Astronomers discover the most distant rotating galaxy

Due to the expansion of the universe, the primordial galaxies are moving further and further away from us. Their electromagnetic emissions are thus gradually shifted towards the red (because the wavelengths are stretched). By analyzing these redshifts, called “redshifts,” astronomers can determine how far away a galaxy is and how fast it is moving.

A rotating galaxy in the early universe

Thanks to increasingly powerful telescopes – such as ALMA in Chile – scientists can discover galaxies further and further away. The galaxy discussed here is located about 13.28 billion light years from Earth. Named MACS1149-JD1 (hereafter referred to as JD1), it is one of the first galaxies to form at the beginning of our universe.

Galaxies are formed by the accretion of gas and cosmic dust; from this nebula the stars are born. Over time, star production from the center of the gaseous cloud migrates outward, gradually forming a galactic disc. New stars then form in the rotating disc, while older stars remain in the central part. Thus, by studying the age and movement of stars and gas in the galaxy, it is possible to determine at what stage of its development the latter is.

This image shows the galaxy cluster MACS J1149.5+2223 taken with the Hubble Space Telescope; the inset image is the very distant galaxy MACS1149-JD1, seen as it was 13.3 billion years ago and observed with ALMA. Credit: ALMA (ESO/NAOJ/NRAO), NASA/ESA Hubble Space Telescope, W. Zheng (JHU), M. Postman (STScI), the CLASH team, Hashimoto et al.

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Thanks to the observational data collected over two months, the astronomers noticed small differences in the “redshift” (estimated at 9.1) from one point to another in the JD1 galaxy. These differences suggested that this galaxy met the criteria for a rotation-dominated galaxy. Computer modeling confirmed their hypothesis: the galaxy modeled as a rotating disc reproduced the observations very well.

A galaxy much slower than the Milky Way

The team reports a rotation speed of about 50 kilometers per second; its diameter has been estimated at “only” 3000 light years. By comparison, our Milky Way rotates on itself at 220 km/s, with a diameter of 100,000 light years. But what sets JD1 apart is that it is the most distant source (therefore the earliest) with a rotating stellar disk.

In addition to the discovery of galaxies with a high redshift, that is, very distant, the study of their internal motion of gas and stars makes it possible to understand the process of formation of galaxies in the earliest possible universe “Explains Richard Ellis, professor at University College London and co-author of the article reporting the discovery.

(left) Distribution of radio emission in MACS1149-JD1 observed by ALMA. The color shows the gas movement (in km/s) in the area where the speed measurements were made. The red color indicates that the gas is moving away from us, while the blue color indicates that it is approaching. The graduation from red to blue suggests the possibility that the gas is spinning disc-like around the center of the galaxy. (right) The model best suited to reproduce the observed motion of the gas. Credit: Tokuoka et al., ApJL (2022)

This discovery, combined with similar measurements of denser systems reported in the literature, allowed Ellis and his collaborators to describe the slow evolution of rotating galaxies through more than 95% of cosmic history.

The beginning of a rotational movement

The team found that the mass estimated from the galaxy’s rotation rate was consistent with the stellar mass previously estimated from its spectral signature. This mass corresponds mainly to a mature stellar population, formed during the first major star formation episode at z ≈ 15.” This shows that the stellar population of JD1 was formed at an even earlier time in the cosmic era. explains Dr. Takuya Hashimoto, from the University of Tsukuba.

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As the data show, the rotation rate of JD1 is much slower than that of galaxies from later epochs, such as ours. Because of this, the researchers believe that it is likely that JD1 is only at the beginning of its rotational motion.

The team now plans to track the location of young and old stars in this galaxy to verify – or, if necessary, update – their galaxy formation scenario. To do this, they will use the James Webb Space Telescope as soon as possible – which will officially begin its observing campaigns in a few days. This high-performance machine will undoubtedly allow them to rapidly advance their research.

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