Investigating the Effect of Galaxy Interactions on Star Formation at 0.5 < z < 3.0

Observations and simulations of interacting galaxies and mergers in the local universe have shown that interactions can significantly enhance the star formation rates (SFRs) and fueling of active galactic nuclei (AGN). However, at higher redshift, some simulations suggest that the level of star formation enhancement induced by interactions is lower due to the higher gas fractions and already increased SFRs in these galaxies. To test this, we measure the SFR enhancement in a total of 2351 (1327) massive (M * > 1010 M ⊙) major (1 < M 1/M 2 < 4) spectroscopic galaxy pairs at 0.5 < z < 3.0 with ΔV < 5000 km s−1 (1000 km s−1) and projected separation <150 kpc selected from the extensive spectroscopic coverage in the COSMOS and CANDELS fields. We find that the highest level of SFR enhancement is a factor of 1.23−0.09+0.08 in the closest projected separation bin (<25 kpc) relative to a stellar mass-, redshift-, and environment-matched control sample of isolated galaxies. We find that the level of SFR enhancement is a factor of ∼1.5 higher at 0.5 < z < 1 than at 1 < z < 3 in the closest projected separation bin. Among a sample of visually identified mergers, we find an enhancement of a factor of 1.86−0.18+0.29 (∼3σ) for coalesced systems. For this visually identified sample, we see a clear trend of increased SFR enhancement with decreasing projected separation (2.40 −0.37+0.62 versus 1.58−0.20+0.29 for 0.5 < z < 1.6 and 1.6 < z < 3.0, respectively). The SFR enhancements seen in our interactions and mergers are all lower than the level seen in local samples at the same separation, suggesting that the level of interaction-induced star formation evolves significantly over this time period.