Boxy/Peanut/X-shaped Bulges: Steep Inner Rotation Curve Leads to Barlens Face-on Morphology

Abstract

We use stellar dynamical bulge/disk/halo simulations to study whether barlenses (lens-like structures embedded in the narrow bar component) are only the face-on counterparts of Boxy/Peanut/X-shapes (B/P/X) seen in edge-on bars, or if some additional physical parameter affects that morphology. A range of bulge-to-disk mass and size ratios are explored: our nominal parameters (, disk comprisingtwo-thirds of total force at h 2.2 r ) correspond to typical Milky Way mass galaxies. In all models, a bar with pronounced B/P/X forms in a few Gyr, visiblein the edge-on view. However, the pure barlens morphology forms only in models with sufficiently steep inner rotation curves,, achieved when including a small classical bulge with  B D 0.02 and  r h 0.1 r eff . For shallower slopes, the central structure still resembles a barlens, but shows a clear X signature even in low inclinations. A similar result holds for bulge-less simulations, where the central slope is modified by changing the halo concentration. The predicted sensitivity on the inner rotation curve is consistent with the slopes that are estimated from gravitational potentials calculated from the 3.6 μm images, for the observed barlens and X-shaped galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S 4 G). For inclinations <60°t he galaxies with barlenses have on average twice steeper inner rotation curves than galaxies with X shapes: the limiting slope is ∼250 km s −1 kpc −1 . Among barred galaxies, those with barlenses have both the strongest bars and the largest relative excess of inner surface density, both in barlens regions ( h 0.5 r ) and near the center ( h 0.1 r ); this provides evidence for bar-driven secular evolution in galaxies.

The Systematics of Galaxy Morphology in the Comprehensive de Vaucouleurs revised Hubble-Sandage Classification System: Application to the EFIGI Sample

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The shapes of spiral arms in the S4G survey and their connection with stellar bars

“…Davis et al 2017): this could be explained by their use of smaller samples, but we note the lack of clear correlation can be due to the uncertainty in |φ| or to the use of indirect estimates of M BH . 2016b; Salo & Laurikainen 2017). We show that the pitch angle of the galaxy is not dependent on d R v * (0) (right panel of Fig.…”

The kinematics of local thick discs do not support an accretion origin

“…Figure 6 displays a simulation model with superposed thin-and thick-disc components, with equal masses and with scale heights differing by a factor of three. As in Salo & Laurikainen (2017), the initial values have been constructed with the GalactICS software (Kuijken & Dubinski 1995). This code was used to create two separate, self-consistent axisymmetric bulge-disc-halo models, with similar disc-to-total mass ratio and total rotation curve but different vertical thickness of the disc.…”