Polarization of the SunyaevZel'dovich effect: relativistic imprint of thermal and nonthermal plasma
Abstract
Inverse Compton (IC) scattering of the anisotropic CMB fluctuations off cosmic electron plasmas generates a polarization of the associated SunyaevZel'dovich (SZ) effect. The polarized SZ effect has important applications in cosmology and in astrophysics of galaxy clusters. However, this signal has been studied so far mostly in the nonrelativistic regime which is valid only in the very low electron temperature limit for a thermal electron population and, as such, has limited astrophysical applications. Partial attempts to extend this calculation to the IC scattering of a thermal electron plasma in the relativistic regime have been done but these cannot be applied to a more general or mildly relativistic electron distribution. In this paper we derive a general form of the SZ effect polarization that is valid in the full relativistic approach for both thermal and nonthermal electron plasmas, as well as for a generic combination of various electron population which can be cospatially distributed in the environments of galaxy clusters or radiogalaxy lobes. We derive the spectral shape of the Stokes parameters induced by the IC scattering of every CMB multipole for both thermal and nonthermal electron populations, focussing in particular on the CMB quadrupole and octupole that provide the largest detectable signals in cosmic structures (like galaxy clusters). We found that the CMB quadrupole induced Stoke parameter Q is always positive with a maximum amplitude at a frequency ≈ 216 GHz which increases nonlinearly with increasing cluster temperature. On the contrary, the CMB octupole induced Q spectrum shows a crossover frequency which depends on the cluster electron temperature in a linear way, while it shows a nonlinear dependence on the minimum momentum p_{1} of a nonthermal powerlaw spectrum as well as a linear dependence on the powerlaw spectral index of the nonthermal electron population. We discuss some of the possibilities to disentangle the quadrupoleinduced Q spectrum from the octupoleinduced one which will allow to measure these important cosmological quantities through the SZ effect polarization at different cluster locations in the universe. We finally apply our model to the Bullet cluster and derive the visibility windows of the total, quandrupoleinduced and octupoleinduced Stoke parameter Q in the frequency ranges accessible to SKA, ALMA, MILLIMETRON and CORE++ experiments.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 July 2016
 DOI:
 10.1088/14757516/2016/07/031
 arXiv:
 arXiv:1605.08333
 Bibcode:
 2016JCAP...07..031S
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 31 pages, 11 figures, submitted to JCAP