First direct identification of the barlens vertical structure in galaxy models

TL;DR

This study uses spectral dynamics to dissect a galaxy model with a barlens, revealing distinct components and clarifying the vertical structure and shape of barlenses and their relation to boxy/peanut bulges.

Contribution

It provides the first direct identification of the barlens vertical structure and its components in galaxy models, clarifying their relation to B/P bulges and galaxy morphology.

Findings

Barlens comprises multiple components with distinct orbital support.

The peanut shape mainly results from orbits forming the face-on bar's boxy part.

Rounded face-on barlenses are flat vertically and not fully part of the B/P bulge.

Abstract

Applying spectral dynamics methods to one typical $N$-body model with a barlens, we dissect the modelled bar into separate components supported by completely different types of orbits. We identify at least four components: a narrow elongated bar, a boxy bar, and two components contributing to the barlens. We analyse the vertical structure of all components that make up the thick part of the bar, which has a boxy/peanut shape (B/P bulge). We show that the `peanut' shape is mainly due to the orbits that assemble the boxy part of the face-on bar. We associate the X-shape with the narrow and elongated bar. The wider part of the barlens with square-like isophotes contributes to the boxy shape of the B/P bulge when we observe the galaxy edge-on. However, the part of the barlens with rounded isophotes in the face-on view is a rather flat structure in the vertical direction without any significant off-centre protrusions. Thus, for the first time, we demonstrate that the rounded face-on barlens cannot be entirely associated with the B/P bulge.