Figure 1. Left: Gas distribution of ionized carbon (C+) on the halo scale of P009-10 as shown by the color image and black contours. Nuclear gas distribution, centered on the quasar (large black cross), is shown by the magenta contours. Right: Velocity field of the C+ emission from -200 (in blue; moving towards us) to +200 (in red; moving away from us) km/s indicating coherent rotation in a massive dark matter halo. (Credit: Fei et al. 2025, ApJ, 980, 84)
An international team of researchers led by Peking University PhD student Qinyue Fei has found dark matter dominating the halos of two supermassive black holes in galaxies roughly 13 billion light years away, reports a new study published in The Astrophysical Journal on 5 February 2025.
Their study gives new insight into the relationship between dark matter and supermassive black holes when the universe was still very young, and how galaxies have evolved until today.
The first person to discover that dark matter played an important role in galaxies was astronomer Vera Rubin, who in the 1970s noticed that the outer parts of local galaxies were rotating at higher speeds than expected, forming what was later named a flat rotation curve. If galaxies were only made up of stars and gas and obeyed Newton's laws, the outskirts of a galaxy would move slower than the peak velocity closer to the galaxy’s center. Rubin’s observations could only make sense if there were a large amount of invisible mass, later called dark matter, that surrounded the galaxy like a halo, allowing stars and gas anywhere far from the galaxy center to move at higher velocity. Furthermore, dark matter assembly so far back in the universe has never been observationally constrained and remains unknown, despite its fundamental importance to our understanding of the Universe.
A research team led by a graduate student Qinyue Fei from the Kavli Institute for Astronomy and Astrophysics at Peking University (KIAA, PKU) who was visiting the University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), and including Kavli IPMU Professor John Silverman, the University of Texas Austin’s Dr. Seiji Fujimoto, and Peking University Department of Astronomy & KIAA Associate Professor Ran Wang, KIAA University Chair Professor Luis Ho, have studied the dark matter content of supermassive black holes about 13 billion light years away.
“Vera Rubin provided the first evidence for dark matter using the rotation curves of nearby local galaxies. We’re using the same technique but now in the early universe,” said Silverman.
“Our study demonstrates that gas dynamics traced by ALMA observations hold significant potential in probing the dark matter of quasar host galaxies during the cosmic dawn,” said Qinyue, the first author of the paper.
Made possible using data from the Atacama Large Millimeter/submillimeter Array (ALMA) and the ionized carbon (C+) emission line, the researchers were able to uncover the gas dynamics of two quasar host galaxies at redshift 6. By studying the rotation curves of each galaxy (Figure 2), they found dark matter made up about 60 per cent of its total mass.
Velocity changes with radius in the galaxy are captured by blue-shifted gas (moving towards the researchers), and the red-shifted gas (moving away) (Figure 1).Interestingly, the rotation curves in the distant universe from past studies reveal a decrease in the galaxy outskirts, meaning a low fraction of dark matter. But the data taken by Fei and Silverman’s team shows a flat rotation curve, similar to the massive disk galaxies close to Earth, which indicates more dark matter is required to explain the high velocities (Figure 2).
The team's findings shed light on the intricate relationship between dark matter and supermassive black holes. They offer a crucial piece of the puzzle in understanding how galaxies evolved from the early universe to the structures we observe today.
Figure 2. Rotation curves of distant galaxies. Fei et al. data, in red and blue, remains relatively flat (i.e., high), similar to local massive disk galaxies at z~0 (dashed grey line) that need extended dark matter to explain their high velocities. The results from other galaxies at redshift~2-3 (in gray data points) show a rotation curve that decreases at the outskirts. This leads to a low dark matter fraction. (Credit: Fei et al. 2025, ApJ, 980, 84)
Paper details
Journal: The Astrophysical Journal
Paper title: Assessing the dark matter content of two quasar host galaxies at z∼6 through gas kinematics
Authors: Qinyue Fei (1, 2, 3), John Silverman (1, 4, 5, 6), Seiji Fujimoto (7), Ran Wang (3, 2), Luis C. Ho (3, 2), Manuela Bischetti (8, 9), Stefano Carniani (10), Michele Finolfi (11, 12), Gareth Jones (13), Roberto Maiolino (14, 15, 16), Wiphu Rujopakarn (17, 18), N. M. Förster Schreiber (19), J. Espejo (19), L. L. Lee (19)
Author affiliations:
1 Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI), UTIAS, Tokyo Institutes for Advanced Study,University of Tokyo, Chiba, 277-8583, Japan
2 Department of Astronomy, School of Physics, Peking University, Beijing 100871, P. R. China
3 Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, P. R. China
4 Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
5 Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
6 Center for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
7 Department of Astronomy, The University of Texas at Austin, Austin, TX, USA
8 Dipartimento di Fisica, Universit´a di Trieste, Sezione di Astronomia, Via G.B. Tiepolo 11, I-34131 Trieste, Italy
9 INAF - Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, I–34131 Trieste, Italy
10 Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
11 Dipartimento di Fisica e Astronomia, Universit`a di Firenze, Via G. Sansone 1, I-50019, Sesto F.no (Firenze), Italy
12 INAF — Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Florence, Italy
13 Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
14 Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
15 Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
16 Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK
17 National Astronomical Research Institute of Thailand, Don Kaeo, Mae Rim, Chiang Mai 50180, Thailand
18 Department of Physics, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Pathumwan, Bangkok 10330, Thailand
19 Max-Planck-Institut f¨ur extraterrestrische Physik (MPE), Giessenbachstr. 1, D-85748 Garching, Germany
DOI: 10.3847/1538-4357/ada145 (Published 5 February 2025)
Link to the Journal paper:https://doi.org/10.3847/1538-4357/ada145
Pre-print (arXiv.org): https://arxiv.org/abs/2501.09077
Kavli IPMU news link: https://www.ipmu.jp/en/20250207-darkmatter
Research contact
John Silverman
Professor
Kavli Institute for the Physics and Mathematics of the Universe
E-mail: john.silverman@ipmu.jp
Local contact
Qinyue Fei
PhD student
Department of Astronomy, School of Physics, Peking University
Kavli Institute for Astronomy and Astrophysics, Peking University
E-mail: qyfei@pku.edu.cn
