An excessively massive thick disc of the enormous edge-on lenticular
  galaxy NGC7572
  Galactic discs are known to have a complex multilayer structure. An in-depth
study of the stellar population properties of the thin and thick components can
elucidate the formation and evolution of disc galaxies. Even though thick discs
are ubiquitous, their origin is still debated. Here we probe the thick disc
formation scenarios by investigating NGC7572, an enormous edge-on galaxy having
$R_{25}\approx 25$ kpc and $V_{\rm rot} \approx 370$ km s$^{-1}$, which
substantially exceeds the Milky Way size and mass. We analysed DECaLS archival
imaging and found that the disc of NGC7572 contains two flaring stellar discs
(a thin and a thick disc) with similar radial scales. We collected deep
long-slit spectroscopic data using the 6m Russian BTA telescope and analysed
them with a novel technique. We first reconstructed a non-parametric stellar
line-of-sight velocity distribution along the radius of the galaxy and then
fitted it with two kinematic components accounting for the orbital distribution
of stars in thin and thick discs. The old thick disc turned out to be 2.7 times
as massive as the intermediate-age thin component, $1.6\times 10^{11}$
$\textrm{M}_{\odot}$ vs. $5.9\times10^{10}$ $\textrm{M}_{\odot}$, which is very
unusual. The different duration of the formation epochs evidenced by the
[Mg/Fe] values of +0.3 and +0.15 dex for the thick and thin discs respectively,
their kinematics and the mass ratio suggest that in NGC7572 we observe a
rapidly formed very massive thick disc and an underdeveloped thin disc, whose
growth ended prematurely due to the exhaustion of the cold gas likely because
of environmental effects.
