The pattern speeds of NGC 6946

TL;DR

This paper measures the pattern speeds of NGC 6946's bar and identifies an additional faster pattern, revealing complex dynamical structures through velocity field analysis and resonance calculations.

Contribution

It introduces a novel analysis of multiple pattern speeds in NGC 6946 using the Tremaine-Weinberg method and resonance radius calculations.

Findings

Main pattern speed of 21.7 km/s/kpc with uncertainties

Evidence of an additional faster pattern in the galaxy

Identification of resonance radii indicating evolved bar structures

Abstract

We study the kinematics of the barred spiral galaxy NGC 6946 by investigating the velocity field from H-alpha Fabry-Perot observations, determined the pattern speed of the bar by using the Tremaine-Weinberg method, and find a main pattern speed of 21.7 (+4.0,-0.8) km/s/kpc. Our data clearly suggest the presence of an additional pattern with a pattern speed more than twice that of the large pattern in this galaxy. We use the epicycle approximation to deduce the location of the resonance radii and subsequently determine the pattern speed between the radii, and find that inside the inner Inner Lindblad Resonance radius, a bar-like system has evolved.