The Rest - Frame Fuv Morphologies of Star - Forming Galaxies at Z ∼ 1 . 5 and Z ∼ 4

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 Fields. We compare the distributions of the Gini coefficient (G), second-order moment of the brightest 20% of galaxy light (M20), and concentration (C) for high-redshift and low-redshift galaxies with average signal to noise 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 MFUV < −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 post-mergers. The star-forming z ∼ 1.5 galaxy sample has a morphological distribution which 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. Subject headings: galaxies:evolution – galaxies:high-redshift – galaxies:interacting – galaxies:structure – ultraviolet:galaxies