Searching for Non-axisymmetries in NGC 6503: A Weak End-on Bar

TL;DR

This study introduces DiskFit, a new tool for analyzing non-axisymmetries in galaxy data, applied to NGC 6503, revealing a faint, end-on bar with minimal impact on the galaxy's overall kinematics and structure.

Contribution

The paper presents DiskFit, a novel publicly available code for fitting non-axisymmetries in galaxy kinematic and photometric data, demonstrated on NGC 6503.

Findings

NGC 6503 has regular gas kinematics consistent with pure rotation.

The galaxy hosts a faint, end-on bar contributing about 5% of total light.

A weak bar likely influences the surface brightness profile but not the sigma-drop.

Abstract

The isolation, simple apparent structure, and low luminosity of the nearby spiral galaxy NGC 6503 make it an ideal candidate for an in-depth kinematic and photometric study. We introduce a new publicly available code, DiskFit, that implements procedures for fitting non-axisymmetries in either kinematic or photometric data. We use DiskFit to analyze new Halpha and CO velocity field data as well as HI kinematics from Greisen et al. to search for non-circular motions in the disc of NGC 6503. We find NGC 6503 to have remarkably regular gas kinematics that are well-described by rotation only. We also use DiskFit and a new Ks-band image of NGC 6503 to constrain photometric models of the disc, bar and bulge. We find the galaxy to be photometrically dominated by the disc. We find NGC 6503 to contain a faint bar and an exponential bulge which together contribute only ~5% of the total galaxy light. The combination of our kinematic and photometric DiskFit models suggest that NGC 6503 contains a weak, end-on bar that may have produced its Type II surface brightness profile but is unlikely to be responsible for its strong sigma-drop.