by Many small galaxies that existed early in the universe’s history have elongated into a surfboard-like shape, reflecting the influence of the Cosmic web of matter and ongoing mergers with other small galaxies, as revealed by deep telescope observations James Webb Space.
New research using the James Webb Space Telescope (JWST) has found that dwarf galaxies in the early universe often look flat, either ‘prolate’ (stretched along one axis) or very narrow ovals shaped like a surfboard, but others have more frisbee. like oblate appearance. These galactic frisbees seem to grow more abundant as the universe ages, as do the compact, spheroidal-shaped galaxies.
“About 50 to 80% of the galaxies we studied appear to be balanced in two dimensions,” Viraj Pandya, a Columbia University astronomer and lead author of a new paper describing the research, said in a press release. “[They] they appear to be very common in the early universe, which is surprising given their relative rarity.”
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Data were used from Cheers, or Cosmic Evolution Early Release Science, JWST’s program to push back the veil and explore the lives of the oldest and faintest galaxies in the universe. It is an era that lasted from 600 million years after the Big bang until 6 billion years later, during which the galaxies we see in the universe around us today developed, grew and matured, from grains such as the The Milky Way and the Andromeda Galaxyto giant ellipticals such as M87.
CEERS builds on work done by the Hubble Space Telescope, who studied the early universe in its deep-field images and in its CANDELS (Extragalactic Deep Legacy Near-Infrared Cosmic Assembly Cosmic Survey) program. Hubble discovered that giant galaxies in the early universe tended to be oblate spheroids, not unlike the elliptical galaxies of today. Smaller galaxies were harder for Hubble to detect, but from what it could see, many appeared elongated consisting of chains of brighter ‘blobs’, while other irregular dwarfs were known as ‘tamps’ which had an irregular shape, ‘knappini’ or ‘clumps’.
The question was, given Hubble’s limitations, could true reflections be seen in the shapes of smaller, smaller galaxies? The JWST’s larger vision has now confirmed Hubble’s earlier discoveries to be true.
Kartheik Iyer, also from Columbia University, described how JWST’s greater vision and sensitivity compared to Hubble is changing the study of galaxies in the early universe.
“It is exciting to identify additional categories for the early galaxies – there are many more to be analyzed now,” Iyer said in the press release. “We can now study how the shapes of galaxies relate to their appearance and how they formed their reflection in much greater detail.”
A picture now emerges of how galaxies can evolve and grow over time.
Matter is distributed throughout the universe primarily in a cosmic web of filaments that span the cosmos. These filaments are mostly made from dark dark, with a fraction of the normal matter mixed into the galaxies we observe. The abundance of prolate surfboard-shaped galaxies could be explained by their formation inside haloes of dark matter elongated in alignment with their cosmic web filament. Since other dwarf galaxies would also be forming within that filament, they would merge along it, resulting in the growth of elongated, chain-like galaxies.
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Over billions of years, the cosmic filaments spread and grow more diffuse. The merger rate slows and the fraction of prolate galaxies decreases as they begin to spin and assume an oblate disc-like structure. Such oblate galaxies are seen to increase from 20 to 60% over time and for a given galaxy mass.
Likewise, spheroidal galaxies grow more abundant over time, as dense star-forming galaxies settle in the universe to become the progenitors of the giant elliptical galaxies we see today, or the spheroidal bubbles of giant spiral galaxies.
A key objective of JWST is to understand the evolution of galaxies over cosmic history. The new CEERS results suggest that hierarchical merging—smaller galaxies merging with larger ones, along the aforementioned cosmic filaments—is key to understanding these different galaxy shapes.
The results appear in a paper to be published in a future issue of the Astrophysical Journal.
