Disk dominated galaxies retain their shapes below $z = 1.0$
  The high abundance of disk galaxies without a large central bulge challenges
predictions of current hydrodynamic simulations of galaxy formation. We aim to
shed light on the formation of these objects by studying the redshift and mass
dependence of their 3D shape distribution in the COSMOS galaxy survey. This
distribution is inferred from the observed distribution of 2D shapes, using a
reconstruction method which we test using hydrodynamic simulations. We find a
moderate bias for the inferred average disk circularity and relative thickness
with respect to the disk radius, but a large bias on the dispersion of these
quantities. Applying the 3D shape reconstruction method on COSMOS data, we find
no significant dependence of the inferred 3D shape distribution on redshift.
The relative disk thickness shows a significant mass dependence which can be
accounted for by the scaling of disk radius with galaxy mass. We conclude that
the shapes of disk dominated galaxies are overall not subject to disruptive
merging or feedback events below redshift $z=1.0$. This favours a scenario
where these disks form early and subsequently undergo a tranquil evolution in
isolation. In addition, our study shows that the observed 2D shapes of disk
dominated galaxies can be well fitted using an ellipsoidal model for the galaxy
3D morphology combined with a Gaussian model for the 3D axes ratio
distribution, confirming findings from similar work reported in the literature.
Such an approach allows to build realistic mock catalogs with intrinsic galaxy
shapes that will be essential for the study of intrinsic galaxy alignment as a
contaminant of weak lensing surveys.
