Webb Sheds New Light on Structural Evolution of Disk Galaxies
Current disc galaxies often have distinct thin and thick discs. The training mechanisms of the two discs and the moment of their start are open questions. To answer these questions, astronomers have analyzed a statistical sample of 111 EDGE -On disc galaxies at various periods – up to 11 billion years ago, or around 2.8 billion years after the Big Bang – using archive data from the NASA / ESA / CSA James Webb space telescope.
Composite Images Web / Nircam of a quarter of the sample of the sorted team by increasing the red time. Image credit: tsukui and al., Doi: 10.1093 / minras / Staf604.
Current disc galaxies often contain a thick outdoor disc and filled with stars and an integrated thin disk.
For example, the thick disc of Milky Way has around 3,000 light years and its slim disc about 1,000 light years thick.
But how and why are these double-disc structures formed?
“Our unique measure of the thickness of the discs to a high red shift, or sometimes in the early universe, is a reference for the theoretical study which was only possible with Webb,” said Dr. Takafumi Tsukui, astronomer of the Australian National University.
“Usually, older thick disk stars are weak, and young thin discs surpass the whole galaxy.”
“But with the resolution of webb and the unique ability to see through dust and highlight small old stars, we can identify the structure with two discs of galaxies and measure their thickness separately.”
By analyzing 111 targets on board on cosmological time, astronomers were able to study unique disc galaxies and double -disc galaxies.
Their results indicate that the galaxies first form a thick disc, followed by a thin disc.
The moment when it takes place depends on the mass of the galaxy: galaxies with a single high mass disc went to two -billion years ago.
On the other hand, low -mass low -disc galaxies formed their thin discs integrated later, about 4 billion years ago.
“It is the first time that it is possible to resolve thin stellar discs with a higher red gap,” said Dr. Emily Wisnioski, also from the Australian National University.
“What is really new is to discover when thin stellar discs begin to emerge.”
“See thin stellar discs already in place 8 billion years ago, or even earlier, was surprising.”
To explain this transition from a unique and thick disc to a thick and thin disc, and the difference in synchronization for high and low mass galaxies, the researchers looked beyond their galaxy sample on the initial edge and examined the data showing the moving gas from the Atacamagame network with large millimeter / submimilimeter (Alma) and ground surveillance.
By taking into account the movement of galaxies gas discs, they found that their results aligned with the scenario of “turbulent gas disc” – one of the three major hypotheses that have been proposed to explain the process of forming thick and thin records.
In this scenario, a turbulent gas disc in the early universe causes training of intense stars, forming a thick stellar disc.
As the stars are formed, they stabilize the gas disc, which becomes less turbulent and, therefore, more thin.
Since massive galaxies can more effectively convert gas to star, they settled sooner than their low -mass counterparts, resulting in the previous formation of thin discs.
“Although this study structurally distinguishes thin and thick discs, there is still much more than we would like to explore,” said Dr. Tsukui.
“We want to add the type of information that people generally obtain for neighboring galaxies, such as stellar movement, age and metallicity.”
“In doing so, we can fill the ideas of galaxies near and far, and refine our understanding of the training of the disc.”
The results were published in the Monthly opinion from the Royal Astronomical Society.
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Takafumi Tsukui and al. 2025. The emergence of thin and thickened galactic discs through cosmic history. Mnra 540 (4): 3493-3522; DOI: 10.1093 / Mnras / Staf604
