Projected axis ratio measurements of 880 early-type galaxies at redshifts 1 < z < 2.5 selected from CANDELS are used to reconstruct and model their intrinsic shapes .
The sample is selected on the basis of multiple rest-frame colors to reflect low star-formation activity .
We demonstrate that these galaxies as an ensemble are dust-poor and transparent and therefore likely have smooth light profiles , similar to visually classified early-type galaxies .
Similar to their present-day counterparts , the z > 1 early-type galaxies show a variety of intrinsic shapes ; even at a fixed mass , the projected axis ratio distributions can not be explained by the random projection of a set of galaxies with very similar intrinsic shapes .
However , a two-population model for the intrinsic shapes , consisting of a triaxial , fairly round population , combined with a flat ( c / a \sim 0.3 ) oblate population , adequately describes the projected axis ratio distributions of both present-day and z > 1 early-type galaxies .
We find that the proportion of oblate versus triaxial galaxies depends both on the galaxies ’ stellar mass , and - at a given mass - on redshift .
For present-day and z < 1 early-type galaxies the oblate fraction strongly depends on galaxy mass .
At z > 1 this trend is much weaker over the mass range explored here ( 10 ^ { 10 } < M _ { * } / M _ { \odot } < 10 ^ { 11 } ) , because the oblate fraction among massive ( M _ { * } \sim 10 ^ { 11 } M _ { \odot } ) was much higher in the past : 0.59 \pm 0.10 at z > 1 , compared to 0.20 \pm 0.02 at z \sim 0.1 .
When combined with previous findings that the number density and sizes of early-type galaxies substantially increase over the same redshift range , this can be explained by the gradual emergence of merger-produced elliptical galaxies , at the expense of the destruction of pre-existing disks that were common among their high-redshift progenitors .
In contrast , the oblate fraction among low-mass early-type galaxies ( \log ( M _ { * } / M _ { \odot } ) < 10.5 ) increased toward the present , from 0.38 \pm 0.11 at z > 1 to 0.72 \pm 0.06 at z = 0 .
We speculate that this lower incidence of disks at early cosmic times can be attributed to two factors : low-mass , star-forming progenitors at z > 1 were not settled into stable disks to the same degree as at later cosmic times , and the stripping of gas from star-forming disk galaxies in dense environments is an increasingly important process at lower redshifts .