An Eclectic View of our Milky Way Galaxy

Abstract

The nature of our Milky Way Galaxy is reexamined from an eclectic point of view. Evidence for a central bar, for example, is not reflected in the distribution of RR Lyrae variables in the central bulge [4,5], and it is not clear if either a 2-armed or 4-armed spiral pattern is appropriate for the spiral arms. Radial velocity mapping of the Galaxy using radio H I, H II, or CO observations is compromised by the assumptions adopted for simple Galactic rotation. The Sun's local standard of rest (LSR) velocity is $\sim 14$ km s${}^{-1}$ rather than 20 km s${}^{-1}$, the local circular velocity is $251\pm 9$ km s${}^{-1}$ rather than 220 km s${}^{-1}$, and young groups of stars exhibit a 10--20 km s${}^{-1}$ "kick" relative to what is expected from Galactic rotation. By implication, the same may be true for star-forming gas clouds affected by the Galaxy's spiral density wave, raising concerns about their use for mapping spiral arms. Proper motion data in conjunction with the newly-estimated velocity components for the Sun's motion imply a distance to the Galactic centre of $R_0=8.34\pm 0.27$ kpc, consistent with recent estimates which average $8.24\pm 0.09$ kpc. A cosinusoidal Galactic potential is not ruled out by observations of open star clusters. The planetary nebula cluster Bica 6, for example, has a near-escape orbit for a Newtonian potential, but a near-normal orbit in a cosinusoidal potential field. The nearby cluster Collinder 464 also displays unusually large tidal effects consistent with those expected for a cosinusoidal potential. A standard Newtonian version of the Virial Theorem for star clusters yields very reasonable masses ($\sim 3\times 10^{11}{M}_{\odot }$ and $\sim 4\times 10^{11}{M}_{\odot }$) for the Milky Way and M31 subgroups of the Local Group, respectively. A cosinusoidal relation should yield identical results.

To appear in the CJP

References in corpus (4)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• The Vertical Structure of the Outer Milky Way HI Disk
• The Spiral Structure of the Outer Milky Way in Hydrogen
• The distance to the young open cluster Westerlund 2

Cited by in corpus (4)

• Cepheid Abundances: Multiphase Results and Spatial Gradients
• Establishing the Galactic Centre Distance Using VVV Bulge RR Lyrae Variables
• Extinction in the Star Cluster SAI~113 and Galactic Structure in Carina
• Topography of the Young Galactic Disk: Spatial and Kinematic Patterns of the Clustered Star Formation in the Solar Neighborhood