The central dark matter distribution of NGC 2976

TL;DR

This study investigates the dark matter distribution in NGC 2976, finding that stellar kinematics favor a cuspy halo, challenging previous claims of a cored profile based on gas kinematics.

Contribution

It demonstrates that stellar kinematic analysis can reveal a cuspy dark matter halo in NGC 2976, contrasting with gas-based measurements and highlighting the importance of assumptions in kinematic modeling.

Findings

Stellar kinematics favor a cuspy dark matter halo.

Gas kinematics are inconsistent with stellar kinematics due to assumptions.

Relaxing assumptions in gas analysis aligns results with stellar kinematics.

Abstract

We study the mass distribution in the late-type dwarf galaxy NGC 2976 through stellar kinematics obtained with the VIRUS-P integral-field spectrograph and anisotropic Jeans models as a test of cosmological simulations and baryonic processes that putatively alter small-scale structure. Previous measurements of the H-alpha emission-line kinematics have determined that the dark matter halo of NGC 2976 is most consistent with a cored density profile. We find that the stellar kinematics are best fit with a cuspy halo. Cored dark matter halo fits are only consistent with the stellar kinematics if the stellar mass-to-light ratio is significantly larger than that derived from stellar population synthesis, while the best-fitting cuspy model has no such conflict. The inferred mass distribution from a harmonic decomposition of the gaseous kinematics is inconsistent with that of the stellar kinematics. This difference is likely due to the gas disk not meeting the assumptions that underlie the analysis such as no pressure support, a constant kinematic axis, and planar orbits. By relaxing some of these assumptions, in particular the form of the kinematic axis with radius, the gas-derived solution can be made consistent with the stellar kinematic models. A strong kinematic twist in the gas of NGC 2976's center suggests caution, and we advance the mass model based on the stellar kinematics as more reliable. The analysis of this first galaxy shows promising evidence that dark matter halos in late-type dwarfs may in fact be more consistent with cuspy dark matter distributions than earlier work has claimed.