The bar and spiral arms in the Milky Way: structure and kinematics

作者：Juntai Shen,Xing-Wu Zheng

摘要：The Milky Way is a spiral galaxy with the Schechter characteristic luminosity L*,thus an important anchor point of the Hubble sequence of all spiral galaxies.Yet the true appearance of the Milky Way has remained elusive for centuries.We review the current best understanding of the structure and kinematics of our home galaxy,and present an updated scientifically accurate visualization of the Milky Way structure with almost all components of the spiral arms,along with the COBE image in the solar perspective.The Milky Way contains a strong bar,four major spiral arms,and an additional arm segment(the Local arm)that may be longer than previously thought.The Galactic boxy bulge that we observe is mostly the peanut-shaped central bar viewed nearly end-on with a bar angle of~25°-30°from the SunGalactic center line.The bar transitions smoothly from a central peanut-shaped structure to an extended thin part that ends around R~5 kpc.The Galactic bulge/bar contains~30%-40%of the total stellar mass in the Galaxy.Dynamical modelling of both the stellar and gas kinematics yields a bar pattern rotation speed of~35-40 km s-1 kpc-1,corresponding to a bar rotation period of~160-180 Myr.From a galaxy formation point of view,our Milky Way is probably a pure-disk galaxy with little room for a significant merger-made,"classical"spheroidal bulge,and we give a number of reasons why this is the case.

發文機構：Department of Astronomy Shanghai Key Laboratory for Particle Physics and Cosmology Department of Astronomy

關鍵詞：Galaxy:structureGalaxy:bulgeGalaxy:kinematicsanddynamicsgalaxies:spiralgalaxies:structure

分類號： P156[天文地球—天文學]