Bar Classification based on the Potential Map

TL;DR

This paper presents a novel method for classifying barred galaxies using the transverse-to-radial force ratio map in polar coordinates, achieving high accuracy and providing insights into bar properties and evolutionary stages.

Contribution

The study introduces a new classification technique based on the ratio map in polar coordinates, enabling accurate identification of barred galaxies and measurement of bar features separated from spiral arms.

Findings

Achieved 87% classification accuracy for barred vs. nonbarred galaxies.

Found a bar fraction of 53% in nearby spiral galaxies from SDSS/DR7.

Identified two types of radial force ratio profiles, indicating different evolutionary stages.

Abstract

We introduce a new approach to classify barred galaxies that utilizes the transverse-to-radial force ratio map (ratio map, hereafter) in a different manner from previous studies. When we display the ratio map in polar coordinates, barred galaxies appear as four aligned, horizontal thick slabs. This characteristic feature enables us to successfully classify barred and nonbarred galaxies with an accuracy of 87%. It yields the bar fraction of 53%, including both SBs and SABs, when applied to 884 nearby (z < 0.01) spiral galaxies from the Sloan Digital Sky Survey/DR7. It also provides the bar strength and length measurements, in particular, separated from the spiral arms. They show good correlations with the measures estimated from ellipse fitting and Fourier analysis. However, we find different tendencies of the bar strength measurements in terms of the Hubble sequence: as the Hubble sequence increases (towards late-type), the bar strength and bar ellipticity increase, whereas the dipole Fourier amplitude decreases. We show that the bulge affects the estimation of the bar strength differently, depending on the classification methods. The bulge causes the bar length to be overestimated in all three methods. Meanwhile, we find that barred galaxies show two types of radial profiles of the angle-averaged force ratio: one has a maximum peak (type M) and the other a plateau (type P). Comparison with numerical simulations suggests that type M bars are more mature than type P bars in terms of evolutionary stage.