The observed spiral structure of the Milky Way

By L. Hou, Jin Han. 2014

193 citations recorded by the source corpus.

Context. The spiral structure of the Milky Way is not yet well determined. The keys to understanding this structure are to increase the number of reliable spiral tracers and to determine their distances as accurately as possible. HII regions, giant mol ecular clouds (GMCs), and 6.7-GHz methanol masers are closely related to high mass star formation, and hence they are excellent spiral tracers. The distances for many of them have been determined in literature with trigonometric, photometric and/or kinematic methods. Aims. We update the catalogs of Galactic HII regions, GMCs, and 6.7-GHz methanol masers, and then outline the spiral structure of the Milky Way. Methods. We collected data for more than 2500 known HII regions, 1300 GMCs, and 900 6.7-GHz methanol masers. If the photometric or trigonometric distance was not yet available, we determined the kinematic distance using a Galaxy rotation curve with the current IAU standard, R0 = 8.5 kpc and �0 = 220 km s −1 , and the most recent updated values of R0 = 8.3 kpc and �0 = 239 km s −1 , after we modified the velocities of tracers with the adopted s olar motions. With the weight factors based on the excitation parameters of HII regions or the masses of GMCs, we get the distributions of these spiral tracers. Results. The distribution of tracers shows at least four segments of arms in the first Galactic quadrant, and three segments in the f ourth quadrant. The Perseus Arm and the Local Arm are also delineated by many bright HII regions. The arm segments traced by massive star forming regions and GMCs are able to match the HI arms in the outer Galaxy. We found that the models of three-arm and fourarm logarithmic spirals are able to connect most spiral tracers. The four-arm model provides a better match to the observed tangential directions of spiral arms, and is consistent with the two-fo ld symmetry of the Galaxy structure. A model of polynomial-logarithmic spirals not only delineates the tracer distribution but als o matches the observed tangential directions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f77e6b4225ed981d66c39155a6bde08e0dd2c982

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In Astronomy and Astrophysics

Citations in the corpus

A NEW ELECTRON-DENSITY MODEL FOR ESTIMATION OF PULSAR AND FRB DISTANCES (2016, methodology): “…the Galaxy around 4 kpc Galactocentric radius, spiral arms following a logarithmic-spiral pattern based on the Galactic distribution of H II regions (Hou & Han 2014), a Galactic Center disk of radius 160 pc and scale height 35 pc, an ellipsoidal shell with major axis in the z direction…”
Painting a portrait of the Galactic disc with its stellar clusters (2020, methodology): “A1, page 11 of 17 The presence of young clusters in the region between the Perseus and outer arms can also be interpreted as the trace of interam spurs, as reported by Molina Lera et al. (2019) and suggested by the HII maps of Hou & Han (2014).”
Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc (2019, methodology): “Additional HII regions compiled by Hou & Han (2014) and that correspond to various transitions of H, He, CS, CO and more recent observations (see references in Hou & Han (2014)) are also represented.”
A 3D Dust Map Based on Gaia, Pan-STARRS 1, and 2MASS (2019, background): “…of the Milky Way have been proposed, with between two and four arms (Georgelin & Georgelin 1976; Drimmel 2000; Vallée 2008; Reid et al. 2009; Hou & Han 2014), and with or without a “molecular ring” at 4 kpc from the Galactic center (Stecker et al. 1975; Cohen & Thaddeus 1977; Dobbs &…”
RINGS AND RADIAL WAVES IN THE DISK OF THE MILKY WAY (2015, methodology): “Maps by Hou & Han (2014) suggest that the Perseus Arm is more obvious below the plane, while the north near structure shows more stars above the plane.”