Yun-Hsin Hsu(ASIAA/NTHU); Yen-Ting Lin(ASIAA); Gabriel Torrealba(ASIAA); Dylan Nelson(MPA); Song Huang(Princeton)
Numerical simulations of ΛCDM suggest that central galaxies in massive dark matter halos, also known as the brightest cluster galaxies (BCGs), have undergone many merging events at redshift z < 1. Observationally verifying such a prediction is not only key in validating the ΛCDM structure formation paradigm, but also central to our understanding of the formation of the most massive galaxies in the universe. This work aims to look for BCGs with multiple cores (indicative of a merger in progress), and the ultimate goal is to constrain merger rates associated with these massive galaxies, as a function of cluster mass. Our BCG sample is extracted from the MaNGA survey, which provides spatially resolved velocity information for each of our BCGs, and allows us to robustly distinguish real associations of the cores with the main body of the BCG from chance projections. Taking advantage of MaNGA, we present the measurement of the frequency of BCGs with multiple cores of the largest IFU sample of BCGs. Moreover, this frequency of multiple cores can be combined with the merger timescale to derive the merger rate of BCGs. The merger time scale is derived from the state-of-the-art cosmological hydrodynamical simulations, 300 Mpc box of illustrisTNG simulation. We trace the merging events of BCGs in the simulation, and the time it appears as multiple-core that satisfies our observational criteria. Here we present the techniques we developed and show some preliminary results of the merger rate.