Mapping the dark matter halo of early-type galaxy NGC 2974 through orbit-based models with combined stellar and cold gas kinematics

TL;DR

This paper introduces an orbit-based method combining stellar and cold gas kinematics to better constrain the dark matter profile of early-type galaxy NGC 2974, significantly improving the confidence in dark matter properties.

Contribution

The study develops and applies a novel orbit-based modeling technique that integrates stellar and cold gas kinematics to refine dark matter halo measurements in early-type galaxies.

Findings

Cold gas kinematics significantly tighten dark matter model constraints.

Inclusion of cold gas reduces dark matter fraction uncertainty to 10%.

Measured a shallow inner slope of 0.6 for the dark matter profile.

Abstract

We present an orbit-based method of combining stellar and cold gas kinematics to constrain the dark matter profile of early-type galaxies. We apply this method to early-type galaxy NGC 2974, using Pan-STARRS imaging and SAURON stellar kinematics to model the stellar orbits, and introducing HI kinematics from VLA observation as a tracer of the gravitational potential. The introduction of the cold gas kinematics shows a significant effect on the confidence limits of especially the dark halo properties: we exclude more than $95\%$ of models within the $1-\sigma$ confidence level of Schwarzschild modelling with only stellar kinematics, and reduce the relative uncertainty of the dark matter fraction significantly to $10\%$ within $5 R_\mathrm{e}$. Adopting a generalized-NFW dark matter profile, we measure a shallow cuspy inner slope of $0.6^{+0.2}_{-0.3}$ when including the cold gas kinematics in our model. We cannot constrain the inner slope with the stellar kinematics alone.