A study conducted by researchers who measured the relationship between the size and brightness of galaxies in the early universe, less than one billion years after the Big Bang. This information can provide insights into the evolution of galaxies and the processes that shaped them in their early stages of formation.
An international team of researchers including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) has studied the relation between galaxy size and luminosity of some of the earliest galaxies in the universe taken by the brand-new James Webb Space Telescope (JWST), less than a billion years after the Big Bang, reports a new study in The Astrophysical Journal Letters.
The result is part of the Grim Lens-Amplified Survey from Space (GLASS) Early-Release Science Program, led by University of California, Los Angeles, Professor Tommaso Treu. It is designed to examine the early universe when the first stars and galaxies formed, ionizing the surrounding neutral gas and allowing light to pass through. This is called the epoch of reionization.
However, the specifics of reionization are still unknown since up until now, telescopes have not been able to make detailed observations of galaxies during this time in the history of the universe.
Researchers would benefit from learning more about the reionization era if they could comprehend how stars and galaxies have developed to produce the universe we see today.
The original wavelength of light will shift to longer wavelength when it travels from the early universe to us. Thus, the rest-frame wavelength is used to clarify their intrinsic wavelength, rather than observed wavelength.Lilan Yang
One study, led by Kavli IPMU JSPS Fellow Lilan Yang, and including Project Researcher Xuheng Ding, used multiband NIRCAM imaging data from the GLASS-JWST program to measure galaxy size and luminosity to figure out the morphology and the size-luminosity relation from rest-frame optical to UV.
“It’s the first time that we can study the galaxy’s properties in rest-frame optical at redshift larger than 7 with JWST, and the size-luminosity is important for determining the shape of luminosity function which indicates the primary sources responsible for the cosmic reionization, i.e., numerous faint galaxies or relatively less bright galaxies.”
“The original wavelength of light will shift to longer wavelength when it travels from the early universe to us. Thus, the rest-frame wavelength is used to clarify their intrinsic wavelength, rather than observed wavelength.”
“Previously, with Hubble Space Telescope, we know the properties of galaxies only in rest-frame UV band. Now, with JWST, we can measure longer wavelength than UV,” said first author Yang.
At a redshift greater than 7, or around 800 million years after the Big Bang, the researchers discovered the first rest-frame optical size-luminosity connection of galaxies, enabling them to investigate the size as a function of wavelength. They discovered that the median size from rest-frame optical to UV was slightly smaller and ranged between 450 and 600 parsecs. But was this expected?
“The answer is we don’t know what’s to expect. Previous simulation studies give a range of predictions,” said Yang.
The scientists also discovered that when the slope was allowed to change, the size-luminosity connection had a somewhat steeper slope in the band with the shortest wavelength.
“That would suggest higher surface brightness density at shorter wavelength, hence less observational incompleteness correction when estimating luminosity function, but the result is not conclusive. We don’t want to over-interpret here,” said Yang.
The Astrophysical Journal Letters published the team’s paper on October 18, 2022.