We examine in this paper a stellar mass selected sample of galaxies at 1 < z < 3 within the Hubble Ultra Deep Field , utilising WFC3 imaging to study the rest-frame optical morphological distribution of galaxies at this epoch .
We measure how apparent morphologies ( disk , elliptical , peculiar ) correlate with physical properties , such as quantitative structure and spectral-types .
One primary result is that apparent morphology does not correlate strongly with stellar populations , nor with galaxy structure at this epoch , suggesting a chaotic formation history for Hubble types at z > 1 .
By using a locally defined definition of disk and elliptical galaxies based on structure and spectral-type , we find no true ellipticals at z > 2 , and a fraction of 3.2 \pm 2.3 % at 1.5 < z < 2 .
Local counterparts of disk galaxies are at a similar level of 7 - 10 % , much lower than the 75 % fraction at lower redshifts .
We further compare WFC3 images with the rest-frame UV view of galaxies from ACS imaging , showing that galaxies imaged with ACS that appear peculiar often contain an ‘ elliptical ’ like morphology in WFC3 .
We show through several simulations that this larger fraction of elliptical-like galaxies is partially due to the courser PSF of WFC3 , and that the ‘ elliptical ’ class very likely includes early-type disks .
We also measure the merger history for our sample using CAS parameters , finding a redshift evolution increasing with redshift , and a peak merger fraction of \sim 30 % at z \sim 2 for the most massive galaxies with M _ { * } > 10 ^ { 10 } M _ { \odot } , consistent with previous results from ACS and NICMOS .
We also compare our results to semi-analytical model results and find a relatively good agreement between our morphological break-down and the predictions .
We finally argue that galaxies classified visually as peculiar , elliptical and as peculiar ellipticals , all have similar structural and stellar population properties , suggesting that these galaxies are in a similar formation mode , likely driven by major mergers .