  We have used the HST/ACS images to identify 4700 Lyman break galaxies (LBGs)
in GOODS. We present the results from a parametric analysis of the 2-D surface
brightness profiles, for 1333 LBGs at z > 2.5 with rest-frame UV(1600 Angstrom)
AB magnitude < -20.5. Based on the Sersic index, n, which measures the profile
shape, we find that about 40% of LBGs at z=3 have light profiles close to
exponential, and only 30% have the high concentrations seen for spheroids.
About 30% of LBGs appear to have multiple cores or disturbed morphologies
suggestive of close pairs or on-going mergers. The fraction of spheroid-like (n
> 2.5) LBGs decreases by about 15% from z = 5 to 3. A comparison of LBGs with
the starburst galaxies at z = 1.2, shows that the fraction of spheroid-like
profiles is about 20% higher among LBGs. The ellipticity distribution for LBGs
exhibits a pronounced skew towards high ellipticities (> 0.5), which cannot be
explained by morphologies similar to the local disks and spheroids viewed at
random orientations. The peak of the distribution evolves toward lower
ellipticities, from 0.7 at z = 4 to 0.5 at z = 3. At z = 1.2 the distribution
is relatively flat as seen among the present-day galaxies. The dominance of
elongated morphologies among LBGs suggests that in a significant fraction of
them we may be witnessing star-formation in clumps along gas-rich filaments, or
the earliest gas-rich bars that encompass essentially the entire visible
galaxy. Similar features are found to be ubiquitous in hydrodynamical
simulations in which galaxy formation at high redshifts occurs in filamentary
inflows of dynamically cold gas within the dark matter halos, and involves gas-
rich mergers.
