Effects of mass models on dynamical mass estimate: the case of ultra diffuse galaxy NGC1052-DF2

TL;DR

This study examines how different tracer profile models affect the dynamical mass estimates of the ultra diffuse galaxy NGC1052-DF2, highlighting significant uncertainties due to modeling choices and small sample sizes.

Contribution

It demonstrates that the choice of tracer density profiles significantly impacts the dynamical mass estimates, emphasizing the importance of modeling assumptions in dark matter assessments.

Findings

Power-law model yields similar mass limits as previous studies.

Sérsic model results in higher mass-to-light ratio estimates.

Mass estimates remain uncertain due to small kinematic samples and model dependence.

Abstract

NGC1052-DF2 was recently discovered as the dark-matter deficient galaxy claimed by van Dokkum et al. (2018a, vD18). However, large uncertainties on its dynamical mass estimate have been pointed out, concerning the paucity of sample, statistical methods and distance measurements. In this work, we discuss the effects of the difference in modeling of the tracer profile of this galaxy on the dynamical mass estimate. To do this, we assume that the tracer densities are modeled with power-law and S\'ersic profiles, and then we solve the spherical Jeans equation to estimate the dynamical mass. Applying these models to kinematic data of globular clusters in NGC1052-DF2, we compare 90 per cent upper limits of dynamical mass-to-light ratios estimated between from this analysis and from vD18. We find that the upper limit obtained by the power-law is virtually the same as the result from vD18, whilst this limit estimated by the S\'ersic is significantly greater than that from vD18, thereby suggesting that NGC1052-DF2 can still be a dark-matter dominated system. Consequently, we propose that dynamical mass estimate of a galaxy is largely affected by not only small kinematic sample but the choice of tracer distributions, and thus the estimated mass still remains quite uncertain.