Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have observed a disk bending wave in BRI 1335-0417, the oldest known spiral galaxy at over 12 billion years old. This unprecedented observation reveals the galaxy’s dynamic growth patterns, showcasing a vertically oscillating disk movement similar to ripples on a pond. The study marks the first time such phenomena have been detected in an early galaxy.
This simulation illustrates a galaxy disk being disturbed, leading to the propagation of a seismic ripple throughout the disk. Image credit: Bland-Hawthorn & Tepper-Garcia, University of Sydney.
Bar structure plays a crucial role in driving galaxy evolution and shaping disk structure.
In galaxies an axisymmetric stellar bar exerts gravitational torque on the gas, driving it towards the galactic center and forming a centralized stellar structure such as a bulge and nuclear disk.
This process may also promote gas accretion onto the black hole observed as active galactic nuclei.
Bars can also drive radial migration of gas and stars, which is essential for explaining the observed stellar kinematics in Milky Way-like galaxies.
“A state-of-the-art telescope called ALMA allowed them to look at the ancient galaxy BRI 1335-0417 in much greater detail,” said lead author Dr. Takafumi Tsukui, an astronomer at Australian National University.
“Specifically, we were interested in how gas was moving into and throughout the galaxy.”
“Gas is a key ingredient for forming stars and can give us important clues about how a galaxy is actually fuelling its star formation.”
In this case, Dr. Tsukui and colleagues were able to not only capture the motion of the gas around BRI 1335-0417, but also reveal a seismic wave forming — a first in this type of early galaxy.
The galaxy’s disk moves in a way not dissimilar to ripples spreading on a pond after a stone is thrown in.
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.
“The vertically oscillating motion of the disk is due to an external source, either from new gas streaming into the galaxy or by coming into contact with other smaller galaxies,” Dr. Tsukui said.
“Both possibilities would bombard the galaxy with new fuel for star formation.”
“Additionally, our study revealed a bar-like structure in the disk.”
“Galactic bars can disrupt gas and transport it towards the galaxy’s center.”
“The bar discovered in BRI 1335-0417 is the most distant known structure of this kind.”
“Together, these results show the dynamic growth of a young galaxy.”
“Early galaxies have been found to form stars at a much faster rate than modern galaxies,” said co-author Dr. Emily Wisnioski, also from Australian National University.
“This is true for BRI 1335-0417, which, despite having a similar mass to our Milky Way, forms stars at rate a few hundred times faster.”
“We wanted to understand how gas is supplied to keep up with this rapid rate of star formation.”
“Spiral structures are rare in the early Universe, and exactly how they form also remains unknown.”
“This study also gives us crucial information on the most likely scenarios.”
“While it is impossible to observe the galaxy’s evolution directly, as our observations only give us a snapshot, computer simulations can help piece the story together.”
The findings appear in the Monthly Notices of the Royal Astronomical Society.
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Takafumi Tsukui et al. 2024. Detecting a disc bending wave in a barred-spiral galaxy at redshift 4.4. MNRAS 527 (3): 8941-8949; doi: 10.1093/mnras/stad3588
