To achieve these results, Montes et al. use very deep optical observations to reach a sensitivity limit of 30.4 mag arcsec–2 in the g band. This dataset probes the surface brightness of the galaxy out to around 80 arcsec (which corresponds to distances of roughly 5 to 7 kpc, depending on the distance of NGC 1052-DF2 from us), revealing a spectacularly undisturbed morphology (surface brightness contours pictured in the left panel). The authors further consider in which regions they would expect to see any tidal features, were the galaxy bound and interacting with one of its massive neighbours, NGC 1052 and NGC 1042 (pictured respectively as magenta and cyan in the right panel). They find that those regions are well observable with the sensitivity of their data and thus conclude that tidal stripping cannot explain the apparent deficit of dark matter.
The plot thickens, however, when Montes et al. turn their attention to the radial surface brightness profile. Their exquisite and wide-field data allow them to reveal an exponential decline that is indicative of a disky structure. The presence of a disk in NGC 1052-DF2 is further supported by the analysis of globular cluster kinematics in the system. Based on their surface brightness modelling and the rotation component measured previously, the authors recalculate the dynamical mass of the galaxy and find it to be 1.5 to 2.6 times larger than previously thought. In other words, these new observations seem to indicate that there is ‘room’ in the dynamical mass budget for more dark matter. With this update, the system aligns itself well with ΛCDM expectations, thus not requiring special accommodations or a modification to ΛCDM itself.
This is a preview of subscription content, access via your institution