|Time:||Thursday, September 14, 2017, 02:00pm|
|Title:||Mergers of galaxy clusters and their cosmological implications|
|Speaker:||Prof. Qingjuan Yu (PKU)|
Galaxy clusters are the largest virialized systems known in the universe. Mergers of galaxy clusters provide unique laboratories to explore the structure formation in the universe and the nature of dark matter. I’ll talk about our recent study on mergers of galaxy clusters through hydrodynamical simulations and the corresponding cosmological implications of our results. I’ll illustrate the physics to cause the observed offset between the X-ray peak and the Sunyaev–Zel’dovich effect peak of some galaxy clusters and how to use the statistical distribution of the offsets to probe the cosmic velocity field and the cluster merger rate. I’ll talk about the formation of “El Gordo” (probably the most massive galaxy cluster discovered so far at high redshift) by a merger of two progenitor clusters and discuss the challenge to the Lambda CDM cosmological model raised by the very high velocity required in the merger. I’ll present our predictions on some possible observational features of the high-velocity gas motion in the cluster to be tested in the future. I’ll also talk about the important role of baryons in accelerating cluster merging processes and a “no-gas” bias existing in the results obtained from dark matter-only cosmological simulations.