News Releases | Research | Science
August 14, 2024
Image of Abel 2218, a dense galaxy cluster about 2 billion light-years from Earth.NASA/ESA/Johann Richard
For decades, scientists have known that some galaxies reside in dense environments, with many nearby galaxies. Others go through the universe essentially alone, with few or no other galaxies in the corner of the universe.
A new study has found one major difference between galaxies in these contrasting systems: galaxies with more distant neighbors have similar shapes and masses, but live in less dense environments. A Paper The galaxies found in the densest regions of the universe are 25% larger, researchers from the University of Washington, Yale University, the Leibniz Institute for Astrophysics in Potsdam, Germany, and Waseda University in Japan report in the Aug. 14 issue of the Astrophysical Journal. Isolated galaxies.
Research that used a new machine learning tool to analyze millions of galaxies is helping to resolve a long-standing debate among astrophysicists about the relationship between a galaxy’s size and its environment. These findings raise new questions about how galaxies form and evolve over billions of years.
„Current theories of galaxy formation and evolution cannot adequately explain the discovery of larger than homogeneous galaxies in less dense regions of the Universe,” said the lead author. Arithra GhoshUW Postdoctoral Researcher in Astronomy and For LSST-DA Catalyst Fellow with UW DiRAC Company. „That’s one of the really interesting things about astrophysics. Sometimes what theories predict we should find and what a survey actually finds don’t agree, so we go back and try to change existing theories to better explain the observations.
Past studies looking at the relationship between galaxy size and environment have come up with conflicting results. Some have determined that galaxies in clusters are smaller than isolated galaxies. Others came to the opposite conclusion. Studies were generally small-scale, based on observations of hundreds or thousands of galaxies.
In this new study, Ghosh and his colleagues used a survey of millions of galaxies. Subaru telescope In Hawaii. This effort is called HYPER SUPREME-GAM Subaru Strategic PlanHe took high quality images of each constellation. The team selected nearly 3 million galaxies with the highest quality data and used machine learning algorithms to determine the size of each. Next, the researchers essentially placed a circle around each galaxy — a circle with a radius of 30 million light years. The circle represents the immediate vicinity of the galaxy. They asked a simple question: How many neighboring galaxies are within that circle?
The answer showed a clear general trend: galaxies with more neighbors were also larger on average.
There could be many reasons for that. Dense cluster galaxies may be massive when they first form or undergo efficient mergers with close neighbors. Perhaps dark matter — the mysterious substance that makes up most of the matter in the universe but cannot be directly detected in any current form — plays a role. After all, galaxies form in individual „halos” of dark matter and the gravitational force from those haloes plays a key role in how galaxies form.
„Theoretical astrophysicists need to carry out detailed studies using simulations to establish with certainty why galaxies with neighbors are so large,” Ghosh said. „For now, we are convinced that this relationship exists between the interstellar environment and the size of the galaxy.”
Images of galaxies of various shapes and sizes. New research shows that galaxies with nearest neighbors tend to be larger.NAOJ/NASA/ESA/CSA
Using an incredibly large dataset like the Hyper Suprime-Cam Subaru Strategic Program helped the team reach a clear conclusion. But that’s only part of the story. The novel machine learning tool they used to determine the size of each galaxy also accounts for the inherent uncertainties in galaxy size measurements.
„An important lesson we learned prior to this study is that we don’t need to study a large number of galaxies to solve this question,” Ghosh said. „You need careful statistical analysis. Part of that comes from machine learning tools that can accurately quantify the uncertainty in measurements of galaxy properties.
The machine learning tool they used is called GaMPEN – or Galaxy Morphology Posterior Estimation Network. As a doctoral student at Yale, Ghosh led the development of Kampen, which was published in published papers. 2022 And 2023 In The Astrophysical Journal. The tool is freely available online and can be adapted to analyze other large studies, Ghosh said.
Although this new study focuses on galaxies, it foreshadows the type of research — centered on complex analyzes of incredibly large datasets — that will soon be hit by an astronomical storm. A new generation of telescopes with powerful cameras, incl Vera C. Rubin Observatory In Chile, come online, and they collect huge amounts of data about the cosmos every night. In anticipation, scientists are developing new tools, such as GaMPEN, that can use these large datasets to answer pressing questions in astrophysics.
„Very soon, large datasets will be the norm in astronomy,” Ghosh said. „This study is a perfect demonstration of what you can do with the right tools — when you have them.”
Co-authors of the study Urry meProfessor of Physics and Astronomy at Yale; Meredith Powella research fellow at the Leibniz Institute; Rhythm ShimakawaAssociate Professor at Waseda University; Frank van den BoschYale Professor of Astronomy; Daisuke NagaiProfessor of Physics and Astronomy at Yale; Gaustav Mitradoctoral student at Yale; And Andrew ConnollyProfessor of Astronomy at the UW and a faculty member at the DiRAC Institute and eScience Institute. The research was funded by NASA, the Yale Graduate School of Arts and Sciences, the John Templeton Foundation, the Charles and Lisa Simoni Endowment for the Arts and Sciences, the Washington Research Foundation, and the UW eScience Institute.
For more information, contact Kosh at [email protected].
Tag(s): Arithra Ghosh • Astronomy & Astrophysics • College of Arts and Sciences • Department of Astronomy • DIRAC Institute