Milky Way mass galaxies with X-shaped bulges are not rare in the local Universe

TL;DR

This study reveals that Milky Way-mass galaxies with boxy, peanut, or X-shaped bulges are common in the local universe, and these structures are likely the face-on counterparts of barlenses, indicating a prevalence of bulgeless galaxies.

Contribution

The paper provides observational evidence linking B/P/X-shaped bulges and barlenses, and demonstrates that such bulge structures are common in Milky Way-mass galaxies with minimal classical bulges.

Findings

18 new X-shaped structures identified across various inclinations.

Barlenses and X-shapes are likely the same phenomenon viewed from different angles.

Many Milky Way-mass galaxies lack significant classical bulges.

Abstract

Boxy/Peanut/X-shaped (B/P/X) bulges are studied using the 3.6 mum images from the Spitzer Survey of Stellar Structure in Galaxies, and the K_s-band images from the Near-IR S0 galaxy Survey. They are compared with the properties of barlenses, defined as lens-like structures embedded in bars, with sizes of about 50% of bars and axial ratios of 0.6-0.9. Based on observations and recent simulation models we show evidence that barlenses are the more face-on counterparts of B/P/X-shaped bulges. Using unsharp masks 18 new X-shaped structures are identified, covering a large range of galaxy inclinations. The similar masses and red B-3.6 mum colors of the host galaxies, and the fact that the combined axial ratio distribution of the host galaxy disks is flat, support the interpretation that barlenses and X-shapes are physically the same phenomenon. In Hubble types -3<T<2 even half of the bars contain either a barlens or an X-shaped structure. Our detailed 2D multi-component decompositions for 29 galaxies, fitting the barlens/X-shape with a separate component, indicate very small or non-existent classical bulges. Taking into account that the structures we study have similar host galaxy masses as the Milky Way (MW), our results imply that MW mass galaxies with no significant classical bulges are common in the nearby Universe.