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Published May 2017 | Published + Submitted
Journal Article Open

The Structure and Dynamical Evolution of the Stellar Disk of a Simulated Milky Way-Mass Galaxy

Abstract

We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty mode and have the largest vertical scaleheights (1.5–2.5 kpc) by z = 0, while stars younger than 6 Gyr were formed in a relatively calm, stable disc. The vertical scaleheight increases with stellar age at all radii, because (1) stars that formed earlier were thicker 'at birth', and (2) stars were kinematically heated to an even thicker distribution after formation. Stars of the same age are thicker in the outer disc than in the inner disc (flaring). These lead to positive vertical age gradients and negative radial age gradients. The radial metallicity gradient is negative at the mid-plane, flattens at larger disc height |Z|, and turns positive above |Z| ∼ 1.5 kpc. The vertical metallicity gradient is negative at all radii, but is steeper at smaller radii. These trends broadly agree with observations in the Milky Way and can be naturally understood from the age gradients. The vertical stellar density profile can be well described by two components, with scaleheights 200–500 pc and 1–1.5 kpc, respectively. The thick component is a mix of stars older than 4 Gyr, which formed through a combination of several mechanisms. Our results also demonstrate that it is possible to form a thin disc in cosmological simulations even with a strong stellar feedback.

Additional Information

© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 January 30. Received 2017 January 30; in original form 2016 August 14. Published: 01 February 2017. We thank David Nidever, Hans-Walter Rix, Charlie Conroy and Paul Torrey for useful discussions. We also acknowledge Oscar Agertz and Ivan Minchev for helpful comments after the first draft has appeared on arXiv, and the anonymous referee for a detailed report. The simulations used in this paper were run on XSEDE computational resources (allocations TG-AST120025, TG-AST130039 and TG-AST140023). The analysis was performed on the Caltech compute cluster 'Zwicky' (NSF MRI award #PHY-0960291). Support for PFH was provided by an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920 and CAREER grant #1455342. ARW was supported by a Caltech-Carnegie Fellowship, in part through the Moore Center for Theoretical Cosmology and Physics at Caltech. DAA acknowledges support by a CIERA Postdoctoral Fellowship. C-AF-G was supported by NSF through grants AST-1412836 and AST-1517491, by NASA through grant NNX15AB22G, and by STScI through grants HST-AR-14293.001-A and HST-GO-14268.022-A. DK was supported by NSF grant AST-1412153 and funds from the University of California, San Diego. EQ was supported by NASA ATP grant 12-APT12-0183, by a Simons Investigator award from the Simons Foundation, and by the David and Lucile Packard Foundation.

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Published - stx273.pdf

Submitted - 1608.04133v1.pdf

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Additional details

Created:
August 19, 2023
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October 23, 2023