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

Herrera-Endoqui, M.; Salo, H.; Laurikainen, E.; Knapen, J. H.
Bibliographical reference

Astronomy & Astrophysics, Volume 599, id.A43, 23 pp.

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Aims: We aim to 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 part of the bar in a similar manner to boxy/peanut bulges in the edge-on view. Methods: A sample of 79 barlens galaxies was selected from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and the Near IR S0 galaxy Survey (NIRS0S), based on previous morphological classifications at 3.6 μm and 2.2 μm wavelengths. For these galaxies the sizes, ellipticities, and orientations of barlenses were measured, parameters which were used to define the barlens regions in the color measurements. In particular, the orientations of barlenses were studied with respect to those of the "thin bars" and the line-of-nodes of the disks. For a subsample of 47 galaxies color index maps were constructed using the Sloan Digital Sky Survey (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 also calculated for each individual galaxy, and presented in histogram form. Results: 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 also similar to those of normal E/S0 galaxies. Galaxy by galaxy studies also 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.
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