Knowledgebase: Planck

Planck Documentation

All the Planck documentation can be found linked from here. There is information for each delivery. Note that the PDF version misses some figures and references compared to the wiki.

Planck Canonical Papers

All the Canonical papers can be found linked from here. There is a paper for each delivery.

Why do I see negative values in Planck intensity and covariance maps?

While both the intensity and covariance quantities presented in the Planck all-sky maps are, by definition, positive, there are situations in which you will see negative values.

First, in regards to the Planck intensity maps: The Planck all sky intensity maps do not have the Cosmic Microwave Background (CMB) subtracted. The CMB subtracted maps can be found together with the component separated CMB maps, for example at: However, negative values in intensity (but not covariance) can occur because of noise.

Second, in regards to the Planck covariance maps: Covariance values should not be negative. The negative values in the covariance are HEALPix bad values, i.e., -1.63750E+30. That being said, the covariance in some of the maps are plotted in units of log(II_COV) which could be negative even if the number is positive.

Here is an example in IDL based on the 100 GHz (R1.1) map in Data Release 1 called HFI_SkyMap_100_2048_R1.10_nominal.fits:
HIDL> gb = where(m.ii_cov ne !healpix.bad_value)
HIDL> print, minmax((m.ii_cov)[gb]) ; this is only the valid pixels
% Compiled module: MINMAX.
1.20344e-11 1.38910e-07
HIDL> print ,minmax(m.ii_cov) ; this is all pixels including the pixels with no coverage which have the healpix bad value
-1.63750e+30 1.38910e-07

What are the intensity units of the Planck all-sky maps and how do I convert between them?

The Planck map products express intensity in three different (and frequency-dependent) forms: K_CMB (thermodynamic temperature), K_RJ (antenna temperature, also know as Rayleigh-Jeans temperature), and MJy/sr. The memo addresses the definition of these quantities and the conversions between them.

What is the format of the CMB maps produced by the SMICA component separation code?

The SMICA maps are multi-extension FITS files containing the CMB (in the 1st extension) then the residuals at each band in the 2nd and 3rd extensions. The CMB units are uK_CMB as stated in the headers. For 30-353 GHz the map residuals are map-CMB = foregrounds in K_CMB. For 545 and 857 GHz the residuals are in MJy/sr.

Here is how the file is read in IDL. The (Nside=1024) LFI maps are in the 2nd extension and the (Nside=2048) HFI maps are in the 3rd extension.

HIDL> fn = findfile('COM*fits')
HIDL> print, fn

; Reading in the CMB map

HIDL> read_fits_s, fn, xp, x0, extension=0
File size (MB) 720.000
HIDL> help, x0
** Structure <17f4e928>, 7 tags, length=754975760, data length=754975760, refs=1:
HDR STRING Array[65]
I FLOAT Array[50331648]
NOISE FLOAT Array[50331648]
VALMASK BYTE Array[50331648]
I_MASK BYTE Array[50331648]
INP_CMB FLOAT Array[50331648]
INP_MASK BYTE Array[50331648]

; Reading in the residual maps for the LFI bands

HIDL> read_fits_s, fn, xp, x1, extension=1
File size (MB) 144.000
HIDL> help, x1
** Structure <17f21be8>, 4 tags, length=150995776, data length=150995776, refs=1:
HDR STRING Array[52]
LFI_030 FLOAT Array[12582912]
LFI_044 FLOAT Array[12582912]
LFI_070 FLOAT Array[12582912]

; Reading in the residual maps for the HFI bands

HIDL> read_fits_s, fn, xp, x2, extension=2
File size (MB) 1152.00
HIDL> help, x2
** Structure <17f21328>, 7 tags, length=1207960528, data length=1207960528, refs=1:
HDR STRING Array[61]
HFI_100 FLOAT Array[50331648]
HFI_143 FLOAT Array[50331648]
HFI_217 FLOAT Array[50331648]
HFI_353 FLOAT Array[50331648]
HFI_545 FLOAT Array[50331648]
HFI_857 FLOAT Array[50331648]