Observational Cosmology Seminar

Galaxy cluster mergers are rich sources of information to test cluster astrophysics and cosmology. However, mergers produce complex projected signals that are difficult to interpret from individual observational probes. Multi-probe constraints on both the gas and dark matter cluster components are necessary to infer merger parameters that are otherwise degenerate. We have developed ICM-SHOX (Improved Constraints on Mergers with SZ, Hydrodynamical simulations, Optical, and X-ray), a systematic framework to jointly infer cluster merger parameters quantitatively via a pipeline that directly compares a novel combination of multi-probe observables to mock observables derived from MHD simulations. In our first application of the ICM-SHOX pipeline to the MACS J0018.5+1626 system, we discovered a velocity-space decoupling of the gas and dark matter distributions, which we attribute to the different collisional properties of the two components. In another system, MACS J2129.4-0741, we find hints of a Bullet Cluster-like morphology in the X-ray data, which strongly suggests a plane-of-sky merger, alongside high line of sight velocities in both the gas and dark matter, which simultaneously suggests a merger in that direction. In the first part of this talk, I will provide an overview of these exciting cluster mergers and the status of our updated ICM-SHOX pipeline. In the second part of this talk, I will describe an ongoing effort to explore the possibility that inverse-Compton scattering of CMB photons by ~GeV cosmic rays (CR-IC) injected by the central AGN in cool core clusters produces a non-negligible continuum-like X-ray signal that is easily misinterpreted as ICM thermal bremsstrahlung continuum. In particular, I will highlight our comparison of thermodynamic profiles derived from SZ and X-ray observations of the ZwCl 3146 cluster to assess whether CR-IC could be relevant to the cooling flow problem.