The James Webb Space Telescope and ALMA’s most powerful group capture the heart of the most distant galaxy cluster


University of Tsukuba

The study of how individual stars are born and die in galaxies, how new stars are born from the remains of old stars, and how galaxies evolve are important topics in astronomy. literature, because they give insight into our origins in the Universe. Galaxy clusters, some of the largest structures in the Universe, are collections of more than 100 galaxies held together by mutual gravity. Observations of nearby galaxies have shown that the growth of a galaxy depends on its environment in the sense that mature stellar populations are often observed in areas of galaxy density dense. This is called the “environmental effect”. Although environmental effects are considered an important factor in understanding the formation and evolution of galaxies, it is unclear when in the history of the Universe this effect began. One of the keys to understanding this is to observe the ancestors of galaxy clusters shortly after the birth of the Universe; Called the proto-galaxy cluster (hereinafter the proto-cluster), this is a collection of about 10 distant galaxies. Fortunately, astronomy allows us to observe the distant Universe as before. For example, light from a galaxy 13 billion light years away takes 13 billion years to reach Earth. So what we observe now is what this galaxy looked like 13 billion years ago. However, light traveling 13 billion light years becomes fainter, so telescopes observing it must have high sensitivity and spatial resolution.

An international research team led by Assistant Professor Takuya Hashimoto (University of Tsukuba, Japan) and researcher Javier Álvarez-Márquez (Spanish Center for Astrobiology) used the Space Telescope James Webb (JWST, visible light and infrared observations) and the Atacama Large Millimeter. /submillimeter Array (ALMA, radio observation) to study the “heartland” of the A2744z7p9OD protocol. Protozoal cluster A2744z7p9OD has been announced as the most distant protocluster at a distance of 13.14 billion light years[1] based on observations with JWST by another research group .“However, we were not able to observe the entire central, metropolitan region, which has the largest number of candidate galaxies in this protocol. It is unclear whether the environmental impact of galaxies begins in this protocol. So we decided to focus our research on the Central region,” Hashimoto said.

The research team first observed the central region of this protocol using JWST. Using NIRSpec, a spectroscopic observatory at wavelengths from the visible to the near-infrared, the team performed integral field spectroscopic observations that can simultaneously obtain spectra from all positions in the field of view. The team successfully detected ionized light from oxygen ions ([OIII] 5008 Å) coming from four galaxies in a quadrangle measuring 36,000 light-years along one edge, equivalent to half a semi-quadrangle. glass of the Milky Way (Figure 2 left). . Based on the redshift of this light (the stretching of wavelengths due to the expansion of the universe), the distance between the four galaxies and Earth has been determined to be 13.14 billion light years.

Yuma SUGAhara (Waseda/NAOJ), head of the research team, explains: “I was surprised that we identified four galaxies by detecting oxygen ion emission at approximately the same distance. The ‘candidate galaxies’ in the central region are actually members of the most distant protocluster.” JWST data analysis. In addition, the research team also paid attention to the archival data ALMA collected for this area. The data records radio emissions from cosmic dust in these distant galaxies. After analysis, they detected dust coming from three of the four galaxies (Figure 2, right). This is the first detection of dust emissions in member galaxies of a protocluster this distant in time. Cosmic dust in galaxies is thought to be supplied by supernova explosions at the end of the evolution of massive stars in galaxies, providing the material needed for the formation of new stars. . Therefore, the presence of large amounts of dust in a galaxy indicates that many of the galaxy’s first generation stars have completed their lives and that the galaxy is evolving.

Professor Luis Colina (El Centro de Astrobiología (CAB, CSIC-INTA)) describes the significance of the results: “No cosmic dust emission was detected in member galaxies of the protocluster outside the central area. The results indicate that many galaxies were concentrated into a small area and that galaxy growth accelerated, suggesting that environmental effects did not persist until about 700 million years after the Big Bang.

In addition, the research team conducted galaxy formation simulations to theoretically test the formation and evolution of four galaxies in the central region. The results show that a region of dense gas particles existed about 680 million years after the Big Bang, as shown in Figure 3(a). Figure 3(b) zooms in on Figure 3(a) and shows four galaxies forming, similar to the observed central region. To track the evolution of these four galaxies, the simulation calculated physical processes such as stellar and gas dynamics, chemical reactions, star formation, and supernovae. Simulations show that four galaxies merged and evolved into a larger galaxy within a few tens of millions of years, representing a short time scale in the evolution of the Universe. “We managed to reproduce the properties of galaxies in the central region thanks to the high spatial resolution of our simulations and the large number of galaxy samples we had. In the future, we want to explore the formation mechanism of the central region and its dynamic properties in more detail,” said Yurina Nakazato, a PhD student at the University of Tokyo who analyzed the data. simulation, said.

Javier Álvarez-Márquez (Spanish Center for Astrobiology) said: “We will make more sensitive observations of the protocluster A2744z7p9OD with ALMA to see if there are any galaxies that cannot be seen with previous sensitivity or not. We will also apply the JWST and ALMA observations, which have proven to be very powerful, to more protoclusters to elucidate the mechanism of galaxy evolution and explore our origins in the Universe. »