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Physicists open new windows to dark energy

Galaxy cluster density map

A celestial map showing the densities of galactic clusters, galaxies, and cosmic matter above the part of the sky surveyed by dark energy observations. The left panel shows the density of the galaxies in that part of the sky, while the center panel shows the density of matter and the right shows the galaxy cluster density. Red areas are denser and blue areas are less dense than average.Credits: Chun-Hao To / Stanford University, SLAC National Accelerator Laboratory.

For the first time, DES scientists have been able to combine measurements of galactic and galaxy clusters distribution to advance our understanding of dark energy.

The universe is expanding at an ever-increasing rate, and while no one is sure why, researchers with the Dark Energy Survey (DES) at least have a strategy for figuring it out: Diffuse galactic matter And clusters of galaxies in order to better understand what is going on.

Achieving that goal becomes a hassle. But now a team led by researchers at the Department of Energy’s SLAC National Accelerator Laboratory, Stanford University and the University of Arizona have come up with a solution. Their analysis, recently published in Physical review letterProvides a more accurate estimate of the mean density of matter as well as the bias to clump – two important parameters that help physicists examine the nature of dark matter and dark energy, the mysterious matter that Make up a large part of the universe

“It’s one of the best constraints from one of the best datasets to date,” said Chun-Hao To, lead author of the new paper and graduate student at SLAC and Stanford, who works with the Kavli Institute for Particle. Says Astrophysics and Cosmology Director Risa Wechsler.

First goal

When DES began mapping the skies in 2013, the goal was to collect four types of data: distances to certain types of supernovas or stellar explosions. Distribution of matter in the universe Distribution of galaxies And distribution of galactic clusters Each of them tells researchers something about how the universe is evolving over time.

In principle, the scientists would combine the four data sources to improve their estimates. But there are obstacles: The distribution of matter, galaxies and galaxy clusters are all closely related. If researchers don’t take these relationships into account, they’ll end up with It’s “double-count”, weighting too much on some data and not enough for others, To said.

To avoid handling all of this information incorrectly, Elisabeth Krause, an astrophysicist at the University of Arizona, and colleagues have developed a new model that can appropriately describe the connection in the distribution of three quantities: galaxies. Galaxy and cluster In doing so, they were able to create an initial analysis to properly combine these different datasets to learn about dark matter and dark energy.

Estimate adjustment

Adding that model to a DES analysis has two consequences. First of all, measuring the distribution of galactic matter and galactic clusters often results in different types of errors. Combining all three measurements makes it easier to identify such errors, making the analysis more efficient. Second, the three measurements differed in their susceptibility to mean density of matter and coagulation. As a result, combining the three can improve the accuracy with which DES can measure dark matter and dark energy.

In the new paper To, Krause and colleagues used their new method in the first year of the DES data and increased the accuracy of previous estimates for density and concentration of matter.

The team was now able to combine galactic matter and galaxy clusters simultaneously in their analysis, adding the supernova data would be fairly straightforward since that type of data was not closely related to the other three.

“The next step immediately,” he said, “is to apply the machine to DES Year 3 data, which covers more than three times the sky.” But the new data will require additional efforts to improve the model to reflect the higher quality of the newer data, To said.

“This analysis is exciting,” Wechsler said. “I expect it to set a new standard in how we can analyze data and learn about dark energy from large-scale surveys, not just for DES, but also for data. It is remarkable that we will gain from exploring the Vera Rubin Observatory’s legacy of space and time in a few years. ”

Reference: “Results of the Dark Energy Survey Year 1: Cosmological limitations from cluster abundance, weak optics and galactic affinity” by C. To et al (DES Collaboration), 6 April 2021. Physical review letter.
DOI: 10.1103 / PhysRevLett.126.141301

The research is a joint effort to explore dark energy and is funded by the National Science Foundation and the Department of Energy’s Office of Science.

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