For the first time, the general public will be able to browse detailed infrared images of more than 200 galaxies. The pictures, originating from data from the orbiting Spitzer Space Telescope, will be released later this year. Dr George Bendo of the Jodrell Bank Centre for Astrophysics will highlight the new imagery in a preview at the National Astronomy Meeting in Manchester.
The mid-infrared (24 micron) image of M91 as seen with the Spitzer Space Telescope. M91 is the prototype example of a barred spiral galaxy. Although the spiral arms are easily seen in mid-infrared light, the bar is only faintly visible.
NGC 4772 contains a dust ring that is bright in mid-infrared light. Dust rings like this are common in many spiral galaxies.

These galaxies is just two of the over 200 galaxies for which reprocessed Spitzer Space Telescope data are being released to the general public for the first time.
The pictures are mid-infrared (24 micron wavelength) reprocessed images of nearby galaxies observed with Spitzer between 2003 and 2009. Amongst the images are the galaxies M60, M61, M88, M91 and M98, all of which lie between 47 and 63 million light years away in the large cluster of galaxies found in the direction of the constellation of Virgo.
M60 is actually two galaxies that appear next to each other in the sky but are actually physically separated from each other. The larger elliptical galaxy looks relatively faint and contains little dust to produce mid-infrared light, but the smaller spiral galaxy contains a lot of dust and looks much brighter.
The mid-infrared light from these galaxies primarily traces interstellar dust heated by the hot young stars found in the places where stars are forming. The images, which are being made available to the public for the first time, are a small sample of those that will be released later in the year.
M61 is one of the larger spiral galaxies in the Virgo Cluster. The spiral arms and the nucleus in this galaxy are both locations where many hot young stars are forming. These stars heat up the interstellar dust that looks very bright in mid-infrared light.

Dr Bendo explains how complicated it was to make the data usable for science. “The 24-160 micron Spitzer images need expert processing to be suitable for scientists, let alone the general public and until now many of them had been overlooked. I volunteered to do this work for these galaxies as they will soon be observed by the Herschel Space Observatory at far-infrared wavelengths. With processed Spitzer data, astronomers will be able to make a direct comparison between the views from each telescope.”
M88 is currently underoing a process where the interstellar gas and dust in the galaxy are colliding with gas between the galaxies in the Virgo Cluster. This process will eventually strip away much of the gas and dust in the galaxy.
He is delighted to be bringing the Spitzer material to the public: “These data show the intimate connection between the interstellar dust in galaxies, here seen shining in infrared light, and the formation of stars on a grand scale. Now anyone with Internet access can download these extraordinary pictures for themselves and take a look at some of the objects being studied by the world’s leading astronomers, as part of their effort to better understand the universe we live in.”
NGC 4298 and NGC 4302 both appear close to each other in sky but are actually further apart than implied by this image. Both of these galaxies are located in the Virgo Cluster and are falling towards the centre of the cluster.
NGC 4698 is another spiral galaxy with a very well-defined dust ring. The centre of the galaxy contains an active galactic nucleus. Astronomers hypothesize that such active galactic nuclei contain supermassive black holes. While the black hole itself would produce no light, the region around the black hole can very very bright and could be producing the infrared light seen from the centre of this galaxy.
Contacts and sources:
Dr Robert Massey
Royal Astronomical Society
The scientific data are available from:
http://hedam.oamp.fr/
ttp://www.jb.man.ac.uk/~gbendo/exchange/SpitzerData/spitzerdata_main.html