Photometric scaling relations of antitruncated stellar discs in S0-Scd
  galaxies
  It has been recently found that the characteristic photometric parameters of
antitruncated discs in S0 galaxies follow tight scaling relations. We
investigate if similar scaling relations are satisfied by galaxies of other
morphological types. We have analysed the trends in several photometric planes
relating the characteristic surface brightness and scalelengths of the breaks
and the inner and outer discs of local antitruncated S0-Scd galaxies, using
published data and fits performed to the surface brightness profiles of two
samples of Type-III galaxies in the R and Spitzer 3.6 microns bands. We have
performed linear fits to the correlations followed by different galaxy types in
each plane, as well as several statistical tests to determine their
significance. We have found that: 1) the antitruncated discs of all galaxy
types from Sa to Scd obey tight scaling relations both in R and 3.6 microns, as
observed in S0s; 2) the majority of these correlations are significant
accounting for the numbers of the available data samples; 3) the trends are
clearly linear when the characteristic scalelengths are plotted on a
logarithmic scale; and 4) the correlations relating the characteristic surface
brightnesses of the inner and outer discs and the breaks with the various
characteristic scalelengths significantly improve when the latter are
normalized to the optical radius of the galaxy. The results suggest that the
scaling relations of Type-III discs are independent of the morphological type
and the presence (or absence) of bars within the observational uncertainties of
the available datasets, although larger and deeper samples are required to
confirm this. The tight structural coupling implied by these scaling relations
impose strong constraints on the mechanisms proposed for explaining the
formation of antitruncated stellar discs in the galaxies across the whole
Hubble Sequence (Abridged).
