Issue |
A&A
Volume 488, Number 3, September IV 2008
|
|
---|---|---|
Page(s) | 861 - 865 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:200809920 | |
Published online | 17 July 2008 |
Evolution of low-frequency features in the CMB spectrum due to stimulated Compton scattering and Doppler broadening
1
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching bei München, Germany e-mail: jchluba@mpa-garching.mpg.de
2
Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
Received:
7
April
2008
Accepted:
25
June
2008
We discuss a new analytic solution of the
Kompaneets equation for physical situations in which low frequency photons,
forming relatively narrow spectral details, are Compton scattered in an
isotropic, infinite medium with an intense ambient blackbody field that is
very close to full thermodynamic equilibrium with the free electrons.
In this situation the background-induced stimulated Compton scattering
slows down the motion of photons toward higher frequencies by a factor of
3 in comparison with the solution that only takes Doppler broadening and
boosting into account.
This new solution is important for detailed computations of cosmic microwave
background spectral distortions arising from uncompensated atomic
transitions of hydrogen and helium in the early Universe.
It also clearly shows that the broadening of weak lines in this situation
only depends on the Compton y-parameter defined by Te, even though the
evolution of the ambient CMB blackbody spectrum itself is described by
.
In addition, we derive another analytic solution that only includes the
background-induced stimulated Compton scattering and is valid for power law
ambient radiation fields.
This solution might have interesting applications for radio lines arising
inside of bright extra-galactic radio sources,
where according to our estimates line shifts because of background-induced
stimulated scattering could be amplified and even exceed the line broadening
due to the Doppler effect.
Key words: cosmology: theory / cosmology: cosmic microwave background / line: formation / radiative transfer / scattering
© ESO, 2008
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