ALMA Found Hidden Cosmic Fuel

An unexpected discovery made by a scientific team using data from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Path Finder Experiment (APEX) reveals diffuse molecular gas in distant galaxy protocluster, extending star formation timeline to 400 million years. 

The surprisingly large reservoir of molecular gas is located approximately 12 billion light-years away in the protocluster of galaxies known as SPT2349-56, a region of the early universe where a cluster of galaxies is just beginning to form. 

Galaxy clusters are the largest structures in the universe, and understanding their formation is a major goal of scientists. Protoclusters like SPT2349-56 offer a unique window into this process, allowing astronomers to observe galaxies as they come together in a dense environment. 

This new research, led by Dazhi Zhou of the University of British Columbia, focuses on the molecular gas within SPT2349-56. Molecular gas, primarily hydrogen, is the raw material for star formation, which plays a critical role in galaxy evolution. 

By comparing ALMA's high-resolution configuration observations with lower-resolution data from ALMA's Morita Array, a.k.a. Atacama Compact Array (ACA), and APEX, the team found a significant amount of molecular gas "invisible" in the higher-resolution ALMA images. The ACA detected 75% more CO than the sum of individual sources detected in higher-resolution ALMA data. 

This missing gas isn't just a few faint, undetected galaxies. Instead, it appears to be a diffuse reservoir of gas spread throughout the protocluster. 

This hidden gas reservoir could be the key to understanding the intense star formation activity observed in SPT2349-56. The presence of so much extra gas extends the star formation fuel, meaning the overall depletion timescale will exceed 400 million years. 

The team speculates that this extended gas might be the precursor to the hot, diffuse gas known as the intracluster medium (ICM) that fills mature galaxy clusters. 

"This discovery highlights the power of ALMA, especially when used in multiple configurations," says Zhou. "The high-resolution observations allowed us to pinpoint individual galaxies, while the lower-resolution data revealed the bigger picture – the extended gas that connects these galaxies and fuels their star formation."  

SPT2349-56 is an extreme system, producing stars 10.000 times faster than our Milky Way, and these observations have pushed scientists' understanding of galaxy formation and evolution. No simulation or galaxy formation model had previously predicted this overdensity of gas. These findings also suggest that high-resolution ALMA observations, while excellent for studying individual galaxies, may miss a significant gas component in these early clusters. The missing gas may reside in the circum-galactic medium (CGM) or the pre-heated proto-intracluster medium (proto-ICM). 

Future studies using ALMA's full capabilities, including its compact array configurations, will be crucial for fully characterizing this hidden gas reservoir and understanding its role in forming galaxy clusters. 

Additional Information 

The results of the observations are published in the following scientific paper: "A Large Molecular Gas Reservoir in the Protocluster SPT2349−56 at z=4.3" by Zhou et al. 

The original press release was published by the National Radio Astronomical Observatory (NRAO) of the United States, an ALMA partner on behalf of North America.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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