  Our understanding of how the size of galaxies has evolved over cosmic time is
based on the use of the half-light (effective) radius as a size indicator.
Although the half-light radius has many advantages for structurally
parameterising galaxies, it does not provide a measure of the global extent of
the objects, but only an indication of the size of the region containing the
innermost 50% of the galaxy's light. Therefore, the observed mild evolution of
the effective radius of disc galaxies with cosmic time is conditioned by the
evolution of the central part of the galaxies rather than by the evolutionary
properties 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 galaxies
using as a size indicator the radial location of the gas density threshold for
star formation. As a proxy to evaluate this quantity, we use the radial
position of the truncation (edge) in the stellar surface mass density profiles
of galaxies. To conduct this task, we have selected 1048 disc galaxies with
M$_{\rm stellar}$ $>$ 10$^{10}$ M$_{\odot}$ and spectroscopic redshifts up to
z=1 within the HST CANDELS fields. We have derived their surface brightness,
colour and stellar mass density profiles. Using the new size indicator, the
observed 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, Milky
Way-like (M$_{\rm stellar}$ ~ 5$\times$10$^{10}$ M$_{\odot}$) disc galaxies
have 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 by
more than an order of magnitude from ~13 M$_{\odot}$/pc$^2$ (z=1) to ~1
M$_{\odot}$/pc$^2$ (z=0). These results reflect a dramatic evolution of the
outer part of MW-like disc galaxies, growing ~1.5 kpc Gyr$^{-1}$.

Astrophysics of Galaxies