IRAS Sky Survey Atlas (ISSA) and Reject Fields

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The IRAS Sky Survey Atlas and Reject Fields are images of the sky as measured by IRAS at spatial scales larger than about 5'. The combination of calibration improvements and removal of most of the zodiacal emission results in a sensitivity limited by detector noise or confusion noise, at least for ecliptic latitudes more than 20° from the ecliptic plane. The ISSA images were designed to give relative photometry for objects outside the Solar system and do not give the absolute surface brightness of the sky.

The ISSA is comprised of 279 fields, 117 of which have centers at ecliptic mid-latitudes (50° > |beta| > 20°) and the remainder of which are at ecliptic latitudes above 50°. Complementary coverage (i.e., the ecliptic plane up to 20°) is provided by the 151 ISSA Reject fields, so called because the model used to subtract the zodiacal emission from them yields significant residuals. Each 500 by 500 pixel image, stored as a FITS file, covers a 12.5° x 12.5° square in gnomonic (tangent plane) projection with 1.5' x 1.5' pixels. For each field and IRAS band (12, 25, 60, and 100 microns), the ISSA and Reject Fields contain an intensity image for each confirming coverage (HCONs 1, 2, and 3) plus a coadded image (identified as HCON 0) of all the coverages.

The ISSA Explanatory Supplement cited below details several processing-related caveats to the interpretation of the images. These include slight intensity differences between neighboring plates at low ecliptic or Galactic latitude, the inclusion of a small amount of data near the Galactic plane with saturated 60 micron and 100 micron detectors, and some general, low-level artifacts due to imperfections in the model used to subtract the zodiacal intensities.

Note: The IRAS Sky Survey Atlas and Reject Fields are also available on CD-ROM. A special high-resolution set of maps for the 60 and 100 micron bands only has recently been released. The maps, which have angular resolution ~1', cover the Galactic latitude range |b| < 4.7° and selected regions at higher latitudes. IPAC offers an on-line interface for extracting images from this High Resolution IRAS Galaxy Atlas (IGA). The complete IGA, not yet available on-line here, may be ordered on tape or CD-R. Contact the Coordinated Request User Support Office (CRUSO) for more information. Depending on the affiliation of the requestor, a fee may be charged.

[More information is available in the Explanatory Supplement for the ISSA.]

Wheelock, S. L., et al., 1994, IRAS Sky Survey Atlas Explanatory Supplement, JPL Publication 94-11 (Pasadena: JPL)

Version and release date: 1991 Nov (|beta| > 50°); 1992 Dec (20 < |beta| < 50°); 1993 Feb (|beta| < 20°)

Sample ISSA FITS header

A service of the HEASARC and of the Astrophysics Science Division at NASA/GSFC
Goddard Space Flight Center, National Aeronautics and Space Administration
HEASARC Director: Dr. Andrew F. Ptak
LAMBDA Director: Dr. Thomas M. Essinger-Hileman
NASA Official: Dr. Thomas M. Essinger-Hileman
Web Curator: Mr. Michael R. Greason