Did water exist in the galaxies of the early cosmos? (Holiday feature)

The first Galaxy SPT0311-58

It has been said that to understand water is to understand the cosmos and life itself. Observations in 2021 by the Atacama Large Millimeter/submillimeter Array (ALMA) detected this primordial substance in the most massive galaxy in the early Universe.

Scientists studying ALMA data from SPT0311-58 found water molecules H2O, along with carbon monoxide in the galaxy, which is about 12.88 billion light-years from Earth. The detection of these two molecules in abundance suggests that the molecular universe was going strong shortly after the elements were forged into the first stars. The research includes the most detailed study of the molecular gas content of a galaxy in the early universe to date and the most distant detection of H2O in a normal star-forming galaxy. The research was published in The Astrophysical Journal.

Two galaxies merging into a giant elliptical?

SPT0311-58 actually consists of two galaxies and was first seen by ALMA scientists in 2017 at its location, or time, in the Epoch of Reionization. This epoch occurred at a time when the universe was only 780 million years old, about 5 percent of its current age, and the first stars and galaxies were being born. Scientists believe that the two galaxies may merge and that their rapid star formation is not only consuming their gas, or star-forming fuel, but could eventually evolve the pair into massive elliptical galaxies like those seen in the local universe.

These molecules, important for life on Earth, are forming as soon as possible and their observation allows us to better understand the structural formation and evolution of the early universe”.

This artist’s image above shows the continuum of dust and molecular lines of carbon monoxide and water observed in the galaxy pair known as SPT0311-58. Data from the ALMA Observatory reveal abundant CO and H2O in the larger of the two galaxies, indicating that the molecular Universe was going strong shortly after the elements were initially forged. Credit: ALMA (ESO/NAOJ/NRAO)/S. lamb (NRAO)

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A high redshift

“Using ALMA’s high-resolution observations of molecular gas in the pair of galaxies known collectively as SPT0311-58, we detected both water and carbon monoxide molecules in the larger of the two galaxies. Oxygen and carbon, in particular, are first-generation elements and, in the molecular forms of carbon monoxide and water, are fundamental to life as we know it,” said Sreevani Jarugula, an astronomer at the University of Illinois and principal investigator on the new research.”This galaxy is the most massive currently known high-redshift galaxy, or the time when the universe was still very young. It has more gas and dust than other galaxies in the early universe , which offers us many potential opportunities to observe abundant molecules and to better understand how these life-creating elements influenced the development of the early universe.”

The ALMA Observatory detects water in the first galaxies

These science images show the molecular lines and dust continuum seen in ALMA observations of the pair of early massive galaxies known as SPT0311-58. Left: A composite image combining the dust continuum with molecular lines for H2O and CO. Right: Dust continuum seen in red (top), molecular line for H2O shown in blue (2nd from top), molecular line transitions for carbon monoxide, CO(rotation states 6 to 5 ) shown in purple (middle), CO( 7-6) shown in magenta (second from bottom), and CO(10-9) shown in pink and deep blue (bottom). The different molecules and transitions track different densities of the gas in those galaxies. Credit: ALMA (ESO/NAOJ/NRAO)/S. lamb (NRAO)

The first galaxies are forming stars thousands of times faster than the Milky Way.”

Water, in particular, is the third most abundant molecule in the universe after molecular hydrogen and carbon monoxide. Previous studies of galaxies in the local and early universe have correlated the emission of water and the far-infrared emission from dust.

The dust helped detect water emissions

“The dust absorbs ultraviolet radiation from stars in the galaxy and re-emits it as far-infrared photons,” Jarugula said. “This further excites the water molecules, resulting in the emission of water that scientists are able to observe. In this case, it helped us detect water emissions in this huge galaxy. This correlation could be used to develop water as a tracer of star formation, which could then be applied to galaxies on a cosmological scale.”

Studying the first galaxies that formed in the universe helps scientists better understand the birth, growth and evolution of the universe and everything in it, including the solar system and the Earth. To detect such significant emissions from molecules in very distant galaxies, the first generation of stars not only needed to synthesize heavier elements such as oxygen and carbon, but there also had to be large pockets of cold, high-density gas inside of these galaxies so that the atoms could combine into molecules.

“The first galaxies are forming stars thousands of times faster than the Milky Way,” Jarugula said. “Studying the gas and dust content of these early galaxies informs us about their properties, such as how many stars are forming, the rate at which gas is being converted into stars, how the galaxies interact with each other and with the interstellar medium, and even more .”

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How did so much gas and dust assemble?

According to Jarugula, there is still a lot to learn about SPT0311-58 and the galaxies of the early universe. “Not only does this study provide answers to where and how far away water may exist in the universe, it has also raised a big question: How did so much gas and dust assemble to form stars and galaxies so early in the universe? ? The answer requires further studies of these and similar star-forming galaxies to gain a better understanding of the structural formation and evolution of the early universe.”

In an email to The Galaxy newspaper, Jarugula wrote: “The dust consists mainly of asymptotic giant branch (AGB) stars and supernovae. On the surface of the powder, many chemical processes occur that form molecules. Early universe theory and modeling are trying to figure out why such early galaxies have so much dust. This is an active area of ​​research, and next-generation telescopes like JWST will probe further out into the Universe and hopefully provide more answers.”

“This exciting result, which shows the power of ALMA, adds to a growing collection of observations of the early universe,” said Joe Pesce, astrophysicist and ALMA program director at the National Science Foundation. “These molecules, important for life on Earth, are forming as soon as possible, and their observation is giving us an idea of ​​the fundamental processes of a universe very different from today.”

More information: Observations of molecular lines in two dusty star-forming galaxies at z = 6.9, S. Jarugula et al., 2021.

Maxwell Moastrophysicist, NASA Einstein Fellow, University of Arizona through the Alma Observatory, Sreevani Yarugula And National Radio Astronomy Observatory

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