Shaping the X-ray spectrum of galaxy clusters with AGN feedback and turbulence

Abstract

The hot plasma filling galaxy clusters emits copious X-ray radiation. The classic unheated and unperturbed cooling flow model predicts dramatic cooling rates and an isobaric X-ray spectrum with constant differential luminosity distribution. The observed cores of clusters (and groups) show instead a strong deficit of soft X-ray emission: dLx/dTα(T/Thot)α = 2 ± 1. Using 3D hydrodynamic simulations, we show that such deficit arises from the tight selfregulation between thermal instability condensation and AGN outflow injection: condensing clouds boost the AGN outflows, which quench cooling as they thermalize through the core. The resultant average distribution slope is αa ≃ 2, oscillating within the observed 1< α <3. In the absence of thermal instability, the X-ray spectrum remains isothermal (α ≳ 8), while unopposed cooling drives a too shallowslope, α < 1. AGNoutflows deposit their energy insideout, releasing more heat in the inner cooler phase; radially distributed heating alone induces a declining spectrum, 1