  The photospheric spatial distribution of the main magnetic polarities of
bipolar active regions (ARs) presents during their emergence deformations are
known as magnetic tongues. They are attributed to the presence of twist in the
toroidal magnetic flux-tubes that form the ARs. The aim of this article is to
study the twist of newly emerged ARs from the evolution of magnetic tongues
observed in photospheric line-of-sight magnetograms. We apply the procedure
described by Poisson et al. (2015, Solar Phys. 290, 727) to ARs observed over
the full Solar Cycle 23 and the beginning of Cycle 24. Our results show that
the hemispherical rule obtained using the tongues as a proxy of the twist has a
weak sign-dominance (53 % in the southern hemisphere and 58 % in the northern
hemisphere). By defining the variation of the tongue angle, we characterize the
strength of the magnetic tongues during different phases of the AR emergence.
We find that there is a tendency of the tongues to be stronger during the
beginning of the emergence and to become weaker as the AR reaches its maximum
magnetic flux. We compare this evolution with the emergence of a toroidal
flux-rope model with non-uniform twist. The variety of evolution of the tongues
in the analyzed ARs can only be reproduced when using a broad range of twist
profiles, in particular having a large variety of twist gradient in the
direction vertical to the photosphere. Although the analytical model used is a
special case, selected to minimize the complexity of the problem, the results
obtained set new observational constraints to theoretical models of flux-rope
emergence that form bipolar ARs.
