Three Primordial Galaxies Found Merging Near ‘Cosmic Dawn’
November 21, 2013

Three Primordial Galaxies Found Merging Near ‘Cosmic Dawn’

Lee Rannals for - Your Universe Online

Astronomers have found a group of primitive galaxies 13 billion light-years away sitting inside a blob of gas.

A team using the Atacama Large Millimeter/submillimeter Array (ALMA) telescope and NASA’s Hubble Space Telescope discovered three infant galaxies merging inside a giant bubble of hot ionized gas. The object, known as Himiko, is 10 times larger than typical galaxies discovered from this era and is comparable in size to our own galaxy.

“This exceedingly rare triple system, seen when the Universe was only 800 million years old, provides important insights into the earliest stages of galaxy formation during a period known as ‘Cosmic Dawn,’ when the Universe was first bathed in starlight,” Richard Ellis, the Steele Professor of Astronomy at the California Institute of Technology and member of the research team, said in a statement. “Even more interesting, these galaxies appear poised to merge into a single massive galaxy, which could eventually evolve into something akin to the Milky Way.”

Previous observations using the Spitzer Space Telescope suggested that Himiko was a single galaxy, but the latest study shows three distinct sources of light whose intense star formation is heating and ionizing a giant cloud of gas, said Masami Ouchi, an associate professor at the University of Tokyo.

Astronomers, publishing a paper in The Astrophysical Journal, noted that star formation regions like this should be filled with heavy elements like carbon, silicon, and oxygen. These elements come together to help create short-lived stars like those the Hubble detected. At the end of these massive stars’ lives, they explode to become supernovae, which helps scatter seeds of heavy elements across the intergalactic medium.

“When this dust is heated by ultraviolet radiation from massive newborn stars, the dust then re-radiates at radio wavelengths,” Kotaro Kohno, a member of the team also with the University of Tokyo, said in a statement. “Such radiation is not detected in Himiko.”

Ouchi said observations with ALMA revealed a complete absence of the signal from carbon, which is rapidly synthesized with young stars.

“Given the sensitivity of ALMA, this is truly remarkable. Exactly how this intense activity can be reconciled with the primitive chemical composition of Himiko is quite puzzling,” Ouchi said.

The astronomers believe that a large fraction of the gas in Himiko could have been created in the Big Bang. If this proves to be correct, it would be a landmark discovery signaling the detection of a primordial galaxy seen during its formation.

“Astronomers are usually excited when a signal from an object is detected. But, in this case, it’s the absence of a signal from heavy elements that is the most exciting result,” Ellis said.