Credit: NRAO/AUI/NSF
Animation zoom-in of the composite image of ADFS-27 galaxy
pair. The initial image is from ESA's Herschel Space Observatory. The
object was then detected by ESO's Atacama Pathfinder EXperiment (APEX)
telescope. ALMA (final zoom) was able to identify two galaxies: ADFS-27N
(for North) and ADFS-27S (for South). The starbursting galaxies are
about 12.8 billion light-years from Earth and destined to merge into a
single, massive galaxy. Credit: ESA/Herschel; ESO/APEX; ALMA (ESO/NAOJ/NRAO); D. Riechers et al. 2017
Pair of Exceptionally Rare Hyper-luminous Galaxies Discovered with ALMA
New observations with the Atacama Large Millimeter/submillimeter Array (ALMA)
have uncovered the never-before-seen close encounter between two
astoundingly bright and spectacularly massive galaxies in the early
universe. These so-called hyper-luminous starburst galaxies are
exceedingly rare at this epoch of cosmic history — near the time when
galaxies first formed — and may represent one of the most-extreme
examples of violent star formation ever observed.
Astronomers captured these two interacting galaxies, collectively
known as ADFS-27, as they began the gradual process of merging into a
single, massive elliptical galaxy. An earlier sideswiping encounter
between the two helped to trigger their astounding bursts of star
formation. Astronomers speculate that this merger may eventually form
the core of an entire galaxy cluster. Galaxy clusters are among the most
massive structures in the universe.
“Finding just one hyper-luminous starburst galaxy is remarkable in
itself. Finding two of these rare galaxies in such close proximity is
truly astounding,” said Dominik Riechers, an astronomer at Cornell
University in Ithaca, New York, and lead author on a paper appearing in
the Astrophysical Journal. “Considering their extreme distance
from Earth and the frenetic star-forming activity inside each, it’s
possible we may be witnessing the most intense galaxy merger known to
date.”
The ADFS-27 galaxy pair is located approximately 12.7 billion
light-years from Earth in the direction of the Dorado constellation. At
this distance, astronomers are viewing this system as it appeared when
the universe was only about one billion years old.
Astronomers first detected this system with the European Space
Agency’s Herschel Space Observatory. It appeared as a single red dot in
the telescope’s survey of the southern sky. These initial observations
suggested that the apparently faint object was in fact both extremely
bright and extremely distant. Follow-up observations with the Atacama
Pathfinder EXperiment (APEX) telescope confirmed these initial
interpretations and paved the way for the more detailed ALMA
observations.
With its higher resolution and greater sensitivity, ALMA precisely
measured the distance to this object and revealed that it was in fact
two distinct galaxies. The pairing of otherwise phenomenally rare
galaxies suggests that they reside within a particularly dense region of
the universe at that period in its history, the astronomers said.
The new ALMA observations also indicate that the ADFS-27 system has
approximately 50 times the amount of star-forming gas as the Milky Way.
“Much of this gas will be converted into new stars very quickly,” said
Riechers. “Our current observations indicate that these two galaxies are
indeed producing stars at a breakneck pace, about one thousand times
faster than our home galaxy.”
The galaxies — which would appear as flat, rotating disks — are
brimming with extremely bright and massive blue stars. Most of this
intense starlight, however, never makes it out of the galaxies
themselves; there is simply too much obscuring interstellar dust in
each.
This dust absorbs the brilliant starlight, heating up until it glows
brightly in infrared light. As this light travels the vast cosmic
distances to Earth, the ongoing expansion of the universe shifts the
once infrared light into longer millimeter and submillimeter
wavelengths, all thanks to the Doppler efecct.
Doppler effect,
ALMA was specially designed to detect and study light of this nature,
which enabled the astronomers to resolve the source of the light into
two distinct objects. The observations also show the basic structures of
the galaxies, revealing tail-like features that were spun-off during
their initial encounter.
The new observations also indicate that the two galaxies are about
30,000 light-years apart, moving at roughly several hundred kilometers
per second relative to each other. As they continue to interact
gravitationally, each galaxy will eventually slow and fall toward the
other, likely leading to several more close encounters before merging
into one massive, elliptical galaxy. The astronomers expect this process
to take a few hundred million years.
“Due to their great distance and dustiness, these galaxies remain
completely undetected at visible wavelengths,” noted Riechers.
“Eventually, we hope to combine the exquisite ALMA data with future
infrared observations with NASA’s James Webb Space Telescope. These two
telescopes will form an astronomer’s ‘dream team’ to better understand
the nature of this and other such exceptionally rare, extreme systems.”
The National Radio Astronomy Observatory is a facility of the
National Science Foundation, operated under cooperative agreement by
Associated Universities, Inc.
This research is presented in a paper titled “Rise of the titans: a
dusty, hyper-luminous ‘870 µm riser’ galaxy at z~6,” by D. Riechers, et
al., appearing in the Astrophysical Journal
. [http://iopscience.iop.org/article/10.3847/1538-4357/aa8ccf ].
The Atacama Large Millimeter/submillimeter Array (ALMA), an
international astronomy facility, is a partnership of ESO, the U.S.
National Science Foundation (NSF) and the National Institutes of Natural
Sciences (NINS) of Japan in cooperation with the Republic of Chile.
ALMA is funded by ESO on behalf of its Member States, by NSF in
cooperation with the National Research Council of Canada (NRC) and the
National Science Council of Taiwan (NSC) and by NINS in cooperation with
the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space
Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its
Member States; by the National Radio Astronomy Observatory (NRAO),
managed by Associated Universities, Inc. (AUI), on behalf of North
America; and by the National Astronomical Observatory of Japan (NAOJ) on
behalf of East Asia. The Joint ALMA Observatory (JAO) provides the
unified leadership and management of the construction, commissioning and
operation of ALMA.
