Webb reveals metal-rich galaxies in the early universe

The Webb telescope has revealed a galaxy in the distant universe that surprisingly seems to have hosted several generations of stars, although its age is estimated at 1.4 billion years.

This galaxy is the previously hidden companion in the light of another foreground galaxy, SPT0418-47, one of the brightest star-forming dusty galaxies in the early universe, whose distant light is bent and stretched by the gravity of a foreground galaxy. forming a circle, called an Einstein ring. “We found that this galaxy is chemically super-abundant, something none of us expected,” said Bo Peng, a Cornell University astronomy doctoral student who led the data analysis as lead author of a published study. in Astrophysical Journal Letters.

By investigating the spectral data embedded in each pixel of the images from JWST’s NIRSpec instrument, Peng identified a second new light source inside Einstein’s ring. He determined that the two new sources were images of a new galaxy that was being gravitationally lensed by the same foreground galaxy responsible for the ring’s creation, although they were eight to 16 times fainter, a testament to the power of vision. JWST Infrared.

Further analysis of the chemical composition of the light confirmed that the strong emission lines from hydrogen, nitrogen, and sulfur atoms exhibited similar redshifts, a measure of how much light from a galaxy is stretched toward longer wavelengths. and red as it moves away. This put the two galaxies at roughly the same distance from Earth—calculated as a redshift of about 4.2, or about 10% of the age of the universe—and in the same neighborhood. To verify their discovery, the researchers examined previous observations from the ALMA radio telescope. They found an emission line from ionized carbon that closely matched the redshifts observed by the JWST.

The team calculated that the companion galaxy, which they named SPT0418-SE, was within 5 kiloparsecs of the ring. (The Magellanic Clouds, satellites of the Milky Way, are about 50 kiloparsecs away.) This proximity suggests that the galaxies are destined to interact with each other and even merge, an observation that contributes to understanding how early galaxies may have evolved into larger galaxies.

The two galaxies are modestly massive compared to galaxies in the early Universe, and “SE” is relatively smaller and less dusty, making it appear bluer than the ring, heavily obscured by dust. Based on images of nearby galaxies with similar colors, the researchers suggest that they could reside “in a massive halo of dark matter with neighbors yet to be discovered.” HIGH METALLICITY What was most surprising about the companion galaxy, considering its age and mass, was its mature metallicity: amounts of elements heavier than helium and hydrogen, such as carbon, oxygen, and nitrogen. The team estimated that it was comparable to that of our Sun, which is more than 4 billion years old and inherited most of its metals from previous generations of stars that took 8 billion years to accumulate. “We are seeing the remains of at least a couple of generations of stars that lived and died in the first billion years of the universe’s existence, which is not what we usually see,” says Vishwas. “We speculate that the star formation process in these galaxies must have been very efficient and started very early in the universe, especially to explain the measured abundance of nitrogen relative to oxygen, since this ratio is a reliable measure of how many generations of stars have lived and died.”