HELP official SPIRE maps
========================

This product contains the homogenised SPIRE maps of the Herschel Extragalactic
Legacy Project.

## File structure

The FITS files have all the same structure with the Header Data Units (HDU)
listed below. If a kind of data is not available on a field, the corresponding
HDU is empty.

1. Primary HDU.
2. **IMAGE**: The signal map in *Jy/beam*.
3. **NEBFILT**: The signal map filtered for nebular emission by the *nebular*
    software from Casutools (see *dmu19_nebular_filtered_maps*).
4. **ERROR**: The error map in *Jy/beam*.
5. **EXPOSURE**: The exposure map in *seconds*.
6. **MASK**: The mask map with the following values:
    - 0: no mask (*i.e.* good data);
    - 1: regions with low depth relative to the rest of the map.

### Fixme

The `hers-helms-xmm_itermap_20160623_PSW.fits` is corrupted and we can only
access the first HDU with the image map. I checked with Marco and the file is
also corrupted on Caltech servers. Someone should recreate the maps with only
the Herschel-Stripe-82 ObsIDs (i.e. without XMM-LSS, to get smaller files).

### Notes

- Some original maps does not contain exposure information but coverage maps
  expressed in number of hits.  These coverage maps where converted to exposure
  multiplying the hit value by 1/10 s for parallel mode and 1/18.6 s for
  standard observations.
- We may want to add point filtered maps.
- The different ways of computing error between projects should be described.
- The mask definition is not exactly the same between surveys. For H-ATLAS, it
  only which pixels were observed or not. AKARI-NEP does not provide masks.

## Lists of Herschel Observation identifiers (ObsIDs)

The Herschel observation identifiers (ObsIDs) used in each map are provided in
the headers of the primary HDU.  We also provide to list of ObsIDs relevant for
HELP.

### `HELP_ObsIDs_SPIRE.xls`

This files contains the list of the ObsIDs associated to HELP.  It is based on
the list produced by Seb, with a addition of the ObsIDs for AKARI-NEP and
SPIRE-NEP given by Chris.

- Some observation have a “failed” QC_status (in red in the spreadsheet) and are
    not available.
- The observation for *COSMOS_CANDELS* and *CANDELS_UDS-1* (in orange) are in
    the primary list of ObsIDs but are not used in HELP data products.
- We have to check with H-ATLAS to be sure they used all the ObsIDs in this
    list.
- There is a column “In_HELP” set to true for the ObsIDs actually used for HELP
    maps.
- When producing the big Herschel-Stripe-82 + XMM-LSS map, some observations
    were forgotten, the column “Missing_from_HS82_XMM” is true for them.

### `All_SPIRE_ObsIDs_on_HELP_coverage.fits`

This is the list of all the SPIRE ObsIDs queried from the Herschel Science
Archive (at the begining of October 2017) and limited to HELP coverage.