Unraveling the foundational structure of spiral galaxies, JWST delves into their formative processes
A groundbreaking study led by astronomers from the Australian National University, published in the Monthly Notices of the Royal Astronomical Society, has provided new insights into the origins and development of disk galaxies. Using the highly sensitive James Webb Space Telescope (JWST), the team analysed 111 edge-on galaxies, investigating the formation of their thick and thin disks for the first time at great cosmic distances.
The study's key findings reveal that disk galaxies typically form a thick stellar disk first, followed by the emergence of a thin stellar disk. This sequence has been observed as far back as 2.8 billion years after the Big Bang, or approximately 11 billion years ago.
Present-day disk galaxies, including the Milky Way, display a thick outer disk filled with older stars and an inner thinner disk harbouring younger stars. JWST's exceptional resolution and ability to see through dust allowed astronomers to distinguish these two components even in distant galaxies previously thought indistinguishable in this respect.
The timing of thin disk formation depends strongly on the galaxy’s mass. Larger, more massive galaxies began to develop thin disks around 8 billion years ago, while smaller galaxies started this process significantly later, around 4 billion years ago. This disparity is linked to the efficiency of star formation, with massive galaxies converting gas into stars faster, which stabilizes their disks sooner and allows thin disks to emerge earlier.
The observations support the "turbulent gas disk scenario" as a key mechanism behind disk formation. Early galaxies had chaotic, turbulent gas that collapsed rapidly, causing intense starbursts that created thick disks. As stars accumulated, they stabilized the gas, reducing turbulence and leading to the development of thinner, more orderly disks.
The study found that thick- and thin-disk formation are not isolated events. The thick disk continues to grow slowly even as the thin disk grows more rapidly. This ongoing growth suggests that the formation of disk galaxies is a continuous process, shaped by the turbulent early gas dynamics and the mass of the galaxy.
The timing of the transition from thick to thin disk formation observed in these distant galaxies roughly coincides with what is known about the Milky Way’s own disk development. JWST’s capability to observe smaller, fainter galaxies analogous to the Milky Way's progenitors promises to deepen our understanding of our galaxy’s history.
The research, with the DOI: 10.1093/mnras/staf604, was conducted using data pulled from JWST's data. The team was led by Takafumi Tsukui from the Australian National University. The study included galaxies that are as far as 3.8 billion years after the Big Bang.
This major advance refines our picture of how galaxies like the Milky Way formed their characteristic disk structures over cosmic time. The findings align with the turbulent gas disk scenario for thick- and thin-disk formation, providing compelling evidence for this theory. As we continue to explore the universe with JWST, we can expect more revelations about the formation and evolution of galaxies.
- The new insights from the study suggest that the field of environmental science, particularly the study of galaxy evolution, is closely related to spaces and astronomy, as it emphasizes the interplay between turbulent gas and the development of thin and thick stellar disks in galaxies over cosmic distances.
- The advancements in technology, such as the James Webb Space Telescope (JWST), have played a crucial role in the understanding of environmental science, enabling scientists to observe galaxy formation and evolution in greater detail, even unveiling the complexities in the emergence of thin disks in contrast to the thicker ones.
