On the nature of the barlens component in barred galaxies: what do boxy/peanut bulges look like when viewed face-on?

TL;DR

This study investigates barlenses in barred galaxies, revealing they are the face-on view of the vertically thick part of the bar, which impacts understanding of galactic structure and the prevalence of classical bulges.

Contribution

The paper demonstrates that barlenses are the face-on perspective of boxy/peanut bulges, challenging previous assumptions about classical bulge prevalence in galaxy evolution.

Findings

Barlenses are the face-on view of the thick part of the bar.

Classical bulges are less common and less massive than previously thought.

A new rule of thumb for measuring barlens extent in inclined galaxies.

Abstract

Barred galaxies have interesting morphological features whose presence and properties set constraints on galactic evolution. Here we examine barlenses, i.e. lens-like components whose extent along the bar major axis is shorter than that of the bar and whose outline is oval or circular. We identify and analyse barlenses in $N$-body plus SPH simulations, compare them extensively with those from the NIRS0S (Near-IR S0 galaxy survey) and the S$^4$G samples (Spitzer Survey of Stellar Structure in Galaxies) and find very good agreement. We observe barlenses in our simulations from different viewing angles. This reveals that barlenses are the vertically thick part of the bar seen face-on, i.e. a barlens seen edge-on is a boxy/peanut/X bulge. In morphological studies, and in the absence of kinematics or photometry, a barlens, or part of it, may be mistaken for a classical bulge. Thus the true importance of classical bulges, both in numbers and mass, is smaller than currently assumed, which has implications for galaxy formation studies. Finally, using the shape of the isodensity curves, we propose a rule of thumb for measuring the barlens extent along the bar major axis of moderately inclined galaxies, thus providing an estimate of which part of the bar is thicker.