The innate origin of radial and vertical gradients in a simulated galaxy disc

We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrody- namical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to inter...

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Bibliographic Details
Published in:arXiv.org 2018-01
Main Authors: Navarro, Julio F, Cameron Yozin, Loewen, Nic, Benitez-Llambay, Alejandro, Fattahi, Azadeh, Frenk, Carlos S, Oman, Kyle, Schaye, Joop, Theuns, Tom
Format: Article
Language:English
Subjects:
Enrichment
Galactic evolution
Kinematics
Metallicity
Migration
Milky Way Galaxy
Molecular clouds
Scattering
Simulation
Star & galaxy formation
Star formation
Stars
Stars & galaxies
Stellar age
Stellar evolution
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Summary:We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrody- namical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital reso- nances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration timescales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.
ISSN:2331-8422
DOI:10.48550/arxiv.1709.01040