We present an analysis of the structures , sizes , star formation rates , and local environmental properties of galaxies at z \sim 4 - 6 ( \tau _ { universe } < 2 Gyr ) , utilising deep Hubble Space Telescope imaging of the Hubble Ultra Deep Field .
The galaxies we study are selected with the Lyman-break drop-out technique , using galaxies which are B- , V- , and i - drops , which effectively selects UV bright starbursting galaxies between z = 4 and z = 6 .
Our primary observational finding is that starbursting galaxies at z > 4 have a diversity in structure , with roughly 30 % appearing distorted and asymmetric , while the majority are smooth and apparently undisturbed systems .
We utilize several methods to compute the inferred assembly rates for these distorted early galaxies including utilising the CAS system and pair counts .
Overall , we find a similar fraction of galaxies which are in pairs as the fraction which have a distorted structure .
Using the CAS methodology , and our best-estimate for merger time-scales , we find that the total number of inferred effective mergers for M _ { * } > 10 ^ { 9 - 10 } M _ { \odot } galaxies at z < 6 is N _ { m } = 4.2 ^ { +4.1 } _ { -1.4 } .
The more common symmetrical systems display a remarkable scaling relation between the concentration of light and their half-light radii , revealing the earliest known galaxy scaling relationship , and demonstrating that some galaxies at z > 4 are likely in a relaxed state .
Systems which are asymmetric do not display a correlation between size and half-light radii , and are generally larger than the symmetric smooth systems .
The time-scale for the formation of these smooth systems is 0.5-1 Gyr , suggesting that most of these galaxies are formed through coordinated very rapid gas collapses and star formation over a size of 1-2 kpc , or from merger events at z > 10 .
We finally investigate the relation between the UV measured star formation rates for these galaxies and their structures , finding a slight correlation such that more asymmetric systems have slightly higher star formation rates than symmetric galaxies .