Hot gas in superclusters and microwave background distortions

Abstract

Variations in the electron pressure can produce significant distortions of the cosmic microwave background radiation (CMBR) spectrum through the Sunyaev-Zel'dovich effect. In this paper, we compute the amplitude of these distortions in various cosmological scenarios using the results of hydrodynamical simulations combined with analytic theory. For reionized cold dark matter (CDM) with h = 0.5 probed with the OVRO experiment (Theta approximately = 0.1 deg), we find that the amplitude of these fluctuations is (Delta T/T)<SUB>rms</SUB> = 1 x 10<SUP>-5</SUP> (Omega<SUB>i</SUB>/0.06) if the experiment looks at a random part of the sky and 6 x 10<SUP>-6</SUP>(Omega<SUB>i</SUB>/(0.06) if bright areas are avoided. Here Omega is the density of ionized baryons in units of the critical density, rho<SUB>c</SUB> = 2.78 x 10<SUP>11</SUP>h<SUP>2</SUP>/cu Mpc. Primary fluctuations would generate (Delta T/T)<SUB>rms</SUB> approximately = 2 x 10<SUP>-6</SUP> for this model. These distortions could be a dominant source of CMBR anisotropics on small and intermediate angular scales. It is important to note that these signals are generated relatively recently, when nonlinear effects are improtant, and do not require early reionization. We also examine the contribution to anisotropies from the Doppler effect, in both the linear and nonlinear regimes. In this case, the bulk of the signal is generated before a redshift of 10, provided that the intercluster medium is ionized back to the surface of last scattering. On the smallest scales thermal effects are bigger, while, on larger scales the Doppler-induced fluctuations are greater with the exact boundary determined by the scenario. However, over a wide range of scales, the two signals are equal to within a factor of a few.