Sky temperature maps

Introduction

Sky maps are produced by combining appropriately the data of all working detectors in a frequency channel over some period of the mission. They give the best estimate of the signal from the sky (unpolarised) after removal, as far as possible, of known systematic effects and of the dipole signals induced by the motion of the solar system in the CMB and of the Planck satellite in the solar system. In particular, they include the Zodiacal light emission (Zodi for short) and also the scattering from the far-side lobes of the beams (FSL). More on this below.

Sky maps are provided for the nominal Planck mission and for the first two single surveys, the third one being covered only for a small part during the nominal mission (REF). AMo: There is a table with table below that defines these coverage periods, but I believe that information should be in an earlier section that describes the mission and the events that interrupted it, the planet passages, the pointing, issues relating to timing, etc. That section should define a pointing period, and operational day, etc. There is some of that info in the HFI pre-processing section, but that may not be the best place for it.For characterization purposes, are also provided maps covering the nominal survey but using only half of the available data. These are the ringhalf_{1|2} maps, which are built using the first and second half of the stable pointing part of the data in each pointing period.

Missions and sky survey coverage periods

Name	Ini_OD	Ini_Ring	Ini_ptgID	End_OD	End_ring	End_ptgID
Nominal	91	240	00004200	563	14724	03180200
HFI-Full	91	240	00004200	993	27008	06344800
LFI-Full	91	240	00004200	TBD	TBD	TBD
SCAN1	91	240	00004200	270	5720	01059820
SCAN2	270	5721	01059830	456	11194	02114520
SCAN3	456	11195	02114530	636	16691	03193660
SCAN4	636	16692	03193670	807	21720	04243900
SCAN5	807	21721	95000020	993	27008	06344800
SCAN6	993	----	06344810	993	----	TBD

All sky maps are in Healpix format, with Nside of 2048 for HFI and of 1024 for LFI, in Galactic coordinates, and Nested ordering. The signal is given in units of K_cmb for 33-353 GHz, and of MJy/sr (for a constant $\nu F_\nu$ energy distribution ) for 545 and 857 GHz. Each sky map is packaged into a BINTABLE extension of a FITS file together with a hit-count map (or hit map, for short) and a variance map, and additional information is given in the FITS file header. The structure of the FITS file is given in the FITS file structure section below.

The FITS filenames are of the form {H|L}FI_SkyMap_fff_nnnn_R1.nn_{type}_{coverage}_{type}.fits, where fff are three digits to indicate the Planck frequency band, and nnnn is the Healpix Nside of the map, coverage indicates which part of the mission is covered, and the optional type indicates the subset of input data used. A full list of products, by their names, is given in the List of products below.

HFI processing

The mapmaking pipeline is described in detail in the Map-making section, and a brief summary is given here for convenience.

The cleaned TOIs of signal of each detector, together with their flags, and the TOIs of pointing (quaternions), are the inputs to the mapmaking step. The input signal TOIs are calibrated in Watt, and their associated flags are used to samples or full rings to discard. Are discarded periods of unstable pointing and pointing maneuvers in general, glitched data, transits over bright planets (and some asteroids TBC) (since they move, the hole is covered during another sky survey), and some full rings are discarded if their noise properties differ significantly from the nominal value and the few rings of duration longer than 90 min, since the pointing is not sufficiently stable over such long periods (details in Discarded rings section). The TOIs are first used to build Healpix rings, each ring containing the combined data of one pointing period using the nearest grid point method (NGP). These are then calibrated in brightness, cleaned of the dipole signals, and projected onto Healpix maps as explained in the following sections. Need to add POINTING DETAILS

The cleaned TOIs are expressed in Watts from the sky absorbed by the bolometer and must be calibrated in astrophysical units. At 100-353 GHz, the flux calibration gains are determined for each pointing period (or ring) from the solar-motion dipole after removal of the small dipole induced by the motion of the Planck satellite in the solar system. The solar-motion dipole from WMAP (REF) is used for this purpose. This gain by ring is then smoothed with a window of width 50 rings, which reveals an apparent variation of ~1-2% on a scale of 100s to 1000s of rings for the 100-217 GHz channels, and is applied to the Watt data. At 353GHz, where the solar motion dipole is weaker compared to the signal, no gain variation is detected, and the same fixed gain is applied to all rings. At 545 and 857 GHz the gain is determined from the observation of Uranus and Neptune (Jupiter is not used because its brightness produced some non-linearity in the bolometer response) and comparison to recent models (REF) made explicitly for this mission. A single gain is applied to all rings at these frequencies.

Prior to projecting the Healpix rings (HPRs) onto a map, a destriping approach is used to remove low-frequency noise. The noise is modelled as the sum of a white noise component and a constant, or offset, per pointing period which represents the low frequency 1/f noise. The offsets are determined by minimizing the differences between HPRs at their crossings. After subtracting these offsets, calibrated data are projected onto Healpix maps, with the data of each bolometer weighted by a factor of 1/NET of that bolometer.

These maps provide the main mission products. A second, reduced, set of maps, cleaned of the Zodiacal emission of the FSL leakage is also produced for the nominal mission and the two single surveys, but not for the half-rings. For this purpose, the the Zodiacal emission and the FSL contamination, which are not fixed on the sky, are modeled separately at HPR-level, and subtracted from the signal HPR before projecting them onto the maps.

Together with signal maps, hit count and variance maps are also produced. The hit maps give the (integer) number of valid TOI-level samples that contribute to the signal of each pixel. All valid samples are counted in the same way, i.e., there is no weighting factor applied. The variance maps project the white noise estimate, provided by the NETs, in the sky domain.

LFI processing

LFI processing is covered in Sect. 4.5

Selected images

Insert here some images:

Types of maps

Full channel maps

Full channel maps are built using all the valid detectors of a frequency channel and cover the full mission (or the nominal mission for the 1st release). For HFI, the 143-8 and 545-3 bolometers are rejected entirely as they are seriously affected by RTS noise.

Single survey maps

Single survey maps are built using all valid detectors of a frequency channel, but cover separately the different sky surveys. The single sky surveys are defined in terms of the direction of the satellite's spin axis: the first survey covers from the beginning of the science observations (the First Light Survey) to the time when the spin axis has rotated by 180 degrees (to the nearest pointing period), the following ones covers from 180 to 360, and so on. In the case of the nominal mission, the process stops at the third survey, which is incomplete. In the case of the full mission the 4th survey was interrupted shortly before completing the 180 degree rotation (see LINK), in order to begin observing with a different scanning law. The HFI mission ended slightly before the natural end of the 5th survey, the LFI mission continued to the XXX survey. The coverage of each of these periods in terms of ring number, pointingID, and OD, is given in the table below. Note that the OD numbers are only to indicate during which OD the period boundary occurs.

Half-ring maps

Half-ring maps are built using only the first or the second half of the stable pointing period data. There are thus two half-ring maps per frequency channel named ringhalf_1 and ringhalf_2 respectively. These maps are built for characterization purposes in order to perform null tests. In particular, the difference between the two half-ring maps at a given frequency give a good estimate of the high frequency noise in the data.

Caveats and known issues

The Zodiacal light and the Far-Side Lobes

Insert here how these are seen in the differences of the single survey maps

Artifacts near caustics of the scanning strategy

TBW if still an issue??

List of products

The list of products containing sky maps are given below, grouped by type

Outstanding: link to archive objects / LFI to fill in their products

Full channel maps 

LFI maps ….
HFI_SkyMap_100_2048_R1.nn_nominal.fits
HFI_SkyMap_143_2048_R1.nn_nominal.fits
HFI_SkyMap_217_2048_R1.nn_nominal.fits
HFI_SkyMap_353_2048_R1.nn_nominal.fits
HFI_SkyMap_545_2048_R1.nn_nominal.fits
HFI_SkyMap_857_2048_R1.nn_nominal.fits

Single survey maps 

LFI maps ….
HFI_SkyMap_100_2048_R1.nn_survey_1.fits
HFI_SkyMap_143_2048_R1.nn_survey_1.fits
HFI_SkyMap_217_2048_R1.nn_survey_1.fits
HFI_SkyMap_353_2048_R1.nn_survey_1.fits
HFI_SkyMap_545_2048_R1.nn_survey_1.fits
HFI_SkyMap_857_2048_R1.nn_survey_1.fits
HFI_SkyMap_100_2048_R1.nn_survey_2.fits
HFI_SkyMap_143_2048_R1.nn_survey_2.fits
HFI_SkyMap_217_2048_R1.nn_survey_2.fits
HFI_SkyMap_353_2048_R1.nn_survey_2.fits
HFI_SkyMap_545_2048_R1.nn_survey_2.fits
HFI_SkyMap_857_2048_R1.nn_survey_2.fits

Half-ring maps 

LFI maps ….
HFI_SkyMap_100_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_143_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_217_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_353_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_545_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_857_2048_R1.nn_nominal_ringhalf_1.fits
HFI_SkyMap_100_2048_R1.nn_nominal_ringhalf_2.fits
HFI_SkyMap_143_2048_R1.nn_nominal_ringhalf_2.fits
HFI_SkyMap_217_2048_R1.nn_nominal_ringhalf_2.fits
HFI_SkyMap_353_2048_R1.nn_nominal_ringhalf_2.fits
HFI_SkyMap_545_2048_R1.nn_nominal_ringhalf_2.fits
HFI_SkyMap_857_2048_R1.nn_nominal_ringhalf_2.fits

Zodi and Far-side-lobes corrected maps 

HFI_SkyMap_100_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_143_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_217_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_353_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_545_2048_R1.nn_nominal_ZodiCorrected.fits
HFI_SkyMap_857_2048_R1.nn_nominal_ZodiCorrected.fits

HFI_SkyMap_100_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_143_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_217_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_353_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_545_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_857_2048_R1.nn_survey_1_ZodiCorrected.fits
HFI_SkyMap_100_2048_R1.nn_survey_2_ZodiCorrected.fits
HFI_SkyMap_143_2048_R1.nn_survey_2_ZodiCorrected.fits
HFI_SkyMap_217_2048_R1.nn_survey_2_ZodiCorrected.fits
HFI_SkyMap_353_2048_R1.nn_survey_2_ZodiCorrected.fits
HFI_SkyMap_545_2048_R1.nn_survey_2_ZodiCorrected.fits
HFI_SkyMap_857_2048_R1.nn_survey_2_ZodiCorrected.fits

---

A comment from E. Keihänen:

Here is a list of things that should go into this section:

• Insert a table of maps delivered:
  • file name
  • radiometers included
  • PID/OD range
  • resolution
  • (-polarization included or not)
  • sky coverage
  • baseline length
  • -reference to input toi objects)
• Explain the format of the files, what is in what column, in what units.
• Information common for all LFImaps:
  • LFI maps were constructed with the Madam map-making code (version 3.7.4).
  • Maps are in Healpix format, in nested pixeling scheme, in K_cmb units, and in galactic coordinate system.
  • Unobserved pixels are marked by the special value -1.6375e30.

---

EK's comment ends

FITS file structure

The FITS files for the sky maps contain a simple primary header with no data, and BINTABLE extension (EXTENSION 1, EXTNAME = 'FREQ-MAP') containing the data. The structure is shows schematically in the figure below.

FITS file structure

The primary header has the form

;-----------------------------------------------------------------------------
; EXTENSION 0: 
; - Header
;-----------------------------------------------------------------------------
MRDFITS: Null image, NAXIS=0
SIMPLE  =                    T /Dummy Created by MWRFITS v1.11                  
BITPIX  =                    8 /Dummy primary header created by MWRFITS         
NAXIS   =                    0 /No data is associated with this header          
EXTEND  =                    T /Extensions may (will!) be present               
END                                                                             
  

The FREQ-MAP BINTABLE extension contains the data. The table contains 3 columns of that contain the signal, variance, and hit-count maps in Healpix format. the number of rows is 50331648 for HFI and 12582912 for LFI, corresponding to the number of pixels in a Healpix map of Nside= 2048 and 1024, respectively (N.B: Npix = 12 Nside^2). The 3 columns are I_STOKES for the intensity (or temperature) signal, II_COV for the variance, and HIT for the hit-count. The exact order of the columns in the figure is indicative only, and the details can be found in the keywords. Keywords also indicate the coordinate system (GALACTIC), the Healpix ordering scheme (NESTED), the units (K_cmb or MJy/sr) of each column, and of course the frequency channel (FREQ). The COMMENT fields give a one-line summary of the product, and some other information useful for traceability within the DPCs. The original filename is also given in the FILENAME keyword as is the md5 checksum for the extension. The BAD_DATA keyword gives the value used by Healpix to indicate pixels for which no signal is present (these will also have a hit-count value of 0).

A typical header for the data extension of an intensity only map is:

;-----------------------------------------------------------------------------
; EXTENSION 1: FREQ-MAP
; - Header
;-----------------------------------------------------------------------------
MRDFITS: Binary table.  3 columns by  1 rows.
XTENSION= 'BINTABLE'           /Written by IDL:  Thu Jan 31 11:03:21 2013       
BITPIX  =                    8 /                                                
NAXIS   =                    2 /Binary table                                    
NAXIS1  =            603979776 /Number of bytes per row                         
NAXIS2  =                    1 /Number of rows                                  
PCOUNT  =                    0 /Random parameter count                          
GCOUNT  =                    1 /Group count                                     
TFIELDS =                    3 /Number of columns                               
COMMENT                                                                         
COMMENT  *** End of mandatory fields ***                                        
COMMENT                                                                         
EXTVER  =                    1 /Extension version                               
DATE    = '2013-01-31'         /Creation date                                   
COMMENT                                                                         
COMMENT  *** Column names ***                                                   
COMMENT                                                                         
TTYPE1  = 'I_STOKES'           /                                                
TTYPE2  = 'HITS    '           /                                                
TTYPE3  = 'II_COV  '           /                                                
COMMENT                                                                         
COMMENT  *** Column formats ***                                                 
COMMENT                                                                         
TFORM1  = '50331648E'          /                                                
TFORM2  = '50331648J'          /                                                
TFORM3  = '50331648E'          /                                                
COMMENT                                                                         
COMMENT  *** Column units ***                                                   
COMMENT                                                                         
TUNIT1  = 'K_CMB   '           /                                                
TUNIT2  = '        '           /                                                
TUNIT3  = 'K_CMB   '           /                                                
COMMENT                                                                         
COMMENT  *** Planck params ***                                                  
COMMENT                                                                         
EXTNAME = 'FREQ-MAP'           / Extension name                                 
COORSYS = 'GALACTIC'           / Coordinate system                              
ORDERING= 'NESTED  '           / Healpix ordering                               
NSIDE   =                 2048 / Healpix Nside                                  
FIRSTPIX=                    0 / First pixel # (0 based)                        
LASTPIX =             50331647 / Last pixel # (0 based)                         
FILENAME= 'HFI_SkyMap_217_2048_R1.10_nominal_ZodiCorrected.fits' / FITS filename
CHECKSUM= '3aIB6Z993aGA3Y99'   / HDU checksum created 2013-01-31T10:03:22       
BAD_DATA=         -1.63750E+30 / bad pixel value                                
FREQ    = '217     '           / reference frequency                            
PROCVER = 'DX9_Delta'          / Product version                                
COMMENT                                                                         
COMMENT ------------------------------------------------------------------------
COMMENT Full channel sky map: nominal mission, corrected for Zodi & FSL         
COMMENT ------------------------------------------------------------------------
COMMENT HFI-DMC objects:                                                        
COMMENT in-group: MAP_v53_noZodi_2048_GALACTIC_0240_27008/                      
COMMENT Creation date  - object name                                            
COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_I                           
COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_H                           
COMMENT 13-01-03 18:33 - 217GHz_W_TauDeconv_nominal_II                          
COMMENT ------------------------------------------------------------------------
END                                                                             

The same structure applies to all SkyMap products, independent of whether they are full channel, survey of half-ring. The distinction between the types of maps is present in the FITS filename (and in the traceability comment fields).