Galaxy structure and morphology at high redshift

Abstract

This review gives an introduction to the recent structural and morphological studies of high-z galaxies based on Hubble Space Telescope Wide Field Camera 3 (HST WFC3) near-infrared imaging. Quiescent galaxies at 1 < z < 3 have been found to be more compact than their local counterparts and show a significant structural evolution on redshift. The recent observations show the evidences suggesting that the evolution of high-z compact quiescent galaxies follows an ‘inside-out’ scenario and the dry minor merger may play a major role. At z > 1, the structural evolution of normal star forming galaxies matches the expectation of hierarchical clustering model. Most of high-z starburst galaxies, including ultraluminous infrared galaxies (ULIRGs), dust-obscured galaxies (DOGs) and submillimeter galaxies (SMGs), show significant merging morphological features, suggesting that major mergers are probably the main triggering mechanism of starburst activities. Morphological studies of high-z active galactic nucleus (AGNS) host galaxies reveal a mixed result. X-ray-selected AGNs with moderate luminosities do not show an enhanced merger fraction than normal galaxies. However, luminous quasars seem to have a high merger fraction. Major mergers have been suggested to be responsible only for triggering luminous AGN activities. In final, based on available observational facts so far, an evolutionary sequence of high-z galaxies, involving starburst galaxies, compact star forming galaxies, quasars and compact quiescent galaxies, has been proposed.