The Galactic Center arms inferred from the ALMA CMZ Exploration Survey (ACES)
Journal article, 2025
Analyzing longitude-velocity diagrams (LVDs) in the CS (J = 2-1) and (HCN)-C-13 (J = 1-0) molecular lines from the internal release data of the ALMA Central Molecular Zone (CMZ) Exploration Survey and in the (CO)-C-13 (J = 1-0) line from the Nobeyama Galactic Center (GC) survey, we identify six GC arms as prominent straight LV ridges. In addition to the currently known Arms I to IV, we identify a new inner arm, Arm V, and further highlight the circumnuclear disk (CND) as Arm VI. Integrated intensity maps of the arms on the sky suggest that most of the arms compose ring-like structures inclined from the Galactic plane. We determine the radii (curvatures) of the arms using the velocity-gradient (dv/dl) method, assuming that the arms are rotating in circular orbits at a constant velocity of similar to 150 km s(-1). We show that Arms I and II compose the main ring structure of the CMZ with radii similar to 100-120 pc; Arm III is a dense arm 42 pc from the GC; Arm IV is a clear and narrow arm 20 pc from the GC; and Arm V is a faint, long arm of 8.2 pc radius. We show that the CND comprises the sixth arm, Arm VI, of radius similar to 2.3 pc associated with bifurcated spiral fins. We also discuss the association of the 20 and 50 km s(-1) clouds with these arms. The radii of the arms fall on an empirical relation R similar to 630 (2/5)(N) for N=1 (Arm I) to 6 (VI), suggesting discrete rings or a logarithmic spiral with pitch angle similar to 22 degrees. The vertical full extent of the arm increases with radius and is represented by z similar to 0.7 (R/1 pc)(0.7) pc. The tilt angle of the arms from the Galactic plane, or the warping, increases rapidly toward the GC.
Galaxy: Center
Galaxy: structure
ISM: clouds
ISM: kinematics and dynamics
ISM: molecules
Author
Yoshiaki Sofue
University of Tokyo
Tomoharu Oka
Keio University
Steven N. Longmore
Liverpool John Moores University
COOL Research DAO
Daniel Walker
University of Manchester
Adam Ginsburg
University of Florida
Jonathan D. Henshaw
Liverpool John Moores University
Max Planck Society
John Bally
University of Colorado
Ashley T. Barnes
European Southern Observatory (ESO)
Cara Battersby
University of Connecticut
Laura Colzi
Spanish National Research Council (CSIC)
Paul Ho
National Taiwan University
Izaskun Jimenez-Serra
Spanish National Research Council (CSIC)
J. M. Diederik Kruijssen
Technical University of Munich
COOL Research DAO
Elizabeth Mills
University of Kansas
Maya Petkova
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Mattia C. Sormani
University of Insubria
University of Surrey
Jen Wallace
University of Connecticut
Jairo Armijos-Abendano
Escuela Politécnica Nacional
Katarzyna M. Dutkowska
Leiden University
Rei Enokiya
Nagoya University
Yasuo Fukui
Nagoya University
Pablo Garcia
Chinese Academy of Sciences
Universidad Catolica del Norte
Andres Guzman
Atacama Large Millimeter-submillimeter Array (ALMA)
Christian Henkel
Max Planck Society
Pei-Ying Hsieh
National Astronomical Observatory of Japan
Yue Hu
Princeton University
Katharina Immer
European Southern Observatory (ESO)
Desmond Jeff
University of Florida
National Radio Astronomy Observatory
Ralf S. Klessen
Heidelberg University
Harvard University
Harvard-Smithsonian Center for Astrophysics
Kotaro Kohno
University of Tokyo
Mark R. Krumholz
Australian National University
Dani Lipman
University of Connecticut
Mark R. Morris
University of California
Francisco Nogueras-Lara
European Southern Observatory (ESO)
M. Nonhebel
European Southern Observatory (ESO)
University of St Andrews
Jurgen Ott
National Radio Astronomy Observatory
Jaime E. Pineda
MPI fur Extraterrestrische Physik
Sergio Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
Miguel Angel Requena-Torres
Towson University
Victor M. Rivilla
Spanish National Research Council (CSIC)
Denise Riquelme-Vasquez
University of La Serena
Alvaro Sanchez-Monge
Inst Estudis Espacials Catalunya IEEC
Spanish National Research Council (CSIC)
Miriam G. Santa-Maria
University of Florida
Howard A. Smith
Harvard-Smithsonian Center for Astrophysics
Tabassum S. Tanvir
Iowa State University
Volker Tolls
Harvard-Smithsonian Center for Astrophysics
Q. Daniel Wang
University of Massachusetts
Publication of the Astronomical Society of Japan
0004-6264 (ISSN) 2053051x (eISSN)
Vol. 77 4 687-706Subject Categories (SSIF 2025)
Fluid Mechanics
Astronomy, Astrophysics, and Cosmology
DOI
10.1093/pasj/psaf034