ALMA and James Webb explore one of the most distant galaxies in the Universe

Astronomers used ALMA and the James Webb Observatory (JWST) to study one of the most distant galaxies in the Universe. It existed just 400 million years after the Big Bang.

Galaxy GHZ2. Source: J. Zavala et al.

Since its inception, the JWST telescope has discovered many galaxies located at the outskirts of the observable Universe. One of them is GHZ2, whose redshift is z=12.333, corresponding to a period about 400 million years after the Big Bang. This means that we observe it as it was when the age of the cosmos was only 3% of the current age. 

The study of the properties of such objects is extremely important for testing current theories of galaxy formation and evolution. However, detailed and sensitive astronomical observations, particularly spectroscopy, are needed to understand their internal physics. But such observations are very difficult for these galaxies, which is not surprising given the vast distance to them.

To accomplish this task, the researchers engaged a tandem of JWST and ALMA to observe GHZ2. They managed to record the emission of excited hydrogen and oxygen atoms. This is the first time they have been detected in galaxies more than 13 billion light-years away from us.

The team found that GHZ2 experiences extreme bursts of star formation under unique conditions. Its inferred metallicity (relative abundance of elements heavier than hydrogen) is much lower than that of most modern galaxies. However, this is expected given the age of the Universe at that time. In addition, GHZ2 has a young stellar population, which may partially explain its high luminosity due to the presence of short-lived, massive, and hot stars typically absent in more evolved galaxies.

Signal from ionized hydrogen detected in the spectrum of galaxy GHZ2. Source: J. Zavala et al.

The total mass of this galaxy is several hundred million times that of the sun. It is confined in a surprisingly small region of about 100 parsecs (326 light-years), indicating a high stellar density. Something similar is observed in globular clusters: massive, gravitationally bound associations of ancient stars. With this mysterious population of objects, GHZ2 has many features in common. These include low metallicity, chemical abundance anomalies, and high surface density star formation rates. Thus, objects like GHZ2 may help explain the origin of globular clusters, which has remained a mystery for many decades.

According to Almaobservatory.org

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