title: The local spiral structure of the Milky Way.
abstract: The nature of the spiral structure of the Milky Way has long been debated. Only in the last decade have astronomers been able to accurately measure distances to a substantial number of high-mass star-forming regions, the classic tracers of spiral structure in galaxies. We report distance measurements at radio wavelengths using the Very Long Baseline Array for eight regions of massive star formation near the Local spiral arm of the Milky Way. Combined with previous measurements, these observations reveal that the Local Arm is larger than previously thought, and both its pitch angle and star formation rate are comparable to those of the Galaxy's major spiral arms, such as Sagittarius and Perseus. Toward the constellation Cygnus, sources in the Local Arm extend for a great distance along our line of sight and roughly along the solar orbit. Because of this orientation, these sources cluster both on the sky and in velocity to form the complex and long enigmatic Cygnus X region. We also identify a spur that branches between the Local and Sagittarius spiral arms.
authors.affiliation: Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China.
authors.forename: Ye
authors.initials: Y
authors.lastname: Xu
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Reid
authors.affiliation: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Dame
authors.affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
authors.forename: Karl
authors.identifier: 0000-0001-6459-0669
authors.initials: K
authors.lastname: Menten
authors.affiliation: Mizusawa VLBI (Very Long Baseline Interferometry) Observatory, National Astronomical Observatory of Japan, Japan.
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Sakai
authors.affiliation: Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China.; Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
authors.forename: Jingjing
authors.initials: J
authors.lastname: Li
authors.affiliation: Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany.
authors.forename: Andreas
authors.identifier: 0000-0003-4468-761X
authors.initials: A
authors.lastname: Brunthaler
authors.affiliation: INAF (Istituto Nazionale di Astrofisica)-Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Moscadelli
authors.affiliation: Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China.
authors.forename: Bo
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Nanjing University, Nanjing 210093, China.
authors.forename: Xingwu
authors.initials: X
authors.lastname: Zheng
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D018534:Earth, Planet; D006801:Humans; D013057:Spectrum Analysis; D055609:Stars, Celestial
keywords: Masers; astrometry; galaxy spiral arm; high angular resolution; star formation