By studying how distant starburst galaxies are
clustered together, astronomers in early 2012 found that they
eventually become so-called giant elliptical galaxies -- the most
massive galaxies in today's universe. The galaxies are so distant that
their light has taken around ten billion years to reach us, so we see
them as they were about ten billion years ago.
"We know that massive elliptical galaxies stopped producing stars rather
suddenly a long time ago, and are now passive. And scientists are
wondering what could possibly be powerful enough to shut down an entire
galaxy's starburst," said Julie Wardlow (University of California at Irvine and Durham University, UK)
"This is the first time that we've been able to show this clear link between the most energetic starbursting galaxies in the early Universe,
and the most massive galaxies in the present day," explains Ryan Hickox
(Dartmouth College, USA and Durham University, UK), the lead scientist
of the team.
Because of this extreme distance, the infrared light from dust grains
heated by starlight is redshifted into longer wavelengths, and the
dusty galaxies are therefore best observed in submillimeter wavelengths
of light. The galaxies are thus known as submillimeter galaxies.
Astronomers have combined observations from the LABOCA camera on the ESO-operated 12-metreAtacama Pathfinder Experiment (APEX) telescope with measurements made with ESO's Very Large Telescope, NASA's Spitzer Space Telescope, and others, to look at the way that bright, distant galaxies are gathered together in groups or clusters.
The more closely the galaxies are clustered, the more massive are
their halos of dark matter — the invisible material that makes up the
vast majority of a galaxy's mass. The new results are the most accurate
clustering measurements ever made for this type of galaxy.
By measuring the masses of the dark matter halos around the galaxies,
and using computer simulations to study how these halos grow over time,
the astronomers found that these distant starburst galaxies from the
early cosmos eventually become giant elliptical galaxies — the most
massive galaxies in today's Universe.
Furthermore, the new observations indicate that the bright starbursts
in these distant galaxies last for a mere 100 million years — a very
short time in cosmological terms — yet in this brief time they are able
to double the quantity of stars in the galaxies. The sudden end to this
rapid growth is another episode in the history of galaxies that
astronomers do not yet fully understand.
The team's results provide a possible explanation for why massive
elliptical galaxies stopped producing stars rather a long time ago, and
are now passive.: at that stage in the history of the cosmos, the
starburst galaxies are clustered in a very similar way to quasars,
indicating that they are found in the same dark matter halos. Quasars
are among the most energetic objects in the Universe — galactic beacons
that emit intense radiation, powered by a supermassive black hole at
their center.
There is mounting evidence to suggest the intense starburst also
powers the quasar by feeding enormous quantities of material into the
black hole. The quasar in turn emits powerful bursts of energy that are
believed to blow away the galaxy's remaining gas — the raw material for
new stars — and this effectively shuts down the star formation phase.
"In short, the galaxies' glory days of intense star formation also
doom them by feeding the giant black hole at their center, which then
rapidly blows away or destroys the star-forming clouds," explains David
Alexander (Durham University, UK), a member of the team.
The 12-metre-diameter APEX telescope is located on the Chajnantor
plateau in the foothills of the Chilean Andes. APEX is a pathfinder for
ALMA, the Atacama Large Millimeter/submillimeter Array,
a revolutionary new telescope that ESO, together with its international
partners, is building and operating, also on the Chajnantor plateau.
APEX is itself based on a single prototype antenna constructed for
the ALMA project. The two telescopes are complementary: for example,
APEX can find many targets across wide areas of sky, which ALMA will be
able to study in great detail. APEX is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO.
Source: The Daily Galaxy via ESO
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