Title: Close Major-Merger Pairs: Merger Rate, SFR Enhancement, and Cosmic Evolution

Speaker: Prof. C. Kevin Xu
Institute: California Institute of Technology
Time: 2018.06.07(Thursday) 14:30-16:30
Place: Physics Building 552, Haiyun Campus, Xiamen University

Abstract: I will present results on cosmic evolution of galaxy pairs based on studies of two large samples: a local sample (KPAIR, 170 pairs), and amid-z sample (0.2 < z < 1) selected in the COSMOS field (CPAIR,more than 300 pairs). We found that, since z=1, the pair fraction evolves as (1+z)^(2.2+-0.2). Major mergers involving star-forming galaxies (i.e., wet and mixed mergers) have significant impact on the stellar mass assembly of massive galaxies, and are sufficiently abundant to account for the formation of massive ellipticals. Results from our FIR observations using Spitzer and Herschel revealed a puzzling difference between star-forming galaxies in mixed pairs (S+E) and in wet pairs (S+S) in the sense that, relative to single spiral galaxies, spirals paired with ellipticals show no SFR enhancement while spirals paired with spirals show strong enhancement. Furthermore, the SFR enhancement in S+S pairs decreases (with increasing redshift) substantially between z=0 and z=1. I will discuss some plausible interpretations for these results which may provide new clues to the still evasive theory of merger-induced starbursts.