Researchers uncover dark matter dominance in early universe galaxies
The study builds on the pioneering work of astronomer Vera Rubin, who in the 1970s observed that the outer regions of nearby galaxies were rotating faster than expected, leading to the identification of a flat rotation curve. Under Newtonian mechanics, the velocity of objects farther from a galaxy's center should decrease. However, Rubin's observations suggested the presence of an invisible mass-dark matter-encompassing galaxies in a halo, influencing their rotation speeds. Despite its fundamental role in cosmology, the formation and distribution of dark matter in the distant universe remain largely unexplored.
Led by visiting researcher Qinyue Fei of the University of Tokyo's Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) and graduate student at Peking University, the research team included Kavli IPMU Professor John Silverman, University of Texas at Austin researcher Dr. Seiji Fujimoto, and Peking University's Kavli Institute for Astronomy and Astrophysics Associate Professor Ran Wang. The team investigated the dark matter content surrounding two supermassive black holes in galaxies from the early universe.
"Vera Rubin provided the first evidence for dark matter using rotation curves in nearby galaxies. We are applying the same approach, but to galaxies in the early universe," Silverman explained.
Utilizing data from the Atacama Large Millimeter/submillimeter Array (ALMA) and observations of the ionized carbon (C+) emission line, the researchers analyzed the gas dynamics in two quasar host galaxies at redshift 6. By studying the galaxies' rotation curves, they determined that dark matter constituted around 60% of the total mass.
The velocity distribution within these galaxies was examined through shifts in gas motion, with blue-shifted gas moving toward the observers and red-shifted gas moving away. Previous studies suggested that galaxies from this era exhibited declining rotation curves at their outskirts, implying a lower presence of dark matter. However, the data gathered by Fei and Silverman's team demonstrated a flat rotation curve, resembling those found in massive disk galaxies near Earth. This indicates a greater proportion of dark matter was needed to account for the high observed velocities.
These findings offer a deeper understanding of the complex relationship between dark matter and supermassive black holes, contributing to broader research on galaxy formation and evolution from the universe's infancy to the present day.
Research Report:Assessing the dark matter content of two quasar host galaxies at z~6 through gas kinematics
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Kavli Institute for the Physics and Mathematics of the Universe
Stellar Chemistry, The Universe And All Within It
