The Role of Galaxy Interaction in Environmental Dependence of Star Formation Activity at z ∼ 1.2

Abstract

In order to understand environmental effects on star formation in high-redshift galaxies, we investigate the physical relationships between the star formation activitiy, stellar mass, and environment for z ≃ 1.2 galaxies in the 2 deg^2 COSMOS field. We estimate star formation using the [O II]λ 3727 emission line and environment from the local galaxy density. Our analysis shows that for massive (M* ≥ 10^(10) M☉), the fraction of [O II] emitters in high-density environments is roughly two times higher than in low-density environments, while the [O II] emitter fraction does not depend on environment for low-mass M* ≤ 10^(10) M☉ galaxies. In order to understand what drives these trends, we investigate the role of companion galaxies in our sample. We find massive [O II] emitters are more likely to have companions in high-density environments. These results suggest that interactions and/or mergers in high-density environment could induce star formation in massive galaxies at z ≃ 1.2, increasing the fraction of star-forming galaxies with M* ≥ 10^(10) M☉.

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