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The earliest example of merging galaxies ever found

Galaxy fusions are not particularly rare, but they are important events. Not only for the galaxies involved, but also for scientists who try to summarize the formation of galaxies. Now astronomers using ALMA have found the earliest example of galactic fusion so far.

The pair of merging galaxies in question is B14-65666, a cumbersome but scientifically useful name. (At the moment we will call it an "object.") The object is located in the constellation "Sextane" at a distance of 13 billion light years. That is, the light we are seeing now left the object 13 billion years ago, shortly after the beginning of the universe.

This is not the first time this object has been discovered. The Hubble used to discover this object, but it appeared to the Hubble as two separate objects, probably star clusters. However, the team with the Atacama Large Millimeter / Submillimeter Array (ALMA), perhaps the most sensitive radio telescope in the world, showed 1

3 billion years ago that the object is actually two merging galaxies.

The results of these new observations are published in publications of the Astronomical Society of Japan dated June 18, 2019. The name of the publication is "Big Three Dragons": az = 7.15 Lyman Break Galaxy Detected in [OIII] 88 um, [CII] 158 um and Dust Continuum with ALMA. "Lead author of the study is Takuya Hashimoto of Waseda University, Japan.

When Hubble looked at the object, it was limited to the ultraviolet spectrum. With this restriction, the object appeared to be two star clusters, one in the northeast and one in the southwest. But when Hashimoto and his team used Alma's power to examine the object, they saw something else: the telltale fingerprints of chemical elements.

ALMA was able to detect the radio wave emissions of carbon, oxygen and dust in the object. The recognition of these three signals was the key to unlocking the nature of the object.

The analysis showed that the object actually has two parts, just like Hubble Saw. But the signals of carbon, oxygen and dust have added another layer of information about the object thanks to ALMA. It turned out that the two blobs are different but form a single system. Each blob moves at a different speed, showing that two galaxies are merging.

Artistic representation of the merging galaxies B14-65666 at 13 billion light-years distance. Credit: NAOJ.

"With the extensive data from ALMA and HST combined with advanced data analysis, we were able to show that B14-65666 is a pair of merging galaxies in the earliest era of the universe," explains Dr. Hashimoto in a press release. "The detection of radio waves from three components in such a distant object demonstrates ALMA's high ability to probe the distant universe."

According to the study, the object is today the earliest known example of galaxy fusion. The researchers also estimated the total stellar mass of B14-65666 to be less than 10% of the Milky Way's mass. This means that the object is at the earliest stage of its development. This makes sense because it is ancient.

Although the object is young, it is much more active in star production than our own galaxy. ALMA observations revealed high temperatures and brightness in the dust. The authors say that this is probably due to very strong ultraviolet radiation generated by active star formation. This active star formation is another indication of the fusion of galaxies, as colliding galaxies are subject to strong gas compression, which triggers star formation thrusts. As the authors in their paper say: "… we argue that B14-65666 is a main fusion-induced starburst galaxy."

This is a composite image of object B14-65666. Red is dust, oxygen is green and carbon is blue. White are stars as seen by the Hubble Space Telescope. Picture credits: ALMA (ESO / NAOJ / NRAO), NASA / ESA Hubble Space Telescope, Hashimoto et al.

Akio Inoue, a professor at Waseda University and a member of the research team. "Ultimately, we hope to observe the circulation and accumulation of elements and material associated with the formation and evolution of galaxies."

Galaxy fusions are an important part of the evolution of galaxies. Often a larger galaxy ingests a smaller galaxy. Small galaxies can join together to form larger galaxies, although this is considered rare. Our own Milky Way has experienced mergers that have helped it grow to its present enormous size.

In an article published in 2018, astronomers presented evidence based on a century of observations showing that the Milky Way contains a population of stars from another galaxy. About ten billion years ago, another galaxy collided with our own, leaving behind a significant population of stars in the inner galactic halo. The authors of this paper argued that these stars came from a small galaxy about the size of the small Magellanic cloud.

In about 4.5 billion years, the Milky Way will collide with the Andromeda galaxy and merge. The resulting galaxy may be called Milkdromeda. And right now the Milky Way merges with the much smaller ghost galaxy called Antlia 2 (Ant 2) or eats it.

The authors of the study believe that, as in our Milky Way, there may be more mergers in the objects of the future (past?) That have not yet been discovered. The article states, "Although our current data does not show any companion objects in the B14-65666 environment, future deeper ALMA data may uncover companion galaxies around B14-65666." They conclude that the object is a prime candidate for follow-up observations. "Given the abundant data available and the spatially expanded nature, B14-65666 is one of the best targets for follow-up observations with ALMA and James Webb Space Telescope …"


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