A galaxy lacking dark matter

Area of Science:

• Astronomy and Astrophysics
• Cosmology
• Galaxy Formation and Evolution

Background:

• The standard cosmological model posits a tight coupling between dark matter halo mass and stellar mass in galaxies.
• This relationship, quantified by the M_halo/M_stars ratio, typically shows a minimum for Milky Way-like galaxies and increases for both lower and higher mass galaxies.
• The scatter in this mass-coupling relation is poorly constrained, especially for dwarf galaxies.

Purpose of the Study:

• To investigate the dark matter content of the ultra-diffuse galaxy NGC1052-DF2.
• To test the universality of the dark matter halo-to-stellar mass coupling.

Main Methods:

• Measuring the radial velocities of ten luminous globular-cluster-like objects within NGC1052-DF2.
• Inferring the galaxy's velocity dispersion from these measurements.
• Estimating the total mass of NGC1052-DF2 within a specific radius.

Main Results:

• The velocity dispersion of NGC1052-DF2 was found to be less than 10.5 km/s (90% confidence).
• The total mass within 7.6 kpc was determined to be less than 3.4 × 10⁸ solar masses.
• This results in an M_halo/M_stars ratio of approximately unity, significantly lower (factor of at least 400) than expected.

Conclusions:

• NGC1052-DF2 exhibits an exceptionally low dark matter content relative to its stellar mass.
• This observation provides strong evidence against a universal coupling between dark matter and baryonic matter on galactic scales.
• The findings necessitate a re-evaluation of galaxy formation models within the cold dark matter paradigm.