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Is the Galactic Spiral Potential 2- or 4-arms?

Published online by Cambridge University Press:  02 August 2018

Preben Grosbøl Open the ORCID record for Preben Grosbøl [Opens in a new window]  and
Giovanni Carraro
Preben Grosbøl
Affiliation:
European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748, Garching, Germany email: pgrosbol@eso.org
Giovanni Carraro
Affiliation:
Dipartimento di Fisica e Astronomia, Universita di Padova Vicolo Osservatorio 3, I-35122, Padova, Italy email: giovanni.carraro@unipd.it
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Abstract

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Young objects (e.g. OB-associations and HII regions) in the Galaxy outline a 4-armed spiral structure whereas the tangent points of arms observed in the near-infrared indicate a 2-armed pattern. The more important issue is whether the spiral potential in the Galaxy is 2- or 4-armed i.e. if all arms traced by young objects also have a significant mass perturbation associated to them. This can be tested by studying the mean radial velocity of a well defined stellar population across the spiral arms and thereby estimating the surface density change.

The current paper presents a preliminary analysis of the radial velocities of a sample of 736 early-type stars toward the Galactic center observed with FLAMES/VLT. A comparison with N-body models in a fixed spiral potential with 2 or 4 arms suggests that no significant mass is associated to the Sagittarius arm. The data are consistent with 2-armed models with pattern speeds in the range of 15-30 km s−1 kpc−1 and relative radial forces of less than 4%.

Keywords

Galaxy: structureGalaxy: kinematics and dynamicsGalaxy: disk
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 13 , Symposium S334: Rediscovering our Galaxy , July 2017 , pp. 300 - 301
Copyright
Copyright © International Astronomical Union 2018 

Footnotes

†

Based on observations collected at the European Southern Observatory, Chile (ESO programme 097.B-00245, 099.B-0697)

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