Scientists advanced the new classification scheme today here at the 204th meeting of the American Astronomical Society (AAS).
"We have found that infrared light is a better way to classify galaxies," said Michael Pahre, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. Infrared images taken by the Spitzer Space Telescope can better dissect galaxies into their component parts the components being starlight, warm interstellar dust, and active nuclei, he said.
Hide and seek
Spitzers Infrared Array Camera (IRAC) has been tapped to discern the fundamental, physical differences among galaxies, Pahre told reporters. "This really points toward a new way of classifying galaxies using infrared."
Todays standard visual method of classifying galaxies stems from the work eight decades ago of astronomer Edwin Hubble. That method grouped galaxies according to their appearance in blue-light photographs.
Pahre said that the Hubble method misses what the Spitzer Space Telescope sees, thanks to the infrared observatorys ability to see structures hidden by dust.
New details
Information issued by the Harvard-Smithsonian Center for Astrophysics explains that elliptical and lenticular galaxies have lots of stars, but little dust or gas, and hence no current star formation activity. Spiral galaxies, on the other hand, have both stars and interstellar gas and dust, and they are continuously forming stars. The starlight seen in newly issued Spitzer images today appears blue, while the interstellar dust emission appears red.
For example, the NGC 5746 galaxy has been targeted by Spitzers IRAC. (see image ) Using different infrared wavelengths, the instrument has discerned the role that dust plays in obscuring starlight, as well as concealing a ring of warm dust.
The new detail "jumps out at you," Pahre added.
Totally unexpected
Spitzer infrared imagery also dealt scientists another surprise. Some galaxies previously placed in the elliptical/lenticular class were found to have warm dust faintly emitting from spiral arms. That finding was totally unexpected, Pahre noted.
Pahre said Spitzers space-based looks at galaxies outstrips ground-based telescopes.
The Keck Observatory, sitting on a remote outpost on the summit of Hawaii's dormant Mauna Kea volcano, takes a hundred-times longer to reach the same sensitivity as the Spitzer telescope, he said.
Over time, Spitzer will be imaging numbers of galaxies using its array of instruments. "So who knows what the future might bring," Pahre concluded.
The Jet Propulsion Laboratory (JPL) manages the Spitzer Space Telescope for NASA's Office of Space Science in Washington, D.C. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. JPL is a division of Caltech.
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