Speaker
Christoph Pfrommer
Description
It has been realised only recently that TeV emission from
blazars can significantly heat the intergalactic medium by
pair-producing high-energy electrons and positrons, which in
turn excite vigorous plasma instabilities, leading to a
local dissipation of the pairs’ kinetic energy. This heats
the intergalactic medium and dramatically increases its
entropy after redshift z~2, with important implications for
the formation of galaxy clusters and dwarf galaxies. This
suggests a scenario for the origin of the cool core
(CC)/non-cool core (NCC) bimodality in galaxy clusters and
groups. Early forming galaxy groups are unaffected because
they can efficiently radiate the additional entropy,
developing a CC. However, late forming groups do not have
sufficient time to cool before the entropy is
gravitationally reprocessed through successive mergers -
counteracting cooling and raising the core entropy further.
Hence blazar heating works different than feedback by active
galactic nuclei (AGN), which balances radiative cooling but
is unable to transform CC into NCC clusters due to the weak
coupling to the cluster gas. Similar to AGN feedback, blazar
heating suppresses the Sunyaev-Zel'dovich power spectrum on
angular scales smaller than 5' due to the globally reduced
central pressure of groups and clusters forming after z~1.
This allows for a larger rms amplitude of the density power
spectrum, sigma_8, and may reconcile SZ-inferred values with
those by other cosmological probes even after allowing for a
contribution due to patchy reionization.
