We compare the observed radial velocity of different arm tracers, taken near the tangent to a spiral arm. A slight difference is predicted by the density wave theory, given the shock predicted at the entrance to the inner spiral arm. In many of these spiral arms, the observed velocity offset confirms the prediction of the density wave theory (with a separation between the maser velocity and the CO gas peak velocity, of about 20 km/s)—when the observed offset is bigger than the error estimates.
Vallée. J.P. (2022) Catalog of Spiral Arm Tangents (Galactic Longitudes) in the Milky Way, and the Age Gradient Based on Various Arm Tracers. New Astronomy, 97, Article ID: 101896. https://doi.org/10.1016/j.newast.2022.101896
Vallée, J.P. (2014) Catalog of Observed Tangents to the Spiral Arms in the Milky Way Galaxy. The Astrophysical Journal Supplement Series, 215, Article No. 1. https://doi.org/10.1088/0067-0049/215/1/1
Vallée, J.P. (2016) A Substructure Inside Spiral Arms, and a Mirror Image Across the Galactic Meridian. The Astrophysical Journal, 821, Article No. 53. https://doi.org/10.3847/0004-637X/821/1/53
Vallée, J.P. (2014) The Spiral Arms of the Milky Way: The Relative Location of Each Different Arm Tracer, within a Typical Spiral Arm Width. The Astronomical Journal, 148, Article No. 5. https://doi.org/10.1088/0004-6256/148/1/5
Vallée, J.P. (2008) New Velocimetry and Revised Cartography of the Spiral Arms in the Milky Way—A Consistent Symbiosis. The Astronomical Journal, 135, 1301-1310. https://doi.org/10.1088/0004-6256/135/4/1301
Vallée, J.P. (2017) A Guided Map to the Spiral Arms in the Galactic Disk of the Milky Way. Astronomical Review, 13, 113-146. https://doi.org/10.1080/21672857.2017.1379459
Vallée, J.P. (2022) The Observed Age Gradient in the Milky Way—As a Test for Theories of Spiral Arm Structure. Astrophysics and Space Science, 367, Article No. 26. https://doi.org/10.1007/s10509-022-04057-2
Abuter, R., Amorim, A., et al. (2019) A Geometric Distance Measurement to the Galactic Center Black Hole with 0.3% Uncertainty. Astronomy & Astrophysics, 625, Article No. L10. https://doi.org/10.1051/0004-6361/201935656
Vallée, J.P. (2017) The Norma Spiral Arm: Large-Scale Pitch Angle. Astrophysics and Space Science, 362, Article No. 173. https://doi.org/10.1007/s10509-017-3145-5
Vallée, J.P. (2015) Different Studies of the Global Pitch Angle of the Milky Way’s Spiral Arms. Monthly Notices of the Royal Astronomical Society, 450, 4277-4284. https://doi.org/10.1093/mnras/stv862
Vallée, J.P. (2016) The Start of the Sagittarius Spiral Arm (Sagittarius Origin) and the Start of the Norma Spiral Arm (Norma Origin): Model-Computed and Observed Arm Tangents at Galactic Longitudes -20 o o . The Astronomical Journal, 151, Article No. 55. https://doi.org/10.3847/0004-6256/151/3/55
Drimmel, R. and Poggio, E. (2018) On the Solar Velocity. Research Notes of the AAS, 2, Article No. 210. https://doi.org/10.3847/2515-5172/aaef8b
Vallée, J.P. (2021) Arm Tangents and the Spiral Structure of the Milky Way—The Age Gradient. International Journal of Astronomy and Astrophysics, 11, 445-457. https://doi.org/10.4236/ijaa.2021.114022
Vallée, J.P. (2022) Superposing the Magnetic Spiral Structure of the Milky Way, on the Stellar Spiral Arms—Matching the Unique Galactic Magnetic Field Reversal Zone with Two Galactic Spiral Arm Segments. International Journal of Astronomy and Astrophysics, 12, 281-300. https://doi.org/10.4236/ijaa.2022.124017
Roberts, W.W. (1969) Large-Scale Shock Formation in Spiral Galaxies and Its Implications on Star Formation. Astrophysical Journal, 158, 123-143. https://doi.org/10.1086/150177
Roberts, W.W. (1975) Theoretical Aspects of Galactic Research. Vistas in Astronomy, 19, 91-109. https://doi.org/10.1016/0083-6656(75)90008-2
Velusamy, T., Langer, W., Pineda, J. and Goldsmith, P. (2012) [C II] 158 μm Line Detection of the Warm Ionized Medium in the Scutum-Crux Spiral Arm Tangency. Astronomy & Astrophysics, 541, Article No. L10. https://doi.org/10.1051/0004-6361/201219303
Velusamy, T., Langer, W.D., Goldsmith, P.F. and Pineda, J.L. (2015) Internal Structure of Spiral Arms Traced with [C II]: Unraveling the Warm Ionized Medium, H I, and Molecular Emission Lanes. Astronomy & Astrophysics, 578, Article No. A135. https://doi.org/10.1051/0004-6361/201525902
Vallée, J.P. (2019) Spatial and Velocity Offsets of Galactic Masers from the Centres of Spiral Arms. Monthly Notices of the Royal Astronomical Society, 489, 2819-2829. https://doi.org/10.1093/mnras/stz2199
Vallée, J.P. (2021) A Low Density Wave’s Spiral Pattern Speed, from the Tracer Separations (Age Gradient) Across a Spiral Arm in the Milky Way. Monthly Notices of the Royal Astronomical Society, 506, 523-530. https://doi.org/10.1093/mnras/stab1679
Gillman, M. (2022) The Galactic Signal of Impact Ages and the Ultimate Causes of the Largest Extinctions. In Press.
Gillman, M.P., Erenier, H.E. and Sutton, P.J. (2019) Mapping the Location of Terrestrial Impacts and Extinctions onto the Spiral Arm Structure of the Milky Way. International Journal of Astrobiology, 18, 323-328. https://doi.org/10.1017/S1473550418000125
Gillman, M. and Erenier, H. (2008) The Galactic Cycle of Extinction. International Journal of Astrobiology, 7, 17-26. https://doi.org/10.1017/S1473550408004047
Kirkland, C., Sutton, P., Johnson, T., et al. (2022) Did Transit through the Galactic Spiral Arms Seed Crust Production on the Early Earth? Geology, 50, 1312-1317. https://doi.org/10.1130/G50513.1
Reid, M.J., Menten, K.M., Brunthaler, A., et al. (2019) Trigonometric Parallaxes of High-Mass Star-Forming Regions: Our View of the Milky Way. The Astrophysical Journal, 885, Article No. 131. https://doi.org/10.3847/1538-4357/ab4a11
Drimmel, R., Romero-Gomez, M., Chemin, L., et al. (2022) Gaia Data Release 3: Mapping the Asymmetric Disc of the Milky Way. ArXiv: 2206.06207.
Vallée, J.P. (2020) Interarm Islands in the Milky Way—The One Near the Cygnus Spiral Arm. Monthly Notices of the Royal Astronomical Society, 494, 1134-1142. https://doi.org/10.1093/mnras/staa758
Vallée, J.P. (2020) A New Multitracer Approach to Defining the Spiral Arm Width in the Milky Way. The Astrophysical Journal, 896, Article No. 19. https://doi.org/10.3847/1538-4357/ab8eab