Dark matter-baryons separation at the lowest mass scale: the Bullet Group

TL;DR

This study reports the first detection of dark matter-baryons separation in a low-mass galaxy group, providing insights into dark matter interactions and suggesting such phenomena are more common than previously thought.

Contribution

It presents the lowest mass galaxy group with observed dark matter-baryons separation, offering new constraints on dark matter interaction cross sections.

Findings

Detected a 124 kpc separation between gas and dark matter in a low-mass group.

Estimated an upper limit of 10 cm^2 g^{-1} for dark matter interaction cross section.

Indicates that bullet-like dark matter phenomena are not limited to massive mergers.

Abstract

We report on the X-ray observation of a strong lensing selected group, SL2S J08544-0121, with a total mass of $2.4 \pm 0.6 \times 10^{14}$ $\rm{M_\odot}$ which revealed a separation of $124\pm20$ kpc between the X-ray emitting collisional gas and the collisionless galaxies and dark matter (DM), traced by strong lensing. This source allows to put an order of magnitude estimate to the upper limit to the interaction cross section of DM of 10 cm$^2$ g$^{-1}$. It is the lowest mass object found to date showing a DM-baryons separation and it reveals that the detection of bullet-like objects is not rare and confined to mergers of massive objects opening the possibility of a statistical detection of DM-baryons separation with future surveys.