Milky way mass galaxies with X-shaped bulges are not rare in the local universe

Abstract

Boxy/Peanut/X-shaped (B/P/X) bulges are studied using the 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies, and the Ks-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 ∼50 per cent of bars and axial ratios of ∼0.6-0.9. Based on observations (extending Laurikainen et al.) 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 μm colours of the host galaxies, and the fact that the combined axial ratio distribution of the host galaxy discs 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 multicomponent 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.