2026-06-16 イェール大学
The inset image shows Hubble Space Telescope imaging of DF9, the third “galaxy without dark matter” along a trail of galaxies (Keim et al. 2026). The background shows the full trail of galaxies, including the first two galaxies without dark matter, DF2 and DF4. (DECaLS)
＜関連情報＞
- https://news.yale.edu/2026/06/16/third-times-charm-row-faint-galaxies-without-dark-matter
- https://iopscience.iop.org/article/10.3847/1538-4357/ae6b8d
NGC 1052領域の銀河群に沿って、暗黒物質を欠く3つ目の銀河が発見された A Third Galaxy Missing Dark Matter along a Trail of Galaxies in the NGC 1052 Field
Michael A. Keim, Pieter van Dokkum, Zili Shen, Shany Danieli, and Imad Pasha
The Astrophysical Journal Published: 2026 June 16
DOI:10.3847/1538-4357/ae6b8d
Abstract
While most dwarf galaxies are strongly dark-matter-dominated, two remarkable objects in the NGC 1052 field, DF2 and DF4, appear to lack dark matter. DF2 and DF4 were recently found to be part of a trail of low-luminosity galaxies that follow a linear relation between their position and radial velocity. If the other galaxies on this trail formed together with DF2 and DF4, e.g., from gas that was separated from dark matter through a “bullet dwarf” collision, they may lack dark matter as well. Here, we constrain the mass of DF9, the galaxy on the trail that most closely resembles DF2 and DF4. Using Keck/KCWI we find that DF9’s stellar velocity dispersion is 6.5+3.9-4.3 km s−1. This is consistent with the8.3+0.9-1.4 km s−1 dispersion that is expected from DF9’s 1.4 × 108 M⊙ stellar mass alone, and we conclude that—like DF2 and DF4—dark matter is not required to explain the kinematics of DF9. The dispersion is far below the 24 ± 3 km s−1 expected if DF9 had a 1.4 × 1010 M⊙ dark matter halo falling on the stellar mass–halo mass relation. We demonstrate that these results are not sensitive to the assumed distance of the trail. Our results are further evidence that the trail of low-mass galaxies in the NGC 1052 field formed together in a unique galaxy formation channel, and are consistent with the prediction of the bullet dwarf scenario that other trail galaxies should show the same lack of dark matter as DF2 and DF4.
