Capturing the start of the rotation of galaxies in the early Universe

As telescopes have become more sophisticated and powerful, astronomers are able to detect increasingly distant galaxies. These are some of the earliest galaxies to form in our universe and have begun to retreat from us as the universe expanded. In fact, the greater the distance, the faster a galaxy seems to be moving away from us. Interestingly, we can estimate how fast a galaxy moves, and in turn, when it formed based on how “red-shifted” its emission appears. This is similar to a phenomenon called the Doppler effect, where objects moving away from an observer emit the light that appears to be shifted to longer wavelengths (hence the term “redshift”) toward the observer.

Located in the center of Chile’s Atacama Desert, the Atacama Large Millimeter/submillimeter Array (ALMA) telescope is particularly suited to detecting such redshifts in galaxy emissions. Recently, a team of international researchers, including Professor Akio Inoue and graduate student Tsuyoshi Tokuoka from Waseda University, Japan; dr. Takuya Hashimoto at the University of Tsukuba, Japan; Professor Richard S. Ellis at University College London; and dr. Nicolas Laporte, a researcher at the University of Cambridge, UK, has observed red-shifted emissions from a distant galaxy, MACS1149-JD1 (hereinafter JD1), leading them to some interesting conclusions. “In addition to finding high redshifts, namely very distant galaxies, studying their internal motion of gas and stars provides the motivation to understand the process of galaxy formation in the earliest possible universe,” explains Ellis. The findings of their research have been published in The astrophysical diary letters†

The formation of galaxies begins with the accumulation of gas and continues with the formation of stars from that gas. Over time, star formation progresses from the center outwards, a galactic disk develops, and the galaxy takes on a particular shape. As star formation continues, new stars form in the rotating disk, while older stars remain in the central part. By studying the age of the stellar objects and the movement of the stars and gas in the galaxy, it is possible to determine the evolutionary stage of the galaxy.

By conducting a series of observations over a period of two months, the astronomers successfully measured small differences in the “redshift” from position to position within the galaxy and found that JD1 met the criterion for a galaxy dominated by rotation. . They then modeled the galaxy as a rotating disk and found that it reproduced the observations very well. The calculated rotational speed was about 50 kilometers per second, which was compared to the rotational speed of the Milky Way disk of 220 kilometers per second. The team also measured the diameter of JD1 at just 3,000 light-years, much smaller than the Milky Way’s diameter of 100,000 light-years.

The significance of their result is that JD1 is by far the most remote, and therefore the earliest source found to date containing a rotating disk of gas and stars. Together with similar measurements of nearby systems in the research literature, this has enabled the team to trace the gradual evolution of rotating galaxies over more than 95% of our cosmic history.

Furthermore, the mass is estimated on the basis of the rotation speed of the galaxy aligned with the stellar mass previously estimated from the galaxy’s spectral signature, and came primarily from that of “mature” stars formed about 300 million years ago. “This shows that the stellar population in JD1 formed in an even earlier epoch of the cosmic age,” Hashimoto said.

“The rotational speed of JD1 is much slower than in galaxies in later epochs and in our galaxy, and it is likely that JD1 is in an early stage of developing rotational motion,” says Inoue. With the recently launched James Webb Space Telescope, astronomers now plan to identify the locations of young and older stars in the galaxy to verify and update their galaxy formation scenario.

New discoveries are certainly on the horizon.