Structure and evolution of starburst and normal galaxies

A comparative study of the rest-frame morphology and structural properties of optically selected starburst galaxies at redshift zless than or similar to1 is carried out using multi-wave-band (BViz) high-resolution images taken by the Advanced Camera for Surveys as part of the Great Observatories Origins Deep Survey. We classify galaxies into starburst, early, and late types by comparing their observed spectral energy distributions with local templates. We find that early-type systems have significantly higher rest-frame B-band concentration indices and active galacic nucleus (AGN) fraction (>25%) than late-type spirals and optically selected starbursts. These results are consistent with the scenario that early-epoch (z>>1) gas-rich dissipative processes (e.g., major mergers) have played an important role in developing large central concentrations in early-type E/Sa galaxies and that a concurrent growth of central black holes and bulges occurs in some of these early merger events. The lower AGN fraction and concentration indices in the majority of the optically selected starbursts at zless than or similar to1 suggest that either the starbursts and early types are different in nature (being, respectively, disk and bulge dominated) and/or they are in different evolutionary phases, such that some of the starbursts in major mergers evolve into early types as the dynamical phase of the merger evolves and the spectral signature of the starburst fades out. The starbursts have, on average, larger asymmetries than our control sample of normal galaxies in both rest-frame B and R bands, suggesting that a significant fraction of the starburst activity is tidally triggered.