[Spitzer News] Astronomers Eye Ultra-Young, Bright Galaxy in Early Universe

spitzer-news at lists.ipac.caltech.edu spitzer-news at lists.ipac.caltech.edu
Tue Feb 12 06:57:54 PST 2008

In this issue:

1) Astronomers Eye Ultra-Young, Bright Galaxy in Early Universe
2) Spitzer Catches Young Stars in Their Baby Blanket of Dust
3) Cosmic Suburbia is a Better Breeding Ground for Stars



NASA's Hubble and Spitzer space telescopes, with a boost from a  
natural "zoom lens," have uncovered what may be one of the youngest  
and brightest galaxies ever seen in the middle of the cosmic "dark  
ages," just 700 million years after the beginning of our universe.

The detailed images from Hubble's Near Infrared Camera and Multi- 
Object Spectrometer reveal an infant galaxy, dubbed A1689-zD1,  
undergoing a firestorm of star birth during the dark ages, a time  
shortly after the Big Bang but before the first stars reheated the  
cold, dark universe. Images from NASA's Spitzer Space Telescope's  
Infrared Array Camera provided strong additional evidence that it was  
a young star-forming galaxy in the dark ages.

"We certainly were surprised to find such a bright young galaxy 12.8  
billion years in the past," said astronomer Garth Illingworth of the  
University of California, Santa Cruz, and a member of the research  
team. "This is the most detailed look to date at an object so far back  
in time."

"The Hubble images yield insight into the galaxy's structure that we  
cannot get with any other telescope," added astronomer Rychard Bouwens  
of UC Santa Cruz, a co-discoverer. The new images should offer  
insights into the formative years of galaxy birth and evolution and  
yield information on the types of objects that may have contributed to  
ending the dark ages. The faraway galaxy also is an ideal target for  
Hubble's successor, the James Webb Space Telescope, scheduled to  
launch in 2013.

During its lifetime, the Hubble telescope has peered ever farther back  
in time, viewing galaxies at successively younger stages of evolution.  
These snapshots have helped astronomers create a scrapbook of galaxies  
from infancy to adulthood. The new Hubble and Spitzer images of A1689- 
zD1 show a time when galaxies were in their infancy.

Current theory holds that the dark ages began about 400,000 years  
after the Big Bang, as matter in the expanding universe cooled and  
formed clouds of cold hydrogen. These cold clouds pervaded the  
universe like a thick fog. At some point during this era, stars and  
galaxies started to form. Their collective light reheated the foggy,  
cold hydrogen, ending the dark ages about a billion years after the  
Big Bang.

"This galaxy presumably is one of the many galaxies that helped end  
the dark ages," said astronomer Larry Bradley of Johns Hopkins  
University in Baltimore, Md., and leader of the study. "Astronomers  
are fairly certain that high-energy objects such as quasars did not  
provide enough energy to end the dark ages of the universe. But many  
young star-forming galaxies may have produced enough energy to end it."

The galaxy is so far away it did not appear in images taken with  
Hubble's Advanced Camera for Surveys, because its light is stretched  
to invisible infrared wavelengths by the universe's expansion. It took  
Hubble's near infrared camera/spectrometer, Spitzer, and a trick of  
nature called gravitational lensing to see the faraway galaxy. The  
astronomers used a relatively nearby massive cluster of galaxies known  
as Abell 1689, roughly 2.2 billion light-years away, to magnify the  
light from the more distant galaxy directly behind it. This natural  
telescope is called a gravitational lens.

Though the diffuse light of the faraway object is nearly impossible to  
see, gravitational lensing has increased its brightness by nearly 10  
times, making it bright enough for Hubble and Spitzer to detect. A  
telltale sign of the lensing is the smearing of the images of galaxies  
behind Abell 1689 into arcs by the gravitational warping of space by  
the intervening galaxy cluster.

The images reveal bright, dense clumps of hundreds of millions of  
massive stars in a compact region about 2,000 light-years across,  
which is only a fraction of the width of our Milky Way Galaxy. This  
type of galaxy is not uncommon in the early universe, when the bulk of  
star formation was taking place, Bradley and Illingworth said.

Spitzer's images show the galaxy's mass is typical of galaxies in the  
early universe. Its mass is equivalent to several billions of sunlike  
stars, or just a tiny fraction of the mass of the Milky Way. "This  
observation confirms previous Hubble studies that star birth happens  
in very tiny regions compared with the size of the final galaxy,"  
Illingworth said.

Even with the increased magnification from the gravitational lens,  
Hubble's sharp "eye" can only see knots of the brightest, heftiest  
stars in the galaxy. The telescope cannot pinpoint fainter, lower-mass  
stars, individual stars, or the material surrounding the star-birthing  
region. To see those things, astronomers will need the infrared  
capabilities of the Webb Telescope. The planned infrared observatory  
will have a mirror about seven times the area of Hubble's primary  
mirror and will collect more light from faint galaxies. It also will  
be able to view even more remote galaxies whose light has been  
stretched deep into infrared wavelengths that are out of the reach of  

Team member Holland Ford of Johns Hopkins University said this galaxy  
will be one of the first objects the Webb Telescope will observe,  
saying, "This object is a pathfinder for the James Webb Space  
Telescope for deciphering what is happening in young galaxies." The  
astronomers noted that the faraway galaxy also would be an ideal  
target for the Atacama Large Millimeter Array, which, when completed  
in 2012, will be the world's most powerful radio telescope.

The results will appear in the Astrophysical Journal, with followup  
observations planned with Hawaii's Keck telescope.

The Space Telescope Science Institute conducts science operations for  
Hubble, a project of international cooperation between NASA and the  
European Space Agency. The institute is operated for NASA by the  
Association of Universities for Research in Astronomy, Inc.,  
Washington. The Jet Propulsion Laboratory, Pasadena, Calif., manages  
Spitzer for NASA's Science Mission Directorate. Science operations are  
conducted at the Spitzer Science Center at the California Institute of  
Technology, which manages JPL for NASA.




Newborn stars peek out from beneath their natal blanket of dust in  
this dynamic image of the Rho Ophiuchi dark cloud from NASA's Spitzer  
Space Telescope.

Called "Rho Oph" by astronomers, it's one of the closest star-forming  
regions to our own solar system. Located near the constellations  
Scorpius and Ophiuchus, the nebula is about 407 light years away from  

Rho Oph is made up of a large main cloud of molecular hydrogen, a key  
molecule allowing new stars to form out of cold cosmic gas, with two  
long streamers trailing off in different directions. Recent studies  
using the latest X-ray and infrared observations reveal more than 300  
young stellar objects within the large central cloud. Their median age  
is only 300,000 years, very young compared to some of the universe's  
oldest stars, which are more than 12 billion years old.

"Rho Oph is a favorite region for astronomers studying star formation.  
Because the stars are so young, we can observe them at a very early  
evolutionary stage, and because the Ophiuchus molecular cloud is  
relatively close, we can resolve more detail than in more distant  
clusters, like Orion," said Lori Allen, lead investigator of the new  
observations, from the Harvard-Smithsonian Center for Astrophysics,  
Cambridge, Mass.

This false-color image of Rho Oph's main cloud, Lynds 1688, was  
created with data from Spitzer's infrared array camera, which has the  
highest spatial resolution of Spitzer's three imaging instruments, and  
its multiband imaging photometer, best for detecting cooler materials.

The colors in this image reflect the relative temperatures and  
evolutionary states of the various stars. The youngest stars are  
surrounded by dusty disks of gas from which they and their potential  
planetary systems are forming. These young disk systems show up as red  
in this image. Some of these young stellar objects are surrounded by  
their own compact nebulae. More evolved stars, which have shed their  
natal material, are blue.

The extended white nebula in the center right of the image is a region  
of the cloud glowing in infrared light due to the heating of dust by  
bright young stars near the cloud's right edge. Fainter, multi-hued  
diffuse emission fills the image. The color of the nebulosity depends  
on the temperature, composition and size of the dust grains. Most of  
the stars forming now are concentrated in a filament of cold, dense  
gas that shows up as a dark cloud in the lower center and left side of  
the image against the bright background of the warm dust.

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.

Spitzer's infrared array camera was built by NASA's Goddard Space  
Flight Center, Greenbelt, Md. The instrument's principal investigator  
is Giovanni Fazio of the Harvard-Smithsonian Center for Astrophysics.  
The multiband imaging photometer for Spitzer was built by Ball  
Aerospace Corporation, Boulder, Colo.; the University of Arizona; and  
Boeing North American, Canoga Park, Calif. Its principal investigator  
is George Rieke of the University of Arizona, Tucson.




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

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  

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  

"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  

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.



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