Evidence for Morphology and Luminosity Transformation of Galaxies at High Redshifts

We study the galaxy morphology-luminosity-environmental relation and its redshift evolution using a spectroscopic sample of galaxies in the Great Observatories Origins Deep Survey (GOODS). In the redshift range of 0.4 ≤ z ≤ 1.0 we detect conformity in morphology between neighboring galaxies. The realm of conformity is confined within the virialized region associated with each galaxy plus dark matter halo system. When a galaxy is located within the virial radius of its nearest neighbor galaxy, its morphology strongly depends on the neighbor’s distance and morphology: the probability for a galaxy to be an early type (fE) strongly increases as it approaches an early-type neighbor, but tends to decrease as it approaches a late-type neighbor. We find that fE evolves much faster in high density regions than in low density regions, and that the morphology-density relation becomes significantly weaker at z ≈ 1. This may be because the rate of galaxy-galaxy interactions is higher in high density regions, and a series of interactions and mergers over the course of galaxy life eventually transform late types into early types. We find more isolated galaxies are more luminous, which supports luminosity transformation through mergers at these redshifts. Our results are consistent with those from nearby galaxies, and demonstrate that galaxy-galaxy interactions have been strongly affecting the galaxy evolution over a long period of time. Subject headings: galaxies: evolution – galaxies: formation – galaxies: general – galaxies: high-redshift