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Our understanding of how the size of galaxies has evolved over cosmic time isbased on the use of the half-light (effective) radius as a size indicator.Although the half-light radius has many advantages for structurallyparameterising galaxies, it does not provide a measure of the global extent ofthe objects, but only an indication of the size of the region containing theinnermost 50% of the galaxy's light. Therefore, the observed mild evolution ofthe effective radius of disc galaxies with cosmic time is conditioned by theevolution of the central part of the galaxies rather than by the evolutionaryproperties of the whole structure. Expanding on the works by Trujillo et al.(2020) and Chamba et al. (2022), we study the size evolution of disc galaxiesusing as a size indicator the radial location of the gas density threshold forstar formation. As a proxy to evaluate this quantity, we use the radialposition of the truncation (edge) in the stellar surface mass density profilesof galaxies. To conduct this task, we have selected 1048 disc galaxies withM$_{\rm stellar}$ $>$ 10$^{10}$ M$_{\odot}$ and spectroscopic redshifts up toz=1 within the HST CANDELS fields. We have derived their surface brightness,colour and stellar mass density profiles. Using the new size indicator, theobserved scatter of the size-mass relation (~0.1 dex) decreases by a factor of~2 compared to that using the effective radius. At a fixed stellar mass, MilkyWay-like (M$_{\rm stellar}$ ~ 5$\times$10$^{10}$ M$_{\odot}$) disc galaxieshave on average increased their sizes by a factor of two in the last 8 Gyr,while the surface stellar mass density at the edge position has decreased bymore than an order of magnitude from ~13 M$_{\odot}$/pc$^2$ (z=1) to ~1M$_{\odot}$/pc$^2$ (z=0). These results reflect a dramatic evolution of theouter part of MW-like disc galaxies, growing ~1.5 kpc Gyr$^{-1}$.

Strong size evolution of disc galaxies since z = 1: Readdressing galaxy growth using a physically motivated size indicator