii) by their disk scalelength, and for 748 barred galaxies (iii) by both the length and orientation of their bars. We stack the resized density profiles and images to obtain statistically representative average stellar disks and bars in bins of $M_{\ast}$ and $T$. We also calculate the mean stellar contribution to the circular velocity. We infer the gravitational potentials from the synthetic bars to obtain the tangential-to-radial force ratio ($Q_{\rm T}$) and $A_2$ profiles in the different bins. We provide observational evidence for bar-induced secular evolution of disk galaxies. For $M_{\ast} \ge 10^{9}M_{\odot}$, we find a significant difference in the stellar density profiles of barred and non-barred systems: (i) disks in barred galaxies show larger scalelengths ($h_{\rm R}$) and fainter extrapolated central surface brightnesses ($\Sigma_{0}$), (ii) the mean surface brightness profiles ($\Sigma_{\ast}$) of barred and non-barred galaxies intersect each other slightly beyond the mean bar length, most likely at the bar corotation, and (iii) the central mass concentration of barred galaxies is larger (by almost a factor 2 when $T\le5$) than in their non-barred counterparts. We also show that bars hosted by early-type galaxies are more centrally concentrated and have larger density amplitudes than their late-type counterparts (Abridged).