Refined approximations for the distortion visibility function and mu-type spectral distortions

Abstract

The physical processes affecting the thermalization of cosmic microwave background spectral distortions are very simple and well understood. This allows us to make precise predictions for the distortions signals caused by various energy release scenarios, where the theoretical uncertainty is largely dominated by the physical ingredients that are used for the calculation. Here, we revisit various approximations for the distortion visibility function -- defined using the fraction of the released energy that does not thermalize -- and early $\mu$-type distortions. Our approach is based on a perturbative expansion, which allows us to identify and clarify the origin of different improvements over earlier approximations. It provides a better than ~0.1%-1% description of our numerical results over a wide range of parameters. In particular, we are able to capture the high-frequency part of the mu-distortion, which directly depends on the time derivative of the electron temperature. We also include lowest order double Compton and Compton scattering relativistic corrections, finding that because of cancelation they increase the thermalization efficiency in the tail of the distortion visibility function by only ~10% (at $z\lesssim 6\times 10^6$), although individually their effect can reach ~20%-40%.

19 pages, 14 figures, accepted version MNRAS

References in corpus (6)

• PRISM (Polarized Radiation Imaging and Spectroscopy Mission): An Extended White Paper
• Beyond y and μ: the shape of the CMB spectral distortions in the intermediate epoch, 1.5x10^4 < z < 2x10^5
• Creation of the CMB spectrum: precise analytic solutions for the blackbody photosphere
• ARCADE: Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission
• The double Compton emissivity in a mildly relativistic thermal plasma within the soft photon limit
• Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler-broadening

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