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The Wide-field Infrared Survey Explorer at IPAC |
You are strongly encouraged to read the Explanatory Supplement to the WISE All-Sky Data Release Products before using WISE Image and Source Catalog and Database information. In particular, please familiarize yourself with the Cautionary Notes section of the Supplement to make best use of the WISE data products.
Access modes for the WISE image and tabular data products are described in section I.3 of the WISE Explanatory Supplement.
The WISE All-Sky Release Source Catalog is available for bulk download via the NASA/IPAC Infrared Science Archive. The download version is in compressed ascii format and is organized into 50 separate files. You will need 280GB of storage space available to download the compressed Catalog files, and approximately 864GB to store the full uncompressed, ascii Catalog.
The WISE filter bandpasses are described in section IV.4.h.v of the WISE Explanatory Supplement. The filter bandpass relative spectral response (RSR) curves are shown graphically in Figures 4a and 4b, and can be downloaded in ASCII table format from links in the captions to those two figures.
WISE Catalog and Single-exposure Source Database magnitudes are given in the Vega system and represent total in-band brightness measurements. Conversion of WISE in-band magnitudes to monochromatic values such as flux density or AB magnitude, along with some helpful examples, are described in section IV.4.h.i of the WISE Explanatory Supplement. The broad WISE bandpasses may require applying significant color corrections when deriving monochromatic brightnesses depending on the spectral energy distribution of the particular object. The nominal system flux zero points are defined for a fν∝ν-2 spectrum through the WISE bandpasses. Color corrections for other spectral slopes are given in section IV.4.h.vi of the Supplement.
WISE Source Catalog profile-fit magnitudes
(w?mpro)
and the curve-of-growth corrected "standard" aperture magnitudes
(w?mag)
systematically underestimate the brightness of sources that are resolved
with respect to the WISE PSF. Sources whose shapes are complex and/or
or extended with respect to the PSF are identified in the Catalog
by having extended source flag
(ext_flg) values greater than zero.
For WISE sources that are resolved and are associated with 2MASS Extended
Source Catalog (XSC) sources, ext_flg=5, you may wish to use
the elliptical aperture photometry measurements,
w?gmag,
that are made using apertures scaled from the 2MASS XSC shape values.
These measurements do a better job of capturing the total source
brightness, but may still underestimate it slightly, as described in
section VI.3.e of the WISE Explanatory Supplement.
If a WISE source is associated with a 2MASS XSC object but is not
resolved (ext_flg=4), then the elliptical aperture magnitudes
will overestimate the true brightness. Use the profile-fit magnitudes instead.
For WISE sources that are extended but not associated with a 2MASS XSC
objects, you may examine the large aperture magnitudes in the
WISE Source Catalog. These measurements do not have any aperture corrections
applied so do not make any assumption about source compactness.
Links to gzip'd tar files that contain images of the 9x9 grid of
PSFS in each band used for profile-fitting source extraction have been added
to section IV.4.c.iii.1 of the
Explanatory Supplement.
The WISE Atlas Image pixel values cannot be converted directly to calibrated absolute surface brightness levels for two reasons. First, the absolute instrumental dark-current level in each WISE exposure could not be accurately estimated and tracked. Second, the Single-exposures contributing to each Atlas Image have their background-levels matched to an average local value during the coaddition process to minimizing relative offsets in their overlap regions only. The resulting background levels (in DN/pixel) were not placed on a scale that could be converted to absolute surface-brightness units. Consequently, the Atlas (and Single-exposure) Images are designed for relative photometric measurements where the brightness is measured with respect to the local sky background. Instructions for making photometric measurements with the Atlas Images are given in section II.3.f of the Explanatory Supplement.
Measurements of objects in the WISE All-Sky Release Source Catalog are extracted from multiple, independent observations taken at different times. The earliest, latest and average Modified Julian Dates of the observations used in each band for a Catalog source entry are given in the w?mjdmin, w?mjdmax, and w?mjdmean columns (where ?=1,2,3 or 4 for each WISE band). Note that you will need to select the Catalog "Long Form" when using the IRSA/GATOR Catalog Search service service to see the w?mjdmin, w?mjdmax, and w?mjdmean columns.
The Modified Julian Date of the observations of objects detected in the individual WISE exposures is given in the mjd column of the WISE Single-exposure Source Working Database.
No quality filters were applied to the 2MASS PSC entries before positionally associating them with the WISE Source Catalog and Single-exposure Source Database entries. Associations were made with the full composite 2MASS All-Sky PSC, that includes the high reliability Catalog and the lower signal-to-noise extension (see section I.6.b.i of the 2MASS All-Sky Data Release Explanatory Supplement).
Last update - 2014 April 11 Contact the WISE Help Desk
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