2006ApJ...636..592L

We apply a new approach to quantifying galaxy morphology and identifying galaxy mergers to the rest-frame far-ultraviolet images of 82 z∼4 Lyman break galaxies (LBGs) and 55 1.2<z<1.8 emission-line galaxies in the GOODS and Ultra Deep Field survey. We compare the distributions of the Gini coefficient (G), the second-order moment of the brightest 20% of galaxy light (M₂₀), and concentration (C) for high- and low-redshift galaxies with average signal-to-noise ratios per pixel >2.5 and Petrosian radii >0".3. Ten of the 82 LBGs have M₂₀≥-1.1 and possess bright double or multiple nuclei, implying a major-merger fraction of star-forming galaxies ∼10%-25% at M_FUV←20, depending on our incompleteness corrections. Galaxies with bulge-like morphologies (G≥0.55, M₂₀←1.6) make up ∼30% of the z∼4 LBG sample, while the remaining ∼50% have G- and M₂₀-values higher than expected for smooth bulges and disks and may be star-forming disks, minor mergers, or postmergers. The star-forming z∼1.5 galaxy sample has a morphological distribution that is similar to the UDF z∼4 LBGs, with an identical fraction of major-merger candidates but fewer spheroids. The observed morphological distributions are roughly consistent with current hierarchical model predictions for the major-merger rates and minor-merger-induced starbursts at z∼1.5 and ∼4. We also examine the rest-frame FUV-NUV and FUV-B colors as a function of morphology and find no strong correlations at either epoch.