Numerical simulation of a possible origin of the positive radial metallicity gradient of the thick disk

By A. Rahimi, K. Carrell, Daisuke Kawata. 2013

15 citations recorded by the source corpus.

We analyze the radial and vertical metallicity and [α/Fe] gradients of the disk stars of a disk galaxy simulated in a fully cosmological setting with the chemo-dynamical galaxy evolution code GCD+. We study how the radial abundance gradients vary as a function of height above the plane and find that the metallicity ([α/Fe]) gradient becomes more positive (negative) with increasing height, changing sign around 1.5 kpc above the plane. At the largest vertical height (2 < |z| < 3 kpc), our simulated galaxy shows a positive radial metallicity gradient. We find that the positive metallicity gradient is caused by the age-metallicity and age-velocity dispersion relation, where younger stars have higher metallicity and lower velocity dispersion. Due to the age-velocity dispersion relation, a greater fraction of younger stars reaches |z| > 2 kpc at the outer region, because of the lower gravitational restoring force of the disk, i.e. flaring. As a result, the fraction of younger stars with higher metallicity due to the age-metallicity relation becomes higher at the outer radii, which makes the median metallicity higher at the outer radii. Combining this result with the recently observed age-metallicity and age-velocity dispersion relation for the Milky Way thick disk stars suggested by Haywood et al., we argue that the observed (small) positive radial metallicity gradient at large heights of the Milky Way disk stars can be explained by flaring of the younger thick and/or thin disk stars.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Yule-Simpson’s paradox in Galactic Archaeology (2019, background): “…2013b, APOGEE - Anders 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…”
Impacts of a flaring star-forming disc and stellar radial mixing on the vertical metallicity gradient (2016, background): “Analysing a cosmological simulation result, Rahimi et al. (2014) found that the old compact thick disc population and the flaring younger thinner disc population leads to a negative radial metallicity gradient at the disc plane, and a positive radial metallicity gradient at the high vertical…”
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 vertical metallicity gradients of mono-age stellar populations in the Milky Way with the RAVE and Gaia data (2017, background): “It is not impossible to expect that all the thin disc stars formed in a flaring star-forming region (e.g. Rahimi et al. 2014; Minchev et al. 2015).”