Colors of barlenses: evidence for connecting them to boxy/peanut bulges

TL;DR

This study investigates the colors and orientations of barlenses in barred galaxies, providing evidence that they are part of the bar structure and related to boxy/peanut bulges, with implications for galaxy morphology and evolution.

Contribution

It offers the first detailed analysis linking barlenses to bar structures and boxy/peanut bulges through color and orientation measurements in a sizable galaxy sample.

Findings

Barlenses have colors similar to bars, suggesting they are part of the bar.

Barlenses are oriented closer to the disk line-of-nodes, consistent with being vertically thick structures.

Galaxy centers are generally redder, with some showing signs of recent star formation.

Abstract

We study the colors and orientations of structures in low and intermediate inclination barred galaxies. We test the hypothesis that barlenses, roundish central components embedded in bars, could form a part of the bar in a similar manner to boxy/peanut bulges in the edge-on view. A sample of 79 barlens galaxies was selected from the S$^4$G and the NIRS0S surveys. The sizes, ellipticities, and orientations of barlenses were measured and used to define the barlens regions in the color measurements. The orientations of barlenses were studied with respect to those of the "thin bars" and the line-of-nodes of the disks. For 47 galaxies color maps were constructed using the SDSS images in five optical bands, u, g, r, i, and z. Colors of bars, barlenses, disks, and central regions of the galaxies were measured using two different approaches and color-color diagrams sensitive to metallicity, stellar surface gravity, and short lived stars were constructed. Color differences between the structure components were calculated for each individual galaxy, and presented in histogram form. We find that the colors of barlenses are very similar to those of the surrounding bars, indicating that most probably they form part of the bar. We also find that barlenses have orientations closer to the disk line-of-nodes than to the thin bars, which is consistent with the idea that they are vertically thick, in a similar manner as the boxy/peanut structures in more inclined galaxies. Typically, the colors of barlenses are similar to those of normal E/S0 galaxies. Galaxy by galaxy studies show that in spiral galaxies very dusty barlenses also exist, along with barlenses with rejuvenated stellar populations. The central regions of galaxies are found to be on average redder than bars or barlenses, although galaxies with bluer central peaks also exist.