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Mapping the Infrared Universe Deeply

The Spitzer Wide-area Infra Red Extragalactic survey is one of six very large programs undertaken as Legacy surveys during the first year of the Spitzer Space Observatory. SWIRE has imaged nearly 50 square degrees (equal to the area of 250 full moons) divided among 6 different directions on the sky, detecting over 2 million galaxies by their heat radiation, some of them over 11 billion light years away.

As a survey, SWIRE's science goals are very broad and can encompass many different individual investigations. This large survey was designed with two general goals in mind. The first general goal of SWIRE is simply to observe a very large patch of sky with Spitzer, so that SWIRE can detect large numbers of galaxies across large expanses of space. Galaxies don't lie evenly across space, instead they are grouped into clusters, and clusters of clusters, or in long thin filaments, and there are large areas devoid of galaxies, called, imaginatively, voids. These structures can be extremely large across, so to map them out astronomers must chart vast areas, and that was what SWIRE was designed to do in the infrared with Spitzer. Galaxies have been charted across similar volumes before at other wavelengths, but in the infrared previous surveys have been much shallower, or much smaller. Why map galaxy structures? More...

SWIRE's second general goal is to detect galaxies far enough away that they can reveal how the Universe looked when it was 1/2 it's current age, or even younger. Since light travels at a finite speed, we see astronomical objects as they looked when the light set off, not as they are the moment that the light arrives at Earth. For the sun that time delay is only 8 minutes, but for the nearest galaxy it's over a million years! So doing astronomy is like using a time machine - to see things as they were a long time ago, just look further away! With SWIRE, we can see galaxies over 5 billion years old, or more.

We already knew from studies at other wavelengths that galaxies looked much different long ago than they do now, but we also knew that we would never fully understand them until we could observe them in the infrared (What's special about the infrared?). That's because many of their secrets are locked away from optical observatories, like the Hubble Space Telescope, because many early galaxies are full of great shrouds of dust which block optical and ultraviolet light from escaping; that's one of the key reasons that the Spitzer Space Telescope was designed and built.

So SWIRE charts millions of galaxies across vast reaches of space, reaching far away and back in time to see them as they were long ago. Many different science investigations can be done with this vast and unique collection of images and data.

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by Dr. Carol Lonsdale and Dr. Russ Laher