Date:
Tue, 26/05/200912:15-13:15
Location:
Kaplun Bldg, seminar room, 2nd floor
Relativistic particle population and magnetic fields in clusters of
galaxies
We show that the observed correlation between the radio luminosity and the thermal X-ray luminosity in radio emitting galaxy clusters implies that the radio emission is due to secondary electrons, that are produced by p-p interactions and lose their energy by emitting synchrotron radiation in a strong magnetic field, B>(8\pi a T_{CMB}^4)^{1/2}\simeq 3 muG. We construct a simple model that naturally explains the correlation, and show that the observations provide stringent constraints on cluster magnetic fields and cosmic rays (CRs): Within the cores of clusters, the ratio between the CR energy (per logarithmic particle energy interval) and the thermal energy is \beta_{core}\sim 2*10^{-4}; The source of these CRs is most likely the cluster accretion shock, which is inferred to deposit in CRs ~0.1 of the thermal energy it generates; The diffusion time of 100 GeV CRs over scales \gtrsim 100 kpc is not short compared to the Hubble time; Cluster magnetic fields are enhanced by mergers to \gtrsim 1percent of equipartition, and decay (to < 1 \muG) on 1 Gyr time scale.
We show that the hard X-ray (HXR) emission of galaxy clusters is most likely produced by inverse Compton scattering of CMB photons by electrons accelerated in accretion shocks. We find that the accretion shock luminosity exceeds the luminosity produced by secondary particles by a factor of \simeq 10^3(\eta_e/\eta_p)(T/10 keV)^{-1/2}, where T is the cluster temperature and \eta_{p(e)} is the fraction of the thermal energy generated in strong collisionless shocks, which is deposited in CR protons (electrons). Simple estimates of the mass accretion rate of galaxy clusters allow us to infer \eta_{e}\sim few percents.
The implications of our predictions to future HXR (e.g. NuStar, Simbol-X) and (space and ground based) gamma-ray observations (e.g. Fermi, HESS, MAGIC, VERITAS) are discussed. We predict that the gamma-ray emission from clusters of galaxies should be extended, and the inferred value of \eta_{e} implies that this extended emission should be easily detectable. On the other hand, the inferred value of \beta_{core} implies that high energy gamma-ray emission from secondaries at cluster cores will be difficult to detect with existing and planned instruments.
galaxies
We show that the observed correlation between the radio luminosity and the thermal X-ray luminosity in radio emitting galaxy clusters implies that the radio emission is due to secondary electrons, that are produced by p-p interactions and lose their energy by emitting synchrotron radiation in a strong magnetic field, B>(8\pi a T_{CMB}^4)^{1/2}\simeq 3 muG. We construct a simple model that naturally explains the correlation, and show that the observations provide stringent constraints on cluster magnetic fields and cosmic rays (CRs): Within the cores of clusters, the ratio between the CR energy (per logarithmic particle energy interval) and the thermal energy is \beta_{core}\sim 2*10^{-4}; The source of these CRs is most likely the cluster accretion shock, which is inferred to deposit in CRs ~0.1 of the thermal energy it generates; The diffusion time of 100 GeV CRs over scales \gtrsim 100 kpc is not short compared to the Hubble time; Cluster magnetic fields are enhanced by mergers to \gtrsim 1percent of equipartition, and decay (to < 1 \muG) on 1 Gyr time scale.
We show that the hard X-ray (HXR) emission of galaxy clusters is most likely produced by inverse Compton scattering of CMB photons by electrons accelerated in accretion shocks. We find that the accretion shock luminosity exceeds the luminosity produced by secondary particles by a factor of \simeq 10^3(\eta_e/\eta_p)(T/10 keV)^{-1/2}, where T is the cluster temperature and \eta_{p(e)} is the fraction of the thermal energy generated in strong collisionless shocks, which is deposited in CR protons (electrons). Simple estimates of the mass accretion rate of galaxy clusters allow us to infer \eta_{e}\sim few percents.
The implications of our predictions to future HXR (e.g. NuStar, Simbol-X) and (space and ground based) gamma-ray observations (e.g. Fermi, HESS, MAGIC, VERITAS) are discussed. We predict that the gamma-ray emission from clusters of galaxies should be extended, and the inferred value of \eta_{e} implies that this extended emission should be easily detectable. On the other hand, the inferred value of \beta_{core} implies that high energy gamma-ray emission from secondaries at cluster cores will be difficult to detect with existing and planned instruments.