Knowledgebase
What is the format of the CMB maps produced by the SMICA component separation code?
Posted by Peregrine McGehee on 12 August 2013 02:20 PM

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
COM_CompMap_CMB-smica_2048_R1.20.fits

; 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]

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