June 15, 2007 — Leave a comment

Wednesday’s seminar speaker was Robert Kennicutt, the principal investigator of the SINGS project (Spitzer Infrared Nearby Galaxies Survey). They have been using the Spitzer Space Telescope, launched 2003, to observe the dust content of the nearest galaxies.

Spitzer detects at a wide range of wavelengths in the infrared and submillimeter regimes. This is the part of the spectrum where a vast amount of the universe’s radiation is to be found. Dust absorbs starlight and remits it in this part of the spectrum. There is rather of a lot of dust around and so detecting at these wavelengths gives us valuable information about the structure of objects which may normally be either too bright or too dim to see clearly.

The telescope itself is an 85cm mirror which is cooled to 5.5K. The scope trails the Earth in its orbit around the Sun and is drifting away from the Earth at a rate of 0.1 AU per year. There are three instruments on board, which deliver a wide range of wavelength data. These are detailed as follows (info from Wikipedia).

  • IRAC (Infrared Array Camera), an infrared camera which operates simultaneously on four wavelengths (3.6 µm, 4.5 µm, 5.8 µm and 8 µm). The resolution is 256 × 256 pixels.
  • IRAS (Infrared Spectrograph), an infrared spectrometer with four sub-modules which operate at the wavelengths 5.3-14 µm (low resolution), 10-19.5 µm (high resolution), 14-40 µm (low resolution), and 19-37 µm (high resolution).
  • MIPS (Multiband Imaging Photometer for Spitzer), three detector arrays in the far infrared (128 × 128 pixels at 24 µm, 32 × 32 pixels at 70 µm, 2 × 20 pixels at 160 µm)

The best thing about Spitzer (if you ask me) is the multiple frequencies at which it can image objects in the sky. Shown above is a NASA press release image from Spitzer of the galaxy M81. As you move through the spectrum you are able to see levels of structure inside of the galaxy, which tells us a great deal about what it is made of and how its various parts interact. There are many beautiful images like this one, of several galaxies including the familar Andromeda Galaxy, M31.

I also wanted to share a particularly impressive example of this multiple wavelength instrument with the following image of the Triffid Nebula, M20. This first NOAO, visible light image shows the blue haze of the Triffid with its four, leaf-like segments glowing pinkish. The dark filaments which appear to divide up the lower part of the Triffid are obscuring fingers of dust blocking out the pink light from behind.

Now we can switch to Spitzer’s IRAC and MIPS instrument to see the dust instead. What you see in the greenish image below is the dust which previously was black. I find it particularly gratifying to see that you could almost fit the first image inside the second one. The shape of the original pink and blue clouds appeared carved out of this new version of the object. It seems that M20, as we know it, is indeed cacooned inside a larger conglomoration of dusty material, revealed here by Spitzer.

There is a direct comparison version of this JPEG to found here.

Absolutely incredible and there are many more images like this available. Wonderful! Well done to all the guys and gals working on Spitzer to give the world these fascinating pictures. Gosh that was a vertically-long post.

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