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Galactic pictures

10 July 2009

SPIRE images of the two galaxies showing long wavelength light emitted by dust in clouds where star formation is active. Significantly, the frames are also filled with many other galaxies which are much more distant and only show up as point sources.SPIRE images of the two galaxies showing long wavelength light emitted by dust in clouds where star formation is active. Significantly, the frames are also filled with many other galaxies which are much more distant and only show up as point sources.

Stunning "first-light" astronomical images have just been produced by a University-led instrument on board the Herschel Space Observatory.

On June 24 2009, the SPIRE instrument - a submillimetre camera and spectrometer designed and built by an international consortium led by scientists at the School of Physics and Astronomy - was able to observe the sky for the first time since its launch in May.

The telescope was trained on two galaxies called M66 and M74 to get a first impression of exactly what the instrument could see. The results were better than anyone expected from these ‘first-look’ observations, made before any attempt to set up the instrument or to tune the image-making software.

The SPIRE camera responds to light at wavelengths between 250 and 500 microns (500-1000 times longer than the wavelength of visible light). It is designed to look for long-wavelength light emitted from clouds of dust in regions where stars are forming in our own and other galaxies.

SPIRE image of M66 compared to a previous picture taken by NASA's Spitzer space observatory, illustrating the advances made by Herschel. (Spitzer images credit: NASA and the Spitzer SINGS team)SPIRE image of M66 compared to a previous picture taken by NASA's Spitzer space observatory, illustrating the advances made by Herschel. (Spitzer images credit: NASA and the Spitzer SINGS team)

The target galaxies showed up prominently, providing by far the best images yet seen at these wavelengths. Many other, more distant, galaxies were also seen in the field of view.

Professor Matt Griffin, School of Physics and Astronomy and SPIRE Principal Investigator, said: "These quick first light observations have produced dramatic results when we consider that they were made on day one. Astronomers planning to use SPIRE are delighted because they can see straight away that the main scientific studies planned with the instrument are going to work extremely well. In fact all three instruments on Herschel have now shown what they can do, and the results are spectacular all round."

The images effectively show reservoirs of gas and dust that are ready to be turned into stars in the galaxies. In M66, a spiral galaxy located about 36 million light years away, the images show most of the dust is located in the centre of the galaxy, which is why these areas appear brighter.

SPIRE images of M74 compared to a previous picture taken by NASA's Spitzer space observatory. (Spitzer images credit: NASA and the Spitzer SINGS team)SPIRE images of M74 compared to a previous picture taken by NASA's Spitzer space observatory. (Spitzer images credit: NASA and the Spitzer SINGS team)

In M74 a face-on spiral galaxy located about 24 million light years from Earth, SPIRE was able to trace the cold dust between the stars, and the spiral arms of the galaxy appear much more enhanced. They also contain many faint dots that are actually distant galaxies in the background.

Professor Steve Eales of the School, who will be working on the data from Herschel, said: "The big spiral galaxies are very beautiful but I was blown away by the hundreds of distant faint galaxies around M74. Now we've got to figure out what they tell us about the evolution of galaxies."

The images have given astronomers an exciting foretaste of the important scientific studies planned with SPIRE: the instrument will look at star formation close up in our own galaxy and in nearby galaxies, and it will search for star-forming galaxies in the very distant universe. Because these galaxies are so far away, their light has taken a very long time to reach us, so by detecting them the scientists will be looking into the past and learning how and when galaxies like the Milky Way were formed.

SPIRE images of M74 at three different wavelengths scaled to bring out the extended structure of the galaxy and to show more detail in the background sky.SPIRE images of M74 at three different wavelengths scaled to bring out the extended structure of the galaxy and to show more detail in the background sky.

Professor Peter Ade, of the School, who pioneered observations at these wavelengths and contributed to the design and build of the SPIRE instrument, said; "It is spectacular to see how far we have come from the first detections of extragalactic objects in the 1970’s with single-pixel instruments, to these marvellous images from the SPIRE cameras showing detail equivalent to the best ground based optical telescopes at that time."

Dr Peter Hargrave, also from the School, who led the SPIRE programme at Cardiff, said: "These images are absolutely stunning. It’s terrific payback for all the years of effort put into building such a great instrument."

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