Knowra Thick disk Thick disk A flattened, extended stellar component of a galaxy whose stars occupy a greater vertical range than the thin disk. Thick-disk stars are typically older and have different chemical and kinematic properties.
Stellar kinematics : The motions and velocity distributions of stars within a galaxy or stellar system. Thick-disk stars have distinctive vertical motions and orbital patterns that help identify the component.
Galaxy merger : An interaction in which two galaxies combine through gravity into a single system. A past merger can heat a pre-existing disk and contribute stars to a thick component.
Thin disk : The flattened, relatively narrow stellar component of a galaxy, often associated with ongoing star formation. It is the neighboring disk component with a smaller vertical extent and generally younger stars.
Milky Way thick disk : The vertically extended stellar component of the Milky Way, identified through its structure, motions, ages, and chemistry. It is the canonical nearby case for studying a thick disk star by star.
Galactic chemical evolution : The changes in a galaxy’s chemical composition as stars form, evolve, and return elements to interstellar space. Thick-disk abundance patterns encode the enrichment history of the gas from which its stars formed.
Gas-rich galaxy merger : A merger between galaxies containing substantial cold gas, capable of triggering rapid star formation. Such mergers can build a thick stellar population during a turbulent, early phase of disk formation.
Stellar halo : The diffuse, roughly spherical stellar component surrounding a galaxy’s central regions and disk. Its extended, often eccentric stellar orbits differ from the thick disk’s flattened structure.
Alpha-enhanced stars : Stars with elevated ratios of alpha elements, such as magnesium and silicon, relative to iron. Many Milky Way thick-disk stars show alpha enhancement, indicating rapid early chemical enrichment.
Vertical structure of galaxies : The distribution of stars, gas, and dust perpendicular to a galaxy’s disk plane. The thick disk is defined in part by its extended distribution above and below the plane.
Clumpy disk formation : The growth of massive star-forming clumps in a gas-rich galactic disk and their dynamical evolution. Clump interactions can heat disk stars and contribute to a thick stellar layer.
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