A Tip of the Red Giant Branch Distance of $22.1 \pm 1.2$ Mpc to the Dark Matter Deficient Galaxy NGC1052-DF2 from 40 Orbits of Hubble Space Telescope Imaging

Abstract

The large and diffuse galaxies NGC 1052-DF2 and NGC 1052-DF4 have been found to have very low dark matter content and a population of luminous globular clusters. Accurate distance measurements are key to interpreting these observations. Recently, the distance to NGC 1052-DF4 was found to be 20.0 ± 1.6 Mpc by identifying the tip of the red giant branch (TRGB) in 12 orbits of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) imaging. Here we present 40 orbits of HST ACS data for NGC 1052-DF2 and use these data to measure its TRGB. The TRGB is readily apparent in the color-magnitude diagram. Using a forward model that incorporates photometric uncertainties, we find a TRGB magnitude of m F814W,TRGB = 27.67 ± 0.10 mag. The inferred distance is D TRGB = 22.1 ± 1.2 Mpc, consistent with the previous surface brightness fluctuation distances to the bright elliptical galaxy NGC 1052 . The new HST distance rules out the idea that some of NGC 1052-DF2's unusual properties can be explained if it were at ∼ 13 Mpc; instead, it implies that the galaxy's globular clusters are even more luminous than had been derived using the previous distance of 20 Mpc. The distance from NGC 1052-DF2 to NGC 1052-DF4 is well-determined at 2.1 ± 0.5 Mpc, significantly larger than the virial diameter of NGC 1052. We discuss the implications for formation scenarios of the galaxies and for the external field effect, which has been invoked to explain the intrinsic dynamics of these objects in the context of modified Newtonian dynamics.

Dynamical Friction in Nonlocal Gravity

“…For giant galaxies and clusters of galaxies, φ can at most approach α 0 w. Further discussion of these issues is contained in [18]. For recent observational advances in connection with dwarf galaxies, see [29][30][31][32][33] and the references cited therein; the prediction of NLG that there is less dark matter in dwarf galaxies seems to be consistent with these studies.…”

On the Tidal Formation of Dark Matter Deficient Galaxies

“…The lower panel plots the ratio of the enclosed DM mass to the enclosed stellar mass. The gray-shaded region indicates the 95% confidence region on this mass ratio using the constraints on the enclosed stellar mass and the total enclosed dynamical mass from (Shen et al 2021a) and 18.9 Mpc (Cohen et al 2018), respectively. Lower Panels: the line-of-sight velocity dispersion of the stars within the effective radius, 𝜎 star , as function of time.…”

“…If true, this would make DF2 and DF4 far more ordinary, similar to nearby dwarf galaxies, with no notable DM deficiency, and with normal GC luminosity functions. However, recent analyses of the tip of the red giant branch, based on deep Hubble Space Telescope photometry by Danieli et al (2020) and Shen et al (2021a), seem to confirm the larger distances, and thus the deficiency of DM in both DF2 and DF4.…”

“…For comparison, the black dashed horizontal line indicates the effective radius of DF2 for an assumed distance of 20 Mpc (van Dokkum et al 2018b). The upper and lower boundaries of the shaded region indicate the effective radius for assumed distances of 𝐷 = 22.1 Mpc(Shen et al 2021a) and 18.9 Mpc(Cohen et al 2018), respectively. Lower Panels: the line-of-sight velocity dispersion of the stars within the effective radius, 𝜎 star , as function of time.…”

“…Top panel: median projected radius, 𝑅 GC,med , of the GCs from the centre of the satellite galaxy, indicating the spatial extent of the GC distribution. For comparison, the black dashed horizontal line indicates the corresponding radius in DF2 assuming a distance of 20 Mpc (seevan Dokkum et al 2018b), while the upper and lower boundaries of the shaded region mark the corresponding radii using the distance measurements ofShen et al (2021a) andCohen et al (2018), respectively. Middle panel: line-of-sight velocity dispersion among the GCs, 𝜎 GC .…”