Diffuse Observations with GALEX

Overview

The Galaxy Evolution Explorer (GALEX) was launched in 2003 and decomissioned in 2013. It has now observed most of the sky in two UV bands (FUV: 1526 Å and NUV: 2321 Å) with the data available at MAST. Although the original resolution was 5 - 10", the S/N is too low to extract the diffuse background at this resolution. I have therefore binned the data and masked out the stars to produce a tabulation of the diffuse background over the sky.
I have produced all-sky maps from these data and the FUV diffuse sky is shown on the left and the NUV diffuse sky is shown on the right. The FITS files from whence these images were produced may be downloaded by clicking on them.
Click to download FITS imageClick to download NUV FITS file.

Procedure and Details

There is a step by step procedure on how the data are processed from the original here. The publication is here with the ADS reference here. I have linked some of the more useful data and program files; others are available on request.

Data Location

The data are available as part of the STScI High Level Science Products (HLSP). The same data files are here.
File Name (Available from OneDrive)
 NLines
 Download Size (MB)
 Original Size (GB) (approx)
hlsp_uv-bkgd_galex_diffuse_glat90-80S_fuv-nuv_v1_table.txt
 2,196,993
 39.3
 0.3
hlsp_uv-bkgd_galex_diffuse_glat80-70S_fuv-nuv_v1_table.txt
 6,891,683
 122
 1.1
hlsp_uv-bkgd_galex_diffuse_glat70-60S_fuv-nuv_v1_table.txt
 11,117,124
 195
 1.7
hlsp_uv-bkgd_galex_diffuse_glat60-50S_fuv-nuv_v1_table.txt
 17,521,838
 304
 2.7
hlsp_uv-bkgd_galex_diffuse_glat50-40S_fuv-nuv_v1_table.txt
 16,406,149
 288
 2.6
hlsp_uv-bkgd_galex_diffuse_glat40-30S_fuv-nuv_v1_table.txt
 26,511,792
 456
 4.2
hlsp_uv-bkgd_galex_diffuse_glat30-20S_fuv-nuv_v1_table.txt 
21,512,539
 370
 3.5
hlsp_uv-bkgd_galex_diffuse_glat20-10S_fuv-nuv_v1_table.txt
 11,482,259
 203
 1.9
hlsp_uv-bkgd_galex_diffuse_glat10-00S_fuv-nuv_v1_table.txt
6,302,181
 109
 1.1
hlsp_uv-bkgd_galex_diffuse_glat00-10N_fuv-nuv_v1_table.txt
 6,370,046
 110
 1.1
hlsp_uv-bkgd_galex_diffuse_glat10-20N_fuv-nuv_v1_table.txt
 13,249,318
 234
 2.1
hlsp_uv-bkgd_galex_diffuse_glat20-30N_fuv-nuv_v1_table.txt
 16,422,219
 282
 2.6
hlsp_uv-bkgd_galex_diffuse_glat30-40N_fuv-nuv_v1_table.txt
 18,395,057
 314
 2.8
hlsp_uv-bkgd_galex_diffuse_glat40-50N_fuv-nuv_v1_table.txt
 18,917,725
 319
 2.9
hlsp_uv-bkgd_galex_diffuse_glat50-60N_fuv-nuv_v1_table.txt
 15,277,170
 258
 2.4
hlsp_uv-bkgd_galex_diffuse_glat60-70N_fuv-nuv_v1_table.txt
 10,857,896
 182
 1.7
hlsp_uv-bkgd_galex_diffuse_glat70-80N_fuv-nuv_v1_table.txt
 10,550,629
 182
 1.7
hlsp_uv-bkgd_galex_diffuse_glat80-90N_fuv-nuv_v1_table.txt
 2,408,038
 41.2
 0.4

Data Format


1
 Name String Name of the GALEX pipeline file
2
 Date String Observation date from GALEX pipeline file
3
 Time
 String Observation time from GALEX pipeline file
4
 FUV Exp. Time
 Integer Total exposure time in the FUV band
5
 NUV Exp. Time Integer Total exposure time in the NUV band
6
 X
 Integer Binned pixel in X
7
 Y
 Integer Binned pixel in Y
8
 GL Float Galactic Longitude
9
 GB Float Galactic Latitude
10
 ECL Float Ecliptic Longitude
11
 ECB Float Ecliptic Latitude
12
 ECL☉ Float Ecliptic Longitude of Sun
13
 ECB☉
Float Ecliptic Latitude of Sun
14
 FUVorig
Integer FUV flux from GALEX
15
 NUVorig Integer NUV flux from GALEX
16
 FUVAG Integer FUV airglow contribution
17
 NUVAG Integer NUV airglow contribution
18
 NUVZL Integer NUV zodiacal light contribution
19
 FUVFinal
Integer
Final FUV background
20
 NUVFinal Integer
 Final NUV background
21
 FUVMed
 Integer
 Median FUV background for the observation
22
 NUVMed
 Integer
Median NUV background for the observation
23
 FUVMin Integer
Minimum value for the FUV background across observations
24
 NUVMin
Integer
Minimum value for the NUV background across observations
25
 δFUV
 Integer
Standard deviation in FUV across observations
26
 δNUV
 Integer
Standard deviation in NUV across observations
27
100 μm
Float
 100 μm emission (MJy sr-1)-1
28
 E(B-V)
 Float
 E(B-V) (magnitudes)

Procedures to handle data (in IDL and GDL)

get_galex_hlsp_data.pro        : Read data files into structure for given coordinates.
create_wcs_map.pro              : Creates grid based on wcs parameters from data structure
get_galex_hlsp_telemetry.pro   : Reads GALEX telemetry data.

Other Data

GALEX position: I could not find an easy way to calculate local time from the GALEX data so I used the TLEs to derive the GALEX position as function of date. The data format is below and the actual local time for any observation may be interpolated from these values:
1
 Year
 Integer
 Year of Observation
2
 Month
Integer
 Month of Observation
3
 Day Integer
 Day of Observation
4
 Hour
Float
 Hour of Observation
5
 S/C Longitude Float
 Longitude of spacecraft on the Earth
6
S/C Longitude Rate
 Float
 Rate of change in longitude
7
 S/C Latitude
 Float Latitude of spacecraft on the Earth
8
 S/C Latitude Rate
 Float
 Rate of change in latitude

GALEX Foregrounds: I have tabulated the airglow and zodiacal light contributions to each of the observations (where one observation may be made up of multiple visits). The data format is as follows:
1
 File Name
String Root for GALEX observation
2
 Visits
 Integer
 Number of visits in the observation
3
 FUV Back
 Float Median value of foreground subtracted diffuse flux
4
 NUV Back
 Float Median value of foreground subtracted diffuse flux
5
 FUV AG Float
 Predicted airglow emission
6
 NUV AG
 Float
 Predicted airglow emission
7
 NUV ZL
 Float
 Predicted zodiacal light contribution