IRAS Explanatory Supplement
I. Introduction
C. Overview of Infrared Sky
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Figure I.C.1 Sky coverage of the IRAS Survey. Three plots of the entire
sky are shown with an equal area projection in equatorial coordinates
(see text). larger largest |
The various depths of coverage by the IRAS survey are displayed in
Fig. I.C.1. The clear areas in the middle plot
were covered with at least
two sets of confirming scans, while the clear areas in the bottom plot
were covered with confirming scans three or more times. Because the basic
requirement for inclusion in the IRAS catalogs was that an object had to
be observed with at least two sets of confirming scans, the clear portion
of the middle plot represents the basic area covered by the IRAS survey.
The shaded areas in the top plot show the areas of sky that were missed
entirely.
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Figure I.C.2 The distribution of IRAS sources with stellar
characteristics is shown in Galactic coordinates using an equal area
Aitoff projection. larger largest |
The general distribution of well-confirmed point sources observed by
IRAS is shown in Galactic coordinates in
Fig. I.C.2 to
I.C.4. Three classes
of source covering almost all objects in the point source catalog can be
defined according to spectral energy distribution: most of 130,000 sources
that are brighter at 12 µm than at 25 µm are stars
(Figure I.C.2); most of the 50,000 objects that
are brighter at 60 µm than at 25 µm and which are
located more than 20 degrees from the Galactic plane are external galaxies
(Fig. I.C.3); most of the 35,000 sources detected
only at 100 µm are cold, dense clumps within the interstellar cirrus
(Fig.I.C.4).
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Figure I.C.3 The distribution of IRAS sources selected to isolate external
galaxies is shown in Galactic coordinates in an equal area Aitoff projection.
Areas near the Galactic plane and in the Ophiuchus and Orion-Taurus regions
are heavily contaminated by Galactic objects. Galaxies detected only at
100 µm are discriminated against because of confusion
with the infrared "cirrus" shown in
Figure I.C.4 larger largest |
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Figure I.C.4 The distribution of IRAS sources detected only at
100 µm is shown in Galactic coordinates using an equal
area Aitoff projection. These sources are predominantly due to
emission from compact pieces of extended filamentary interstellar
dust structures, called infrared "cirrus". larger largest |