Astronomers have discovered the most distant galaxy rotation ever observed, implying an early stage of rotational motion development.
The galaxies appeared first after the Big Bang. These galaxies are receding away from us as the universe expands. As a result, their emissions are redshifted (shifted towards longer wavelengths).
It is possible to characterize the “motion” within galaxies as well as their distance by analyzing these redshifts. Waseda University astronomers have discovered a likely rotational motion of one such distant galaxy in the new research.
Astronomers have been able to identify more and more distant galaxies as telescopes have become more sophisticated and strong. These are some of the first galaxies to form in our universe, and as the universe expanded, they began to recede from us. In reality, the greater the distance between the galaxies, the faster it tends to move away from us.
Researchers can estimate how fast a galaxy is moving, and thus when it formed, by observing how “redshifted” its emission appears. This is comparable to the “Doppler effect,” in which moving objects emit light that seems to be moved towards longer wavelengths (hence the term “redshift”) to the observer.
The Atacama Large Millimeter/submillimeter Array (ALMA) telescope, situated in Chile’s Atacama Desert, is especially well-suited for noticing such redshifts in galaxy emissions.
Recently, a team of international researchers has witnessed redshifted emissions of a distant galaxy, MACS1149-JD1 (hereafter JD1), which has directed them to some fascinating conclusions.
The team of researchers includes Professor Akio Inoue and graduate student Tsuyoshi Tokuoka from Waseda University, Japan, Dr. Takuya Hashimoto at the University of Tsukuba, Japan, and Professor Richard S. Ellis at University College London, and Dr. Nicolas Laporte, a research fellow at the University of Cambridge, UK.
Beyond finding high-redshift, namely very distant, galaxies, studying their internal motion of gas and stars motivates understanding the process of galaxy formation in the earliest possible universe.
Richard S. Ellis, Professor, University College London
The findings of their study have been published in The Astrophysical Journal Letters.
The formation of a galaxy starts with the buildup of gas and continues with the formation of stars from that gas. Star formation advances from the center outward, forming a galactic disc and giving the galaxy its distinctive shape.
Newer stars form in the rotating disc as star formation continues, while older stars remain in the center. The phase of the evolution of the galaxy can be investigated by analyzing the age of stellar objects and the motion of stars and gas in the galaxy.
Over two months, the astronomers successfully measured small differences in the “redshift” from position to position within the galaxy and discovered that JD1 met the criterion for a galaxy dominated by rotation.
They then modeled the galaxy as a rotating disc and discovered that it accurately reproduced the observations. The calculated rotational speed was around 50 kilometers per second, compared to the Milky Way disk’s rotational speed of 220 kilometers per second. The group also evaluated JD1’s diameter at 3,000 light-years, which is much narrower than the Milky Way’s diameter of 100,000 light-years.
The importance of their discovery is that JD1 is by far the most faraway and thus earliest source found to date that has a rotating disk of gas and stars. Together with measurements from nearby systems in the scientific literature, the group was able to trace the gradual evolution of rotating galaxies over more than 95% of our cosmic history.
Moreover, the mass approximated from the galaxy’s rotational speed was consistent with the stellar mass previously estimated from the galaxy’s spectral signature and was primarily derived from “mature” stars that formed around 300 million years ago.
“This shows that the stellar population in JD1 formed at an even earlier epoch of the cosmic age,” says Hashimoto.
“The rotation speed of JD1 is much slower than those found in galaxies in later epochs and our Galaxy and it is likely that JD1 is at an initial stage of developing a rotational motion,” says Inoue.
Astronomers intend to use the newly launched James Webb Space Telescope to find the location of young and older stars in the galaxy to confirm and upgrade their circumstances of galaxy formation.
Tokuoka, T., et al. (2022) Possible Systematic Rotation in the Mature Stellar Population of a z = 9.1 Galaxy. The Astrophysical Journal Letters. doi.org/10.3847/2041-8213/ac7447.