The Morphological Diversities among Star‐forming Galaxies at High Redshifts in the Great Observatories Origins Deep Survey

Abstract

We used the deep, multiwavelength images obtained by the Great Observatories Origins Deep Survey (GOODS) to identify ~4700 Lyman break galaxies (LBGs) at z > 2.5, and 292 starburst galaxies at z ~ 1.2. We present the results from morphological analysis based on light profile shape and ellipticity for ~1333 of the most luminous LBGs. About 40% of LBGs at z ~ 3 have exponential profiles, ~30% of the galaxies have steep ( r 1/4 -like) profiles, and ~30% of LBGs have multiple cores of disturbed morphologies suggestive of close pairs or mergers. The fraction of spheriod-like LBGs decrease by about 15% from z ~ 5 to 3. A comparison of LBGs with the starburst galaxies at z ~ 1.2 shows that disklike and merger morphologies are dominant, but the fraction of spheroid-like profiles is about 20% higher among LBGs. The ellipticity distribution for LBGs exhibits a pronounced skew toward high ellipticities (ϵ > 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 ϵ, from 0.7 at z = 4 to ~0.5 at z = 3. The ellipticity distribution for the z ~ 1.2 galaxies is relatively flat, similar to that seen for present-day galaxies. The dominance of elongated morphologies suggests that in a significant fraction of LBGs 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.