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Physicists open new window in dark energy

Galaxy Cluster Density Map

A map of the sky showing the density of galaxy clusters, galaxies and matter in the universe above the part of the sky observed by the Dark Energy Survey. The left panel shows the galaxy density in that part of the sky, while the middle panel shows the substance density, and the right one shows galaxy cluster density. Red areas are denser and blue areas are less dense than average. Credit: Chun-Hao To / Stanford University, SLAC National Accelerator Laboratory

For the first time, DES researchers can combine measurements of the distribution of matter, galaxies and galaxy clusters to advance our understanding of dark energy.

The universe is expanding at an ever-increasing rate, and although no one is sure why, scientists with the Dark Energy Survey (DES) at least had a strategy for finding out: They would combine measurements of the distribution of matter, galaxies, and galaxy clusters for better to understand what is going on.

Achieving this goal proved to be quite difficult, but now a team led by researchers at the Department of Energy’s SLAC National Accelerator Laboratory, Stanford University and the University of Arizona has come up with a solution. Their analysis, recently published in Physical review letters, provides more accurate estimates of the average density of matter as well as its propensity to clump together – two key parameters that help physicists study the nature of dark matter and dark energy, the mysterious substances that make up the vast majority of the universe.

“It’s one of the best limitations from one of the best datasets to date,” says Chun-Hao To, a lead author on the new paper and a graduate student at SLAC and Stanford working with the Kavli Institute for Particle Astrophysics and Cosmology. Director Risa Wechsler.

An early goal

When DES set out in 2013 to map one-eighth of the sky, the goal was to gather four kinds of data: the distances to certain types of supernovae or exploding stars; the distribution of matter in the universe; the distribution of galaxies; and the distribution of galaxy clusters. Each tells scientists something about how the universe has evolved over time.

Ideally, scientists would put all four data sources together to improve their estimates, but there is a pick: The distribution of matter, galaxies, and galaxy clusters are all closely related. If researchers do not take these factors into account, they will end up “double counting” and placing too much emphasis on some data and not enough on others, To says.

To avoid misuse of all this information, To, astrophysicist from the University of Arizona, Elisabeth Krause, and colleagues have developed a new model that could properly take into account the connections in the distribution of all three sizes: matter, galaxies, and galaxy clusters. Thus, they were able to produce the first analysis ever to correctly combine all these different data sets to learn about dark matter and dark energy.

Improving estimates

Adding this model to the DES analysis has two effects, To says. First, measurements of the distribution of matter, galaxies, and galaxy clusters tend to introduce different kinds of errors. Combining all three measurements makes it easier to identify such errors, making the analysis more robust. Second, the three measurements differ in how sensitive they are to the average density of matter and its lumpiness. As a result, combining all three can improve the precision with which DES can measure dark matter and dark energy.

In the new paper, To, Krause, and colleagues applied their new methods to the first year of DES data, sharpening the accuracy of previous estimates of the substance’s density and lumpiness.

Now that the team can incorporate matter, galaxies, and galaxy clusters simultaneously into their analysis, addition in supernova data will be relatively straightforward, as that kind of data is not so closely related to the other three, To says.

“The next immediate step,” he says, “is to apply the machines to DES Year 3 data, which has three times the coverage of the sky.” This is not as simple as it sounds: While the basic idea is the same, the new data will require further efforts to improve the model to keep up with the higher quality of the newer data, To says.

“This analysis is really exciting,” Wechsler said. “I expect it to set a new standard in the way we are able to analyze data and learn about dark energy from large studies, not only for DES, but also looking forward to the incredible data we get from Vera Rubin Observatory’s Legacy Survey of space and time in a few years. ”

Reference: “Results of dark energy study year 1: Cosmological constraints from cluster volumes, weak lensing and galaxy correlations” by C. To et al. (DES Collaboration), April 6, 2021, Physical review letters.
DOI: 10.1103 / PhysRevLett.126.141301

The research was a collaborative effort within the Dark Energy Survey and was supported by the National Science Foundation and the Department of Energy’s Office of Science.

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