ALMA Spots Candidate for Most Distant Known Spiral Galaxy

ALMA Spots Candidate for Most Distant Known Spiral Galaxy

The star-forming disk galaxy with a two-armed spiral morphology, named BRI 1335-0417, existed when the Universe was just 1.4 billion years old.

ALMA detected the emission from carbon ions in the BRI 1335-0417 galaxy. Image credit: ALMA / ESO / NAOJ / NRAO / T. Tsukui & S. Iguchi, doi: 10.1126/science.abe9680.

BRI 1335-0417 was discovered in data from the Atacama Large Millimeter/submillimeter Array (ALMA).

“I was excited because I had never seen such clear evidence of a rotating disk, spiral structure, and centralized mass structure in a distant galaxy in any previous literature,” said lead author Takafumi Tsukui, a graduate student at SOKENDAI.

“The quality of the ALMA data was so good that I was able to see so much detail that I thought it was a nearby galaxy.”

Tsukui and his colleague, Professor Satoru Iguchi from SOKENDAI and the National Astronomical Observatory of Japan, found that BRI 1335-0417 has a two-armed spiral morphology that extends from about 6,500 to 16,300 light-years in radius.

“As BRI 1335-0417 is a very distant object, we might not be able to see the true edge of the galaxy in this observation. For a galaxy that existed in the early Universe, BRI 1335-0417 was giant,” Tsukui said.

The astronomers interpreted BRI 1335-0417’s features as due to a central compact structure, such as a bulge; a rotating gas disk; and either spiral arms or tidal tails.

They had formed within 1.4 billion years after the Big Bang, long before the peak of cosmic star formation.

“Then the question becomes, how was this distinct spiral structure formed in only 1.4 billion years after the Big Bang? We considered multiple possible causes and think that it could be due to an interaction with a small galaxy,” they said.

“BRI 1335-0417 is actively forming stars, and we found that the gas in the outer part of the galaxy is gravitationally unstable, which is conducive to star formation.”

“This situation is likely to occur when a large amount of gas is supplied from the outside, possibly due to collisions with smaller galaxies.”

“The fate of BRI 1335-0417 is also shrouded in mystery. Galaxies that contain large amounts of dust and actively produce stars in the ancient Universe are thought to be the ancestors of the giant elliptical galaxies in the present Universe.”

“In that case, BRI 1335-0417 changes its shape from a disk galaxy to an elliptical one in the future. Or, contrary to the conventional view, it may remain a spiral galaxy for a long time.”

The results were published in the journal Science.

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Takafumi Tsukui & Satoru Iguchi. Spiral morphology in an intensely star-forming disk galaxy more than 12 billion years ago. Science, published online May 20, 2021; doi: 10.1126/science.abe9680

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