The Galaxy in Context: Structural, Kinematic & Integrated Properties

The Galaxy in Context: Structural, Kinematic & Integrated Properties

2016 | Joss Bland-Hawthorn, Ortwin Gerhard
The Milky Way is a key benchmark for understanding disk galaxies, offering a unique opportunity to study its formation history through the distribution of stars from dwarfs to supergiants. It is a barred spiral galaxy with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. The Galaxy lies in the "green valley" of the galaxy colour-magnitude diagram, indicating a transition between the "red sequence" and the "blue cloud." This review discusses the key integrated, structural, and kinematic parameters of the Galaxy, highlighting uncertainties and future directions. Galactic studies remain crucial for understanding universal processes, as many observations can only be made in the near field. The Galaxy's virial mass and radius have grown over time, with the virial radius marking the extent of stabilization. The NFW concentration parameter c evolves with halo mass, reflecting the Galaxy's dark matter distribution. The Galaxy's formation involved hierarchical accretion, with different components forming at various stages. The central regions formed early, while the outer halo accreted material over time. The thin disk reflects a different accretion process. Recent surveys have cataloged billions of stars with accurate photometric data, but only a fraction have high-quality spectral data. The ESA GAIA mission will provide accurate distances and velocity vectors for millions of stars, aiding future studies. The Galaxy's complexity is challenging to describe, but its components exhibit strong overlap due to shared gravitational potential. Separating components like the bar/bulge from the inner disk and halo remains a challenge, with some arguing for a gradual transition or distinct origins for the thick and thin disks. The Galaxy's structural and kinematic parameters are crucial for comparison with other galaxies and numerical simulations. The Galaxy's distance to the center, R₀, is a key parameter, with recent estimates around 8.2 kpc. The Galaxy's position in the Tully-Fisher relation is consistent with its high circular velocity. The Galaxy's center, Sgr A*, is a supermassive black hole, with recent estimates of its mass around 4.2 million solar masses. The Galaxy's solar offset and Galactic plane are also important, with the true plane slightly inclined relative to the b=0 plane. The Galaxy's disk is nearly flat, with the long bar consistent with a tilted midplane passing through Sgr A* and the point 25 pc below the Sun. The Galaxy's black hole and solar angular velocity are well-measured, with the black hole mass consistent with other estimates. The Galaxy's future evolution and interactions with other galaxies will continue to be studied, providing insights into its dynamic history.The Milky Way is a key benchmark for understanding disk galaxies, offering a unique opportunity to study its formation history through the distribution of stars from dwarfs to supergiants. It is a barred spiral galaxy with a central box/peanut bulge, a dominant disk, and a diffuse stellar halo. The Galaxy lies in the "green valley" of the galaxy colour-magnitude diagram, indicating a transition between the "red sequence" and the "blue cloud." This review discusses the key integrated, structural, and kinematic parameters of the Galaxy, highlighting uncertainties and future directions. Galactic studies remain crucial for understanding universal processes, as many observations can only be made in the near field. The Galaxy's virial mass and radius have grown over time, with the virial radius marking the extent of stabilization. The NFW concentration parameter c evolves with halo mass, reflecting the Galaxy's dark matter distribution. The Galaxy's formation involved hierarchical accretion, with different components forming at various stages. The central regions formed early, while the outer halo accreted material over time. The thin disk reflects a different accretion process. Recent surveys have cataloged billions of stars with accurate photometric data, but only a fraction have high-quality spectral data. The ESA GAIA mission will provide accurate distances and velocity vectors for millions of stars, aiding future studies. The Galaxy's complexity is challenging to describe, but its components exhibit strong overlap due to shared gravitational potential. Separating components like the bar/bulge from the inner disk and halo remains a challenge, with some arguing for a gradual transition or distinct origins for the thick and thin disks. The Galaxy's structural and kinematic parameters are crucial for comparison with other galaxies and numerical simulations. The Galaxy's distance to the center, R₀, is a key parameter, with recent estimates around 8.2 kpc. The Galaxy's position in the Tully-Fisher relation is consistent with its high circular velocity. The Galaxy's center, Sgr A*, is a supermassive black hole, with recent estimates of its mass around 4.2 million solar masses. The Galaxy's solar offset and Galactic plane are also important, with the true plane slightly inclined relative to the b=0 plane. The Galaxy's disk is nearly flat, with the long bar consistent with a tilted midplane passing through Sgr A* and the point 25 pc below the Sun. The Galaxy's black hole and solar angular velocity are well-measured, with the black hole mass consistent with other estimates. The Galaxy's future evolution and interactions with other galaxies will continue to be studied, providing insights into its dynamic history.
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