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image at right shows a close-up of the colliding galaxies in red and
green. The red data show dust-enshrouded regions of star formation. The
green data show gas in the merging galaxies. The blue spots are
visible-light observations of galaxies located much closer to us.
Credit: JPL-Caltech/UC Irvine/Keck Observatory/STScI/NRAO/SAO/ESA/NASA.Hi-res image
Kamuela, Hawaii – Two hungry young galaxies that collided 11
billion years ago are rapidly forming a massive galaxy about 10 times
the size of the Milky Way, according to UC Irvine-led research conducted
on the W. M. Keck Observatory and other research facilities around the
world. The results will be published today in the journal Nature.
Capturing the creation of this type of large, short-lived star body
is extremely rare – the equivalent of discovering a missing link between
winged dinosaurs and early birds, said the scientists, who relied
primarily on data from Keck Observatory’s NIRC2 fitted with the laser
guide star adaptive optics (LGSAO) system. The new mega-galaxy, dubbed
HXMM01, is the brightest, most luminous and most gas-rich
submillimeter-bright galaxy merger known.
HXMM01 is fading away as fast as it forms, a victim of its own
cataclysmic birth. As the two parent galaxies smashed together, they
gobbled up huge amounts of hydrogen, emptying that corner of the
universe of the star-making gas.
“These galaxies entered a feeding frenzy that would quickly exhaust
the food supply in the following hundreds of million years and lead to
the new galaxy’s slow starvation for the rest of its life,” said lead
author Hai Fu, a UC Irvine postdoctoral scholar.
The discovery solves a riddle in understanding how giant elliptical
galaxies developed quickly in the early universe and why they stopped
producing stars soon after. Other astronomers have theorized that giant
black holes in the heart of the galaxies blew strong winds that expelled
the gas. But cosmologist Asantha Cooray, the UC Irvine team’s leader,
said that they and colleagues across the globe found definitive proof
that cosmic mergers and the resulting highly efficient consumption of
gas for stars are causing the quick burnout.
“Finding this type of galaxy is as important as the discovery of the
Archaeopteryx was in understanding dinosaurs’ evolution into birds,
because they were both caught at a critical transitional phase,” Fu
The new galaxy was initially spotted by UC Irvine postdoctoral
scholar Julie Wardlow, also with Cooray’s group. She noticed “an
amazing, bright blob” in images of the so-called cold cosmos – areas
where gas and dust come together to form stars – recorded by the
European Space Agency’s Herschel telescope with important contributions
from NASA’s Jet Propulsion Laboratory in Pasadena. “Herschel captured
carpets of galaxies, and this one really stood out.”
Follow-up views at a variety of wavelengths were obtained at more
than a dozen ground-based observatories, particularly the W.M. Keck
Observatory in Hawaii.
“The NIRC2/LGSAO image has revealed the existing stellar population
of this pair of galaxies,” Fu said. “The radiation captured by Keck
tells us how many stars have already been formed in the system at the
observed epoch. These data told us the constituents of the galaxy pair:
they are each made of half gas and half stars, which indicates they are
nascent galaxies in formation.
The NIRSPEC spectra measured the velocity difference of the two
galaxies at only 300 km/s, indicating that the two galaxies are soon to
merge instead of just flying by each other. The spectra also show the
high-velocity winds driven by the intense star formation in both
galaxies, uncovering the violent environment in these galaxies.
UC Irvine graduate student Jae Calanog is co-author of the paper, as
are scientists at 27 other institutions in the U.S., Canada, Spain,
France, England and South Africa. Funding was provided by NASA.
The W. M. Keck Observatory operates the largest, most scientifically
productive telescopes on Earth. The two 10-meter optical/infrared
telescopes on the summit of Mauna Kea on the Island of Hawaii feature a
suite of advanced instruments including imagers, multi-object
spectrographs, high-resolution spectrographs, integral-field
spectroscopy and a world-leading laser guide star adaptive optics
system. The Observatory is a private 501(c) 3 non-profit organization
and a scientific partnership of the California Institute of Technology,
the University of California and NASA. Visit keckobervatory.org for more information.