Constraining the NFW Potential with Observations and Modeling of LSB Galaxy Velocity Fields

TL;DR

This study tests whether NFW dark matter halos can explain the observed velocity fields of LSB galaxies, finding that standard NFW models struggle to match the slow rise of their rotation curves unless viewed from specific angles.

Contribution

The paper demonstrates that NFW potentials, both axisymmetric and non-axisymmetric, cannot fully reproduce LSB galaxy rotation curves, highlighting limitations in the NFW model for these galaxies.

Findings

DensePak IFU accurately reconstructs NFW velocity fields.

Non-axisymmetric potentials only alter velocity normalization, not shape.

Matching observed rotation curves requires specific viewing angles, inconsistent with random orientations.

Abstract

We model the NFW potential to determine if, and under what conditions, the NFW halo appears consistent with the observed velocity fields of low surface brightness (LSB) galaxies. We present mock DensePak IFU velocity fields and rotation curves of axisymmetric and non-axisymmetric potentials that are well-matched to the spatial resolution and velocity range of our sample galaxies. We find that the DensePak IFU can accurately reconstruct the velocity field produced by an axisymmetric NFW potential and that a tilted-ring fitting program can successfully recover the corresponding NFW rotation curve. We also find that non-axisymmetric potentials with fixed axis ratios change only the normalization of the mock velocity fields and rotation curves and not their shape. The shape of the modeled NFW rotation curves does not reproduce the data: these potentials are unable to simultaneously bring the mock data at both small and large radii into agreement with observations. Indeed, to match the slow rise of LSB galaxy rotation curves, a specific viewing angle of the non-axisymmetric potential is required. For each of the simulated LSB galaxies, the observer's line-of-sight must be along the minor axis of the potential, an arrangement which is inconsistent with a random distribution of halo orientations on the sky.