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HEALPix and CMBFAST
A widely used solver of the Boltzmann equations for the computation
of theoretical predictions of the spectrum of CMB anisotropy is CMBFAST
(http://www.physics.nyu.edu/matiasz/CMBFAST/cmbfast.html).
CMBFAST makes its outputs in ASCII files, which instead
of CX,l contain quantities defined as
| DX,l |
 |
 |
(4) |
where
TCMB=2.726K is the temperature of the CMB today and X stands for T,
E, B or C (see § A.3).
The version 4.0 of CMBFAST also created a FITS file containing the power spectra
CX,l, designed for interface with HEALPix . The spectra for polarization were renormalized to match the
normalization used in HEALPix 1.1, which was different from the one used by
CMBFAST and by HEALPix 1.2 (see § A.3.2 for details).
The newer version of CMBFAST (4.2, released in Feb. 2003) will generate FITS files containing
CX,l, with the same convention for polarization as the one used
internally. It will therefore match the convention adopted by HEALPix in its
version 1.2.
For backward compatibility, we provide an IDL code (convert_oldhpx2cmbfast)
to change the normalization of existing FITS files created with CMBFAST 4.0.
When created with the correct normalization (with CMBFAST 4.2)
or set to the correct normalization (using convert_oldhpx2cmbfast), the FITS file will include a
specific keyword (POLNORM = CMBFAST) in their header to identify them.
The map simulation code synfast will issue a warning if the input power
spectrum file does not contain the keyword POLNORM, but no attempt will
be made to renormalize the power spectrum. If the keyword is present, it will be
inherited by the simulated map.
Eric Hivon
2010-06-18
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