  Thick disk evolution is studied using edge-on galaxies in two Hubble Space
Telescope Frontier Field Parallels. The galaxies were separated into 72 clumpy
types and 35 spiral types with bulges. Perpendicular light profiles in F435W,
F606W and F814W (B, V and I) passbands were measured at 1 pixel intervals along
the major axes and fitted to sech^2 functions convolved with the instrument
line spread function (LSF). The LSF was determined from the average point
spread function (PSF) of ~20 stars in each passband and field, convolved with a
line of uniform brightness to simulate disk blurring. A spread function for a
clumpy disk was also used for comparison. The resulting scale heights were
found to be proportional to galactic mass, with the average height for a
10^9.5-10^10.5 Msun galaxy at z=1.5-2.5 equal to 0.63+-0.24 kpc. This value is
probably the result of a blend between thin and thick disk components that
cannot be resolved. Evidence for such two-component structure is present in an
inverse correlation between height and midplane surface brightness. Models
suggest that the thick disk is observed best between the clumps, and there the
average scale height is 1.06+-0.43 kpc for the same mass and redshift. A
0.63+-0.68 mag V-I color differential with height is also evidence for a
mixture of thin and thick components.
