The Distance of the Dark Matter Deficient Galaxy NGC1052-DF2

TL;DR

This paper reevaluates the distance to the dark matter deficient galaxy NGC1052-DF2, demonstrating that previous estimates based on the tip of the red giant branch were affected by blending effects, and provides a new distance measurement consistent with prior results.

Contribution

The study shows that blending effects can bias TRGB-based distance estimates and offers a new, calibration-independent distance measurement using a megamaser-TRGB-SBF distance ladder.

Findings

Blending causes a 'phantom' TRGB 2 times brighter, leading to underestimated distances.

No evidence of the expected RGB star population at 13 Mpc.

New distance measurement of 18.7 ± 1.7 Mpc consistent with previous estimates.

Abstract

We recently inferred that the galaxy NGC1052-DF2 has little or no dark matter and a rich system of unusual globular clusters. We assumed that the galaxy is a satellite of the luminous elliptical galaxy NGC1052 at ~20 Mpc, on the basis of its surface brightness fluctuations (SBF) distance of $19.0 \pm 1.7$ Mpc, its radial velocity of ~1800 km/s, and its projected position. Here we analyze the color-magnitude diagram (CMD) of NGC1052-DF2, following the suggestion by Trujillo et al. (2018) that the tip of the red giant branch (TRGB) can be detected in currently available HST data and the galaxy is at ~13 Mpc. Using fully populated galaxy models we show that the CMD is strongly influenced by blends. These blends produce a "phantom" TRGB ~2 times brighter than the true TRGB, which can lead to erroneous distance estimates ~1.4 times smaller than the actual distance. We compare NGC1052-DF2 to model images as well as other galaxies in our HST sample, and show that the large population of unblended RGB stars expected for distances of ~13 Mpc is not detected. We also provide a new distance measurement to NGC1052-DF2 that is free of calibration uncertainties, by anchoring it to a satellite of the megamaser host galaxy NGC4258. From a megamaser-TRGB-SBF distance ladder we obtain $D=18.7 \pm 1.7$ Mpc, consistent with our previous measurement and with the distance to the elliptical galaxy NGC1052.