The Galactic Center arms inferred from the ALMA CMZ Exploration Survey (ACES)

Abstract Analyzing longitude–velocity diagrams (LVDs) in the CS (J = 2–1) and H$^{13}$CN (J = 1–0) molecular lines from the internal release data of the ALMA Central Molecular Zone (CMZ) Exploration Survey and in the $^{13}$CO (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 $\sim$150 km s$^{-1}$. We show that Arms I and II compose the main ring structure of the CMZ with radii $\sim$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 $\sim$2.3 pc associated with bifurcated spiral fins. We also discuss the association of the 20 and 50 km s$^{-1}$ clouds with these arms. The radii of the arms fall on an empirical relation $R\sim 630 (2/5)^N$ for $N=1$ (Arm I) to 6 (VI), suggesting discrete rings or a logarithmic spiral with pitch angle ${\sim }22^{\circ }$. The vertical full extent of the arm increases with radius and is represented by $z\sim 0.7 (R/1 {\rm \ pc} )^{0.7}$ pc. The tilt angle of the arms from the Galactic plane, or the warping, increases rapidly toward the GC.

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Journal
Publications of the Astronomical Society of Japan
Published
2025-06-11
DOI
https://doi.org/10.1093/pasj/psaf034
Primary Topic
Astrophysics and Star Formation Studies
Type
article
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0.00

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article

The Galactic Center arms inferred from the ALMA CMZ Exploration Survey (ACES)

Volker Tolls, Andrés E. Guzmán, J. Ott, Jairo Armijos-Abendaño et al.
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Publications of the Astronomical Society of Japan
Astrophysics and Star Formation Studies
article

The Galactic Center arms inferred from the ALMA CMZ Exploration Survey (ACES)

Volker Tolls, Andrés E. Guzmán, J. Ott, Jairo Armijos-Abendaño, Laura Colzi, Mark R. Krumholz, Yue Hu, Paul T. P. Ho, J. E. Pineda, F. Nogueras-Lara, Maya A. Petkova, V. M. Rivilla, Miriam G. Santa-Maria, K. M. Dutkowska, J. M. Diederik Kruijssen, Ashley T. Barnes, Pei‐Ying Hsieh, John Bally, Á. Sánchez-Monge, Tabassum S Tanvir, Desmond Jeff, Jonathan D. Henshaw, Daniel L. Walker, J. Kent Wallace, S. Martín, Tomoharu Oka, Cara Battersby, Mattia C. Sormani, K. Immer, Ralf S. Klessen, Q. Daniel Wang, Steven N. Longmore, Elizabeth Mills, Y. Fukui, Pablo García, C. Henkel, Dani Lipman, Kotaro Kohno, Izaskun Jiménez-Serra, Yoshiaki Sofue, Rei Enokiya, Adam Ginsburg, M. Nonhebel, Miguel A. Requena-Torres, H. A. Smith, Mark R. Morris, Denise Riquelme-Vásquez
article en

Abstract

Abstract Analyzing longitude–velocity diagrams (LVDs) in the CS (J = 2–1) and H$^{13}$CN (J = 1–0) molecular lines from the internal release data of the ALMA Central Molecular Zone (CMZ) Exploration Survey and in the $^{13}$CO (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 $\sim$150 km s$^{-1}$. We show that Arms I and II compose the main ring structure of the CMZ with radii $\sim$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 $\sim$2.3 pc associated with bifurcated spiral fins. We also discuss the association of the 20 and 50 km s$^{-1}$ clouds with these arms. The radii of the arms fall on an empirical relation $R\sim 630 (2/5)^N$ for $N=1$ (Arm I) to 6 (VI), suggesting discrete rings or a logarithmic spiral with pitch angle ${\sim }22^{\circ }$. The vertical full extent of the arm increases with radius and is represented by $z\sim 0.7 (R/1 {\rm \ pc} )^{0.7}$ pc. The tilt angle of the arms from the Galactic plane, or the warping, increases rapidly toward the GC.

Publications of the Astronomical Society of Japan
University of Insubria (IT), Australian National University (AU), Leiden University (NL), Institute of Astronomy and Astrophysics, Academia Sinica (TW), European Southern Observatory (DE), Institute of Space Sciences (ES), Harvard University (US), University of Connecticut (US), University of Kansas (US), University of California, Los Angeles (US), University of St Andrews (GB), Iowa State University (US), University of Colorado Boulder (US), Keio University (JP), Heidelberg University (DE), University of Massachusetts Amherst (US), National Radio Astronomy Observatory (US), Atacama Large Millimeter Submillimeter Array (CL), Theodore Roosevelt High School (US), Universidad Católica del Norte (CL), University of Surrey (GB), University of Manchester (GB), University of Florida (US), Institute for Advanced Study (US), Max Planck Institute for Extraterrestrial Physics (DE), Institut d'Estudis Espacials de Catalunya (ES), Cool Energy (United States) (US), Max Planck Institute for Astronomy (DE), Laboratory for Atmospheric and Space Physics (US), Institute of Astronomy (RU), Center for Astrophysics Harvard & Smithsonian (US), National Observatory (BR), Centro de Astrobiología (ES), European Southern Observatory (CL), Max Planck Institute for Behavioral Economics (DE), National Astronomical Observatory of Japan (JP), National Astronomical Observatories (CN), Towson University (US), Nagoya University (JP), Technical University of Munich (DE), Liverpool John Moores University (GB), Chalmers University of Technology (SE), National Polytechnic School (EC), The University of Tokyo (JP), University of La Serena (CL)
National Science Foundation, National Aeronautics and Space Administration, U.S. Nuclear Regulatory Commission, European School of Oncology, Korea Astronomy and Space Science Institute, National Astronomical Observatory of Japan, Japan Society for the Promotion of Science, National Institutes of Natural Sciences, H2020 European Research Council
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Astrophysics and Star Formation Studies
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