The structure and dynamical evolution of the stellar disc of a simulated Milky Way-mass galaxy

By Xiangcheng Ma, P. Hopkins, Andrew Wetzel, E. Kirby, Daniel Anglés-Alcázar, C. Faucher-Giguére, D. Keres̆, Eliot Quataert Caltech, Northwestern, Ucsd and 1 more. 2016

118 citations recorded by the source corpus.

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.

Subfields: Astronomy and Astrophysics

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Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “…et al. 2014, Gaia-ESO - Recio-Blanco et al. 2014, LAMOST - Wang et al. 2019), explained by Minchev et al. (2014a) (see also Rahimi et al. 2014; Miranda et al. 2016; Ma et al. 2017; Schönrich & McMillan 2017) as the effect of inside-out disk formation and disk flaring2 of mono-age populations (Fig.”
Black holes on FIRE: stellar feedback limits early feeding of galactic nuclei (2017, background): “…in FIRE simulations, in which early bursty star formation transitions to long-lived gaseous discs with more time-steady star formation in more massive and lower-redshift galaxies (Muratov et al. 2015; Anglés-Alcázar et al. 2017b; Faucher-Giguère 2017; Hayward & Hopkins 2017; Ma et al. 2017a,b).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…structure of dwarfs (Oñorbe et al. 2015; Chan et al. 2015; Wheeler et al. 2015, 2017; Wetzel et al. 2016); abundance gradients (El-Badry et al. 2016; Ma et al. 2017a); neutral hydrogen absorption in the CGM (Faucher-Giguere et al. 2015; Faucher-Giguère et al. 2016; Hafen et al. 2017); galactic…”
Estimating stellar birth radii and the time evolution of Milky Way’s ISM metallicity gradient (2018, background): “This inversion was explained by Minchev et al. (2014a) (hereafter, MCM14, see also Rahimi et al. 2014; Miranda et al. 2016; Ma et al. 2017) as the effect of inside-out disk formation and disk flaring of monoage populations (their Fig.”
The influence of Sagittarius and the Large Magellanic Cloud on the stellar disc of the Milky Way Galaxy (2017, background): “We also note that our experiment lacks a cosmological context under which the Galaxy as a whole is growing and interacting with its subhaloes (Aumer & White 2013; Grand et al. 2017; Ma et al. 2017).”
Predicting the LISA white dwarf binary population in the Milky Way with cosmological simulations (2019, background): “Its global star formation history is consistent with the MW (see Ma et al. 2017 for illustrations) although its present day star formation rate of 6M yr−1 is somewhat higher than observed in the Milky Way.”