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pythonnumpyastronomyhealpy

Healpy default format for lmax


I found in the Healpy documentation that healpy.anafast has a default value for lmax of 3*nside-1

Is there a reason for this standard? Is it a standard within HEALPix, a standard for CMB experiments, or may it has physical reasons?

Edited: When I run anafast on a sky map Nside=4, the number of Cl values I get is of length = 12. That makes me think that lmax should be lmax=3Nside.

However, when using generated Cl values, the first two numbers are equal to zero: the monopole is zero, the dipole is zero.

Therefore, when I set the l values by np.arange(len(Clvalues)), should I also remove the terms [0,1] for the monopole and dipole?


Solution

  • Spherical harmonics discretized using HEALPix (either sampled at pixel centers, or avaraged over pixel areas) form a linearly independent system up to lmax = 3 nsmax -1. (from here: HEALPX anafast)