Environmental effects on the star formation activity in galaxies at z ≃ 1.2 in the cosmos field

We investigate the relation between the star formation activity in galaxies and environment at z ≃ 1.2 in the Cosmic Evolution Survey field, using the fraction of [O II] emitters and the local galaxy density. The fraction of [O II] emitters appears to be almost constant over the surface density of galaxies between 0.2 and 10 Mpc^-2. This trend is different from that seen in the local universe where the star formation activity is weaker in higher density regions. To understand this difference between z ∼ 1 and z ∼ 0, we study the fraction of non-isolated galaxies as a function of local galaxy density. We find that the fraction of non-isolated galaxies increases with increasing density. Our results suggest that the star formation in galaxies at z ∼ 1 is triggered by galaxy interaction and/or mergers.