Cosmic web connecting the universe forms dark matter in galaxies

(ORDO NEWS) — Galaxies located at the “nodes” of the cosmic web collect dark matter earlier and are more enriched in heavy elements than those further away.

Our Universe is connected by a cosmic web of giant filaments of dark matter and gas that stretch for millions of light-years and intersect at “nodes” inhabited by dense clusters of galaxies.

This vast network is shaping the distribution and evolution of galaxies in fundamental ways that scientists are trying to unravel with increasingly precise observations and advanced simulations.

Now a team led by Callum Donnan, a PhD student in astronomy at the University of Edinburgh, has identified a key correlation between the chemical composition of galaxies and their location in the cosmic web.

Using both real observations and computer simulations, the team found that “galaxies closer to the nodes [show] higher chemical enrichment than those farther away.” The discovery reveals some of the mysterious dynamic processes that bind the universe, according to a study published Monday in the journal Nature Astronomy.

“It has long been assumed that there is a relationship between how galaxies evolve and their position in the cosmic web,” Donnan said in an email.

“However, it has been difficult to obtain observational evidence because of the need to conduct large, dense spectroscopic surveys covering a large part of the sky. The results of such observations are recent, but how the properties of the gas are related to the cosmic web has not been studied in sufficient detail before.”

To answer this question, Donnan and colleagues studied galaxies within about a billion light-years of the Milky Way as observed by the Sloan Digital Sky Survey in New Mexico, which covers a vast region of the sky. The team studied the elemental composition of gases in the interstellar space of these real galaxies, a property known as gas phase metallicity.

The results showed that galaxies located near the nodes of the cosmic web were richer in “metals”, which in astronomy means any element heavier than helium.

A weak correlation was also observed with proximity to the threads of the web – the threads that stretch through the entire Universe and connect the knots together. The team performed complex cosmological simulations using the IllustrisTNG platform, which confirmed the observations.

Importantly, the approach showed that the position of a galaxy in the cosmic web changes its chemical abundance even when other factors, such as the density of a particular region of the universe, are taken into account.

“We suspected that such a connection exists, since galaxies are not isolated systems and interact with their environment,” Donnan said.

“However, we weren’t sure what to expect, as there are numerous physical processes at work here. There has been some evidence in the past that galaxies in superdense regions of the universe are chemically enriched, but nothing points to the full scale of the cosmic web.”

Naturally, the question arises why galaxies located near the nodes are enriched in a large amount of metals compared to galaxies located along filaments or in empty “voids” of the cosmic web. Donnan’s team identified two main drivers of this relationship: the absorption of gas from the outside of galaxies and the evolution of stars and dark matter within them.

Galaxies feed on gases that are scattered throughout space in the intergalactic medium, but those farther from the nodes consume much more of this external material than those close to the nodes.

Since the intergalactic gas is poor in metals, it dilutes the enriched gas of distant galaxies, reducing their overall metallicity in the gas phase. Galaxies near nodes do not consume as much of this metal-poor material, which helps them remain chemically enriched in higher concentrations of heavy elements.

In addition, galaxies near the nodes seem to have matured earlier than galaxies further away. These galaxies had an advantage in the birth of new stars and the collection of dark matter – the mysterious substance that makes up most of the matter in the universe.

“We think that galaxies near the nodes had more star formation in the past, and other results show that galaxies near the nodes collected their dark matter earlier,” Donnan said. “We hypothesize that this shows a link between the underlying assembly of the large structure of dark matter in the universe and the metallicity of the gas through increased early star formation.”

Figuring out these subtle connections between the cosmic web and galaxy evolution is a difficult task given the scale and complexity of these astronomical interactions. Donnan and colleagues said their results represent “an important first step towards this goal” in the study, but they also emphasize that new technologies will allow these mysteries to be clarified in the future.

In particular, the Dark Energy Spectroscopic Instrument (DESI), due to be completed in the mid-2020s, will help uncover some of the hidden connections between this epic cosmic structure and the galaxies in and around it.

“With the Dark Energy Spectroscopic Instrument (DESI), we’ll get spectra of an order of magnitude more galaxies, which will allow us to move this question forward and start really unraveling how the cosmic web influences the evolution of galaxies,” Donnan said. “DESI will also allow us to see this effect in the more distant past, which means we can see how the role of the cosmic web in the evolution of galaxies changes over time.”

“The overall picture here is to try to create a complete picture of the evolution of galaxies, and we have shown that for this we need to take into account the role of the cosmic web,” he concluded. ‚ÄúThere is a lot of uncertainty, especially around the complex gaseous physics of galaxies, and we have shown that the cosmic network plays a role in this.

Also, trying to relate how the large-scale structure of the universe grows to how galaxies evolve is important for understanding evolution. The universe as a whole, because it can help us better understand cosmology. It helps create a bridge between physics on the largest scales and on the smaller, galactic scales.”

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