The Properties of the Galactic Bar Implied by Gas Kinematics in the Inner Milky Way
نویسنده
چکیده
Longitude-velocity (l−V ) diagrams of H I and CO gas in the inner Milky Way have long been known to be inconsistent with circular motion in an axisymmetric potential. Several lines of evidence suggest that the Galaxy is barred, and gas flow in a barred potential could be consistent with the observed “forbidden” velocities and other features in the data. We compare the H I observations to l−V diagrams synthesized from 2–D fluid dynamical simulations of gas flows in a family of barred potentials. The gas flow pattern is very sensitive to the parameters of the assumed potential, which allows us to discriminate among models. We present a model that reproduces the outer contour of the H I l−V diagram reasonably well; this model has a strong bar with a semimajor axis of 3.6 kpc, an axis ratio of approximately 3:1, an inner Lindblad resonance (ILR), and a pattern speed of 42 km s kpc, and matches the data best when viewed from 34 to the bar major axis. The behavior of the models, combined with the constraint that the shocks in the Milky Way bar should resemble those in external barred galaxies, leads us to conclude that wide ranges of parameter space are incompatible with the observations. In particular we suggest that the bar must be fairly strong, must have an ILR, and cannot be too end-on, with the bar major axis at 35 ± 5 to the line of sight. The H I data exhibit larger forbidden velocities over a wider longitude range than are seen in molecular gas; this important difference is the reason our favored model differs so significantly from other recently proposed models. Subject headings: Galaxies: Kinematics and Dynamics — Galaxies: The Galaxy — Galaxy: Kinematics and Dynamics — Galaxy: Structure — ISM: Kinematics and Dynamics — Radio lines: ISM
منابع مشابه
3D self-consistent N -body barred models of the Milky Way II. Gas dynamics
The gas dynamics in the Galactic disc is modeled by releasing an initially axisymmetric SPH component in a completely self-consistent and symmetry-free 3D N -body simulation of the Milky Way in which the stellar components display a COBE-like bar. The density centre of the stellar bar wanders around the centre of mass and the resulting gas flow is asymmetric and non-stationary, reproducing the ...
متن کامل3 D self - consistent N - body barred models of the Milky Way
The gas dynamics in the Galactic disc is modeled by releasing an initially axisymmetric SPH component in a completely self-consistent and symmetry-free 3D N-body simulation of the Milky Way in which the stellar components display a COBE-like bar. The density centre of the stellar bar wanders around the centre of mass and the resulting gas flow is asym-metric and non-stationary, reproducing the ...
متن کاملMultiplicity of nuclear dust lanes and dust lane shocks in the Milky Way bar
Aims. We show the existence of a small family of inner-galaxy dust lanes and dust lane standing shocks beyond the two major ones that were previously known to exist Methods. We analyze images of CO emission in the inner regions of the Galaxy Results. The peculiar kinematics of the major dust lane features are repeated in several other distinct instances at l > 0o, in one case at a contrary loca...
متن کاملGas flow models in the Milky Way embedded bars
Context. The gas distribution and dynamics in the inner Galaxy present many unknowns as the origin of the asymmetry of the lv-diagram of the Central Molecular Zone (CMZ). On the other hand, there are recent evidences in the stellar component of the presence of a nuclear bar that could be slightly lopsided. Aims. Our goal is to characterize the nuclear bar observed in 2MASS maps and to study the...
متن کاملAnother Bar in the Bulge
A map of the projected density of the old stellar population of the Galactic Bulge region is reconstructed using 2MASS data. By making a combination of the H and K photometric bands , it is possible to overcome the effect of reddening, and thus penetrate the inner structure of the Galactic Bulge. The main structure in the map corresponds to the well documented peanut shaped bar which is formed ...
متن کامل