COSMIC RAYS MASQUERADING AS COOL CORES: AN INVERSE-COMPTON ORIGIN FOR COOL CORE CLUSTER EMISSION

X-ray bright cool-core (CC) clusters ubiquitously contain luminous radio sources accelerating cosmic ray (CR) leptons at prodigious rates. Near the acceleration region, high-energy leptons produce synchrotron (mini)halos and sometimes observable-rays, but these leptons have short lifetimes and so cannot propagate far from sources without some rejuvenation. However, low-energy (0.1 − 1 GeV) CRs should survive for Gyr, potentially reaching 100 kpc before losing most of their energy via inverse-Compton (IC) scattering of CMB photons to keV X-ray energies, with remarkably thermal X-ray spectra. In groups/clusters, this will appear similar to relatively “cool” gas in cluster cores, i.e. CCs. In lower-mass (e.g. Milky Way/M31) halos, analogous CR IC emission will appear as hot (super-virial) gas at outer CGM radii, explaining recent diffuse X-ray observations. We show that for plausible (radio/-ray observed) lepton injection rates, the CR-IC emission could contribute significantly to the X-ray surface brightness (SB) in CCs, implying that CC gas densities may have been significantly overestimated and alleviating the cooling flow problem. A significant IC contribution to the diffuse X-ray emission in CC clusters also explains the tight correlation between the X-ray “cooling luminosity” and AGN/cavity/jet power even absent significant feedback heating, because the apparent CC emission is itself driven by the radio source. Comparing observed Sunyaev Zeldovich-to-X-ray inferred pressures at 100 kpc in CCs represents a clean test of this scenario, and existing data appears to favor significant CR-IC. A significant IC contribution also implies that X-ray inferred gas-phase metallicities have been underestimated in CCs, potentially explaining the discrepancy between X-ray (sub-Solar) and optical/UV (super-Solar) observed metallicities in the central 10 kpc of nearby CCs. We also discuss our model’s connection to observations of multiphase gas in clusters.