2020ApJ...895L...4D

Previous studies have shown that the large, diffuse galaxies NGC 1052-DF2 and NGC 1052-DF4 both have populations of unusually luminous globular clusters as well as a very low dark matter content. Here we present newly obtained deep Hubble Space Telescope Advanced Camera for Surveys imaging of one of these galaxies, NGC 1052-DF4. We use these data to measure the distance of the galaxy from the location of the tip of the red giant branch (TRGB). We find a rapid increase in the number of detected stars fainter than m_F814W ∼ 27.3, which we identify as the onset of the red giant branch. Using a forward modeling approach that takes the photometric uncertainties into account, we find a TRGB magnitude of m_F814W,TRGB=27.47±0.16. The inferred distance, including the uncertainty in the absolute calibration, is D_TRGB = 20.0 ± 1.6 Mpc. The TRGB distance of NGC 1052-DF4 is consistent with the previously determined surface brightness fluctuation distance of D_SBF = 18.7 ± 1.7 Mpc to NGC 1052-DF2 and is consistent with the distance of the bright elliptical galaxy NGC 1052. We conclude that the unusual properties of these galaxies cannot be explained by distance errors.