Herschel Measures Dark Matter Required for Star-Forming Galaxies

"If you start with too little dark matter, then a developing galaxy
would peter out," said astronomer Asantha Cooray of the University of
California, Irvine. He is the principal investigator of new research
appearing in the journal Nature, online on Feb. 16 and in the Feb. 24
print edition. "If you have too much, then gas doesn't cool
efficiently to form one large galaxy, and you end up with lots of
smaller galaxies. But if you have the just the right amount of dark
matter, then a galaxy bursting with stars will pop out."

This right of amount of dark matter turns out to be a mass equivalent
to 300 billion of our suns.

Herschel launched into space in May 2009. The mission's large,
3.5-meter telescope detects longer-wavelength infrared light from a
host of objects, ranging from asteroids and planets in our own solar
system to faraway galaxies.

"This remarkable discovery shows that early galaxies go through
periods of star formation much more vigorous than in our present-day
Milky Way," said William Danchi, Herschel program scientist at NASA
Headquarters in Washington. "It showcases the importance of infrared
astronomy, enabling us to peer behind veils of interstellar dust to
see stars in their infancy."

Cooray and colleagues used the telescope to measure infrared light
from massive, star-forming galaxies located 10 to 11 billion
light-years away. Astronomers think these and other galaxies formed
inside clumps of dark matter, similar to chicks incubating in eggs.

Giant clumps of dark matter act like gravitational wells that collect
the gas and dust needed for making galaxies. When a mixture of gas
and dust falls into a well, it condenses and cools, allowing new
stars to form. Eventually enough stars form, and a galaxy is born.

Herschel was able to uncover more about how this galaxy-making process
works by mapping the infrared light from collections of very distant,
massive star-forming galaxies. This pattern of light, called the
cosmic infrared background, is like a web that spreads across the
sky. Because Herschel can survey large areas quickly with high
resolution, it was able to create the first detailed maps of the
cosmic infrared background.

"It turns out that it's much more effective to look at these patterns
rather than the individual galaxies," said Jamie Bock of NASA's Jet
Propulsion Laboratory in Pasadena, Calif. Bock is the U.S. principal
investigator for Herschel's Spectral and Photometric Imaging Receiver
instrument used to make the maps. "This is like looking at a picture
in a magazine from a reading distance. You don't notice the
individual dots, but you see the big picture. Herschel gives us the
big picture of these distant galaxies, showing the influence of dark matter."

The maps showed the galaxies are more clustered into groups than
previously believed. The amount of galaxy clustering depends on the
amount of dark matter. After a series of complicated numerical
simulations, the astronomers were able to determine exactly how much
dark matter is needed to form a single star-forming galaxy.

"This measurement is important, because we are homing in on the very
basic ingredients in galaxy formation," said Alexandre Amblard, also
of UC Irvine, first author of the Nature paper. "In this case, the
ingredient, dark matter, happens to be an exotic substance that we
still have much to learn about."

NASA's Herschel Project Office is based at JPL, which contributed
mission-enabling technology for two of Herschel's three science
instruments. The NASA Herschel Science Center, part of the Infrared
Processing and Analysis Center at the California Institute of
Technology in Pasadena, supports the U.S. astronomical community.

For more information about Herschel, visit:

http://www.nasa.gov/herschel

http://www.esa.int/herschel

Source: NASA

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