Feature: Cosmic Suburbia is a Better Breeding Ground for Stars

Cosmic Suburbia is a Better Breeding Ground for Stars

New observations from NASA's Spitzer Space Telescope suggest that galaxies
prefer to raise stars in cosmic suburbia rather than in "big cities."

Galaxies across the universe reside in cosmic communities, big and small. Large,
densely populated galactic communities are called galaxy clusters. Like big cities
on Earth, galaxy clusters are scattered throughout the universe, connected by a
web of dusty "highways" called filaments. While thousands of galaxies live
within the limits of a cluster, smaller galactic communities are sprinkled along
filaments, creating celestial suburbs. Over time, astronomers suspect that all
galactic suburbanites will make their way to a cluster by way of filaments.

For the first time, Spitzer's supersensitive eyes have caught an infrared glimpse of
several galaxies traveling along two filamentary roads into a galaxy cluster called
Abell 1763.

"This is the first time we've ever seen a filament leading into a cluster with an
infrared telescope," says Dario Fadda, of the Herschel Science Center, which is
located at the California Institute of Technology in Pasadena, Calif.

"Our observations show that the fraction of starburst galaxies in the filaments is
more than double the number of starburst galaxies inside the cluster region," he
adds.

According to Fadda, clusters and the filaments that connect them are among the
largest structures in the cosmos. To see them, astronomers need instruments that
can map large areas of sky and have the sensitivity to resolve individual galaxies.

Luckily, instruments aboard Spitzer can do both. Using the telescope's multiband
imaging photometer, Fadda and his colleagues saw structures spanning 23 million
light-years. They used the observatory's infrared array camera to collect a census
of each galaxy's star formation and used a ground-based telescope at the Kitt Peak
National Observatory near Tucson, Ariz., to determine which galaxies belonged
to the cluster and surrounding filaments. Ultimately, Fadda found that galaxies in
the filaments form stars at a higher rate than their cluster counterparts.

"The new Spitzer findings will provide valuable insights into how galaxies grow
and change as they leave cosmic suburbia for the big cities," says Fadda.

He notes that future infrared missions will be able to follow in Spitzer's footsteps
and study how filaments and clusters affect the growth of galaxies in greater
detail. One such mission is the European Space Agency's Herschel Space
Telescope, which has significant NASA involvement.

His paper on this topic has been accepted for publication in Astrophysical Journal
Letters. Co-authors on the paper include Andrea Biviano of the
INAF/Osservatorio Astronomico di Trieste, Italy; Florence Durret of Institut
d'Astrophysique de Paris, France; and Francine Marleau and Lisa Storrie-
Lombardi of the Spitzer Science Center, Pasadena, Calif.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space
Telescope mission for NASA's Science Mission Directorate, Washington. Science
operations are conducted at the Spitzer Science Center at the California Institute
of Technology, also in Pasadena. Caltech manages JPL for NASA.

For more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer

and http://www.nasa.gov/spitzer.

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