Capturing the onset of galaxy rotation in the early universe
After the Big Bang came the earliest galaxies. Due to the expansion of the universe, these galaxies are receding away from us. This causes their emissions to be redshifted (shifted towards longer wavelengths). By studying these redshifts, it is possible to characterize the “motion” within the galaxies as well as their distance. In a new study, astronomers at Waseda University have now revealed a likely rotational motion of one such distant galaxy. Credit: Waseda University

Astronomers have been able to find more and more distant galaxies as telescopes have become more advanced. As the universe expanded, these are some of the earliest galaxies to form in it. The speed at which a galaxy moves away from us is related to the distance. It is possible to estimate how fast a galaxy is moving and when it was formed. The term "redshift" is used to describe the phenomenon of objects moving away from an observer and emitting light that appears to be shifted to the observer.

The ALMA telescope is located in the midst of the Atacama Desert and is well suited for observing redshifts. Professor Akio Inoue and graduate student Tsuyoshi Tokuoka are from Waseda University, Japan. Ellis says that studying the internal motion of gas and stars provides motivation for understanding the process of galaxy formation in the earliest possible universe. Their study has been published in a journal.

The formation of stars from the accumulated gas starts the formation of the galaxy. The star formation progresses from the center outward, a disk develops, and the galaxy is formed. Older stars stay in the central part while newer stars form in the rotating disk. It is possible to determine the stage of evolution of the galaxy by studying the age of the stars and gas.

The astronomer measured small differences in the "redshift" from position to position inside the galaxy and found that it was in line with the criteria for a rotation-dominated galaxy. They found that the observations were reproduced very well by the rotating disk model. The Milky Way disk has a rotation speed of 220 kilometers per second. The diameter of JD1 was measured at only 3000 light-years, much smaller than that of the Milky Way.

The earliest source yet found that has a rotating disk of gas and stars is by far the most distant of the three. The team has been able to see the gradual development of rotating galaxies over a large part of the history of our universe.

The mass estimated from the speed of the galaxy's rotation was in line with the mass previously estimated from the galaxy's signature, and came mostly from stars that formed about 300 million years ago. The stellar population inJD1 formed at an earlier time in the universe.

The rotation speed of JD1 is much slower than those found in other galaxies, and it is likely that it is at an initial stage of developing a rotation. Calculating the location of young and older stars in the universe is going to be easier thanks to the recently launched James Webb Telescope.

There are many new discoveries on the way.

More information: Possible Systematic Rotation in the Mature Stellar Population of a z = 9.1 Galaxy, The Astrophysical Journal Letters (2022). DOI: 10.3847/2041-8213/ac7447 Journal information: Astrophysical Journal Letters