Direct Determination of the Spiral Pattern Rotation Speed of the Galaxy

By W. Dias, J. Lépine. 2005

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The rotation velocity of the spiral pattern of the Galaxy is determined by direct observation of the birthplaces of open clusters of stars in the Galactic disk as a function of their age. Our measurement does not depend on any specific model of the spiral structure, such as the existence of a given number of spiral arms, or the presence of a bar in the central regions. This study became possible due to the recent completion of a large database on open clusters by our group. The birthplaces of the clusters are determined by two methods: one that assumes that the orbits are circular, and the other by integrating the orbits in the Galactic potential for a time equal to the age of the clusters. We selected in the database a sample of 212 clusters for which proper motions, radial velocities, distances, and ages are available, or of 612 clusters that have ages and distances available. We tested different assumptions concerning the rotation curve and the radius R0 of the solar orbit. Our results confirm that a dominant fraction of the open clusters are formed in spiral arms, and that the spiral arms rotate like a rigid body, as predicted by the classical theory of spiral waves. We find that the corotation radius, Rc, is close to the solar Galactic orbit (Rc/R0 = 1.06 ± 0.08). This proximity has many potentially interesting consequences, such as a better preservation of life on the Earth and a new understanding of the history of star formation in the solar neighborhood, and of the evolution of the abundance of elements in the Galactic disk.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/585b4162825b4e6f8c6d3cdb2a212096b0aba6d1

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Citations in the corpus

• Painting a portrait of the Galactic disc with its stellar clusters (2020, background): “The spatial distribution of young clusters is known to correlate with the location of the spiral arms in the Milky Way (Morgan et al. 1953; Becker & Fenkart 1970; Dias & Lépine 2005).”
• A Gaia DR2 view of the open cluster population in the Milky Way (2018, methodology): “…MWSC as a colour-code visually confirms that the youngest clusters are clearly associated with the spiral arms, while older clusters are distributed in a more dispersed fashion, which is naturally explained by the fact that spiral arms are the locus of star formation (see e.g. Dias & Lépine 2005).”
• On the mass-to-light ratio of the local Galactic disc and the optical luminosity of the Galaxy (2006, background): “Although estimates of the local circular velocity down to 185 km s−1 can be found (e.g. Olling & Merrifield 1998; Dias & Lépine 2005), they are at the lowermost end of the plausible range (Sackett 1997; Majewski et al. 2006; and references therein) and seem to be excluded by recent studies of the…”