Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered a pair of astoundingly bright and spectacularly massive galaxies in the early Universe. These so-called hyper-luminous starburst galaxies are approximately 12.8 billion light-years from Earth and destined to merge into a single, massive elliptical galaxy. A paper reporting this discovery is published in the Astrophysical Journal.
Artist’s impression of two starburst (star-forming) galaxies beginning to merge in the early Universe. Image credit: NRAO / AUI / NSF.
“Finding just one hyper-luminous starburst galaxy is remarkable in itself,” said Cornell University astronomer Dominik Riechers, lead author of the paper.
“Finding two of these rare galaxies in such close proximity is truly astounding.”
“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.”
Dr. Riechers and co-authors first detected these two galaxies, collectively known as ADFS-27, with ESA’s Herschel Space Observatory. The duo appeared as a single red dot in the telescope’s survey of the southern sky.
The initial observations suggested that the apparently faint object was in fact both extremely bright and extremely distant.
Follow-up observations with ESO’s Atacama Pathfinder Experiment telescope confirmed these initial interpretations and paved the way for the more detailed ALMA observations.
This composite image shows the ADFS-27 galaxy pair, which is located approximately 12.7 billion light-years from Earth in the direction of the Dorado constellation: the background image is from ESA’s Herschel Space Observatory; the object was then detected by ESO’s Atacama Pathfinder EXperiment telescope (middle image); ALMA (right) was able to identify two galaxies: ADFS-27N (for North) and ADFS-27S (for South). 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. Image credit: NRAO / AUI / NSF / B. Saxton / ESA Herschel / ESO APEX / ALMA / ESO / NAOJ / D. Riechers.
With its higher resolution and greater sensitivity, ALMA precisely measured the distance to the object and revealed that it was in fact two distinct galaxies.
The ALMA data also indicate that ADFS-27 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,” Dr. Riechers said.
“Our current observations indicate that these two galaxies are indeed producing stars at a breakneck pace, about 1,000 times faster than our own Galaxy.”
The ALMA observations also indicate that the two galaxies are 30,000 light-years apart, moving at roughly several hundred miles 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 elliptical galaxy.
The team expects this process to take a few hundred million years and speculate that the merger may eventually form the core of an entire galaxy cluster.
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Dominik A. Riechers et al. 2017. Rise of the Titans: A Dusty, Hyper-luminous ‘870 μm Riser’ Galaxy at z ~ 6. ApJ 850, 1; doi: 10.3847/1538-4357/aa8ccf
