Issue |
A&A
Volume 424, Number 2, September III 2004
|
|
---|---|---|
Page(s) | 389 - 408 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20041016 | |
Published online | 23 August 2004 |
Superposition of blackbodies and the dipole anisotropy: A possibility to calibrate CMB experiments
1
Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 86740 Garching bei München, Germany e-mail: jchluba@mpa-garching.mpg.de
2
Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32 Moscow, Russia
Received:
3
April
2004
Accepted:
11
May
2004
The CMB angular temperature fluctuations observed by Cobe and
Wmap enable us to place a lower limit on the spectral distortions of the CMB
at any angular scale. These distortions are connected with the simple fact
that the superposition of blackbodies with different temperatures in general
is not a blackbody. We show that in the limit of small temperature
fluctuations the superposition of blackbodies leads to a y-type spectral
distortion.
It is known that the CMB dipole induces a y-type spectral distortion
with quadrupole and monopole angular distribution leading to a
corresponding whole sky y-parameter of .
We show here that taking the difference of the CMB signal in the
direction of the maximum and minimum of the CMB dipole due to the
superposition of two blackbodies
leads to a spectral distortion with
. The amplitude of this distortion can be calculated to the
same precision as the CMB dipole, i.e.
today. Therefore it may
be used as a source with brightness of several or tens of μK to
cross calibrate and calibrate different frequency channels
of CMB surveys with a precision of a few tens or hundreds of nK.
We also discuss clusters of galaxies as possible sources for calibration purposes.
Furthermore, we show in this work that primordial anisotropies for
multipoles
also lead to spectral distortions but
with a much smaller y-parameter, i.e.
.
Key words: cosmology: cosmic microwave background / cosmology: observations
© ESO, 2004
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