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SWIRE Frequently-Asked Questions:

What does SWIRE stand for, and why?

SWIRE stands for Spitzer-space-telescope, Wide-field, InfraRed Extragalactic:

  • Spitzer Space Telescope because we are a project being carried out by NASA's Spitzer Space Telescope (formerly known as the Space Infrared Telescope Facility, the last of NASA "Great Observatories" space telescopes.
  • Wide-field is because we are the largest and widest survey to be done with the Spitzer Space Telescope. We will be looking at about 60 square degrees of sky. For comparison, the full moon is about 1/2 degree across and has an area of about 1/4 square degrees. Rather than looking for a long time at one place (which is what the GOODS program is doing), we are looking over a lot of the sky pretty quickly.
  • Infrared because we are carrying out the survey at wavelengths most sensitive to heat.
  • Extragalactic is because we are primarily interested in seeing things outside our own galaxy (another project, called GLIMPSE, is survey our Milky Way galaxy).

Folklore also holds that "SWIRE" stands for "Son of WIRE". In concept and design the SWIRE project is very similar to the WIRE project (a failed space mission), and most of the SWIRE science team are former members of the WIRE science team.

Why do you need to use the Spitzer Space Telescope, and not, say, a telescope on earth or the Hubble Space Telescope?

We have to use a space telescope because the wavelengths of light that we want to look at cannot penetrate the earth's atmosphere. Furthermore, looking in the infrared requires a special space telescope that is super-cold, because otherwise the heat from the telescope, instruments, and it's surroundings would be so bright as to blind it. It would be like trying to see the stars through a window from inside a room filled with bright lights. The Spitzer Space Telescope is designed specially to be able to do this. The instruments are cooled with liquid helium to just a few degrees above absolute zero. It is in an orbit which carries it away from the earth, which is a major heat source. It also has a "sunshade" which prevents sunlight from striking the telescope. While it is true that Hubble has an infrared instrument on-board (it is called "NICMOS"), it sees light that comes from objects that are around a thousand degrees, which is much hotter than the telescope! SWIRE is looking at objects that are just tens or hundreds of degrees Kelvin, which is anywhere from room temperature to 300 degrees below zero Fahrenheit!

Why a wide field?

There are two principal reasons for wanting to do a wide area survey. The first is that we know that galaxies and other distant objects are not distributed randomly on the sky. Instead, they appear as part of filaments or chains of galaxies (astronomers call this "large scale structure"). We believe this is related to how they formed. So, in order to see these chains we have to look at a very large area of sky, as these associations are quite large. The other reason has to do with rare objects. Many of the most interesting objects on the sky are interesting because there are so few of them. By looking over a very large area of the sky, we are much more likely to actually see some of these objects.

Why not look at the whole sky?

Looking at the whole sky would be great, but we can't. The instruments on the Spitzer Space Telescope are very sensitive, but their fields of view (the amount of sky they can see at one time) are very small, only about 1/6 the diameter of the full moon. Because they can only see a small amount of sky at once, it would take a very long time to do the whole sky. SWIRE is about the largest area of sky that the Spitzer Space Telescope could realistically survey.

Another satellite, IRAS, did survey the whole sky in the infrared in 1983. However, it could only see things that were 1000 times brighter than what SWIRE can see. Future missions, such as WISE and ASTRO-F will survey the entire sky in the infrared, but not with as much sensitivity as SWIRE.

Where will SWIRE look?

Most professional astronomers use a latitude/longitude system to describe where things are, which is different from how most amateur astronomers are used to thinking about the sky. If you want to see the "telephone numbers" for the SWIRE fields, look here. However, the SWIRE fields are located in:

ELAIS North 1Draco
ELAIS North 2Hercules
Lockman HoleUrsa Major
Chandra Deep Field SouthEridanus
ELAIS SouthPhoenix

If you click on the constellation name, you can see a finder chart, generated with XEphem. The white circle with the "X" in it denotes the location of the SWIRE field.

Why are you looking in more than one place?

We know that on average the universe looks about the same no matter where you look. However, if you look closely enough, there are differences between smaller areas. Astronomers call this "cosmic variance". An earthbound example might be if you looked at the daytime sky. On average it's all about the same. But if you just looked at a little bit of the sky, you might see clouds, or blue sky, or something in-between. The night sky is the same way. Since we can't look at the whole sky, just little pieces, we have chosen several different areas so that we can see, on average, what the sky looks like.

Who are you?

The SWIRE team is made up of many professional astronomers, including professors, post-docs, graduate students, undergraduates, and professional staff members such as programmers. Most of the team are located in Pasadena, California, at the Infrared Processing and Analysis Center, which is a division of JPL located on the Caltech campus, and various team members here work on other projects such as Spitzer Space Telescope, GALEX and 2MASS as well. Other team members are at Cornell University, the University of California in San Diego, NRAO, NOAO, and the Steward Observatory. A significant number of team members are located in Europe, specifically at Imperial College, the University of Sussex, and the Univerity of Wales in the U.K., CEA-Saclay in France, the University of Padova in Italy, and the IAC in Spain.

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by Dr. Carol Lonsdale and Dr. Russ Laher