Influence of barlens on the bulge parameters in 2D image decomposition

¹ Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
² State Key Laboratory of Dark Matter Physics, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
³ Department of Astronomy, University of Illinois Urbana-Champaign, Urbana, 61801 IL, USA

^⋆ Corresponding authors: lizy.astro@sjtu.edu.cn; yanglianpin@sjtu.edu.cn

Received: 10 March 2025
Accepted: 13 August 2025

Abstract

Context. Recent observations and simulations have shown that a buckled bar in the face-on view can be considered as a combination of a long flat bar and a short, round barlens (corresponding to the boxy/peanut bulge in the edge-on view). However, the barlens component can be misidentified as the bulge, potentially leading to inaccurate bulge parameter measurements in two-dimensional image decomposition.

Aims. Our goal is to explore the optimal method for modeling the barlens component and to understand its impact on bulge parameter measurements in 2D image decomposition.

Methods. We first analyzed mock images from two different simulations (with and without bulge) to verify our decomposition method. We then applied the method to two nearby barred galaxies, NGC 1533 and NGC 7329, from the Carnegie-Irvine Galaxy Survey (CGS). Using GALFIT, we performed 2D image decomposition by gradually increasing the complexity of model configurations. We also explored the effects of inclination by projecting the simulated galaxy to various viewing angles and analyzing the variations in the bulge and barlens parameters.

Results. From the mock images, we find that the bulge-to-total ratio (B/T) could be overestimated by 50% without considering the barlens component; the Sérsic index and effective radius of the bulge are also affected to varying degrees. The decomposition results of the two CGS galaxies are consistent with our mock image tests. Uncertainties of the structural parameters of the bulge and barlens are larger at higher inclination angels due to the strong projection effect in the central region.

Conclusions. Our findings underscore the necessity of accurately modeling the barlens, revealing that its inclusion in 2D image decomposition can lead to a decrease in B/T by ∼30–50%, with other bulge parameters, such as the Sérsic index and effective radius, also affected.