Orthogonal vertical velocity dispersion distributions produced by bars

Abstract

In barred galaxies, the contours of stellar velocity dispersions ($\sigma$) are generally expected to be oval and aligned with the orientation of bars. However, many double-barred (S2B) galaxies exhibit distinct $\sigma$ peaks on the minor axis of inner bars, which we termed "$\sigma$-humps," while two local $\sigma$ minima are present close to the ends of inner bars, i.e., "$\sigma$-hollows." Analysis of numerical simulations shows that ${\sigma }_z$-humps or hollows should play an important role in generating the observed $\sigma$-humps+hollows in low-inclination galaxies. In order to systematically investigate the properties of ${\sigma }_z$ in barred galaxies, we apply the vertical Jeans equation to a group of well-designed three-dimensional bar+disk(+bulge) models. A vertically thin bar can lower ${\sigma }_z$ along the bar and enhance it perpendicular to the bar, thus generating ${\sigma }_z$-humps+hollows. Such a result suggests that ${\sigma }_z$-humps+hollows can be generated by the purely dynamical response of stars in the presence of a, sufficiently massive, vertically thin bar, even without an outer bar. Using self-consistent $N$-body simulations, we verify the existence of vertically thin bars in the nuclear-barred and S2B models which generate prominent $\sigma$-humps+hollows. Thus the ubiquitous presence of $\sigma$-humps+hollows in S2Bs implies that inner bars are vertically thin. The addition of a bulge makes the ${\sigma }_z$-humps more ambiguous and thus tends to somewhat hide the ${\sigma }_z$-humps+hollows. We show that ${\sigma }_z$ may be used as a kinematic diagnostic of stellar components that have different thickness, providing a direct perspective on the morphology and thickness of nearly face-on bars and bulges with integral field unit spectroscopy.

14 pages, 16 figures. Accepted for publication in ApJ

References in corpus (16)

• Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory
• The SAURON project -- X. The orbital anisotropy of elliptical and lenticular galaxies: revisiting the (V/sigma,epsilon) diagram with integral-field stellar kinematics
• Dynamics of Barred Galaxies
• A Near-Infrared Study of 2MASS Bars in Local Galaxies: An Anchor for High Redshift Studies
• Calibrating Gyrochronology using Kepler Asteroseismic targets
• The interplay between a galactic bar and a supermassive black hole: nuclear fueling in a sub-parsec resolution galaxy simulation
• The Catalog of Edge-on Disk Galaxies from SDSS. Part I: the catalog and the Structural Parameters of Stellar Disks
• 2D kinematic signatures of boxy/peanut bulges
• Orbital structure in barred spiral galaxies
• Evidence of Bar-induced Secular Evolution in the Inner Regions of Stellar Discs in Galaxies: What Shapes Disc Galaxies?
• Scalelength of disc galaxies
• Stellar kinematics in double-barred galaxies: the sigma-hollows
• Forming Double-barred Galaxies From Dynamically Cool Inner Disks
• GALAXY package for N-body simulation
• Parallel FFT-based Poisson Solver for Isolated Three-dimensional Systems
• Kinematic properties of double-barred galaxies: simulations vs. integral-field observations

Cited by in corpus (2)

• Clocking the assembly of double-barred galaxies with the MUSE TIMER project
• A New Channel of Bulge Formation via The Destruction of Short Bars