On the flaring of thick discs of galaxies: insights from simulations

Abstract

Using simulated galaxies in their cosmological context, we analyse how the flaring of mono-age populations (MAPs) influences the flaring and the age structure of geometrically defined thick discs. We also explore under which circumstances the geometric thin and thick discs are meaningfully distinct components, or are part of a single continuous structure as in the Milky Way. We find that flat thick discs are created when MAPs barely flare or have low surface density at the radius where they start flaring. When looking at the vertical distribution of MAPs, these galaxies show a continuous thin/thick structure. They also have radial age gradients and tend to have quiescent merger histories. Those characteristics are consistent with what is observed in the Milky Way. Flared thick discs, on the other hand, are created when the MAPs that flare have a high surface density at the radius where they start flaring. The thick discs’ scale heights can either be dominated by multiple MAPs or just a few, depending on the mass and scale height distribution of the MAPs. In a large fraction of these galaxies, thin and thick discs are clearly distinct structures. Finally, flared thick discs have diverse radial age gradients and merger histories, with galaxies that are more massive or that have undergone massive mergers showing flatter age radial gradients in their thick disc.

Mapping the Galactic Disk with the LAMOST and Gaia Red Clump Sample VII: the Stellar Disk Structure Revealed by the Mono-abundance Populations

“…Our flared vertical profiles for the thin and thick disks are in good agreement with the predection of thin+thick flaring disk model (López-Corredoira & Molgo 2014), and are consistent with the number simulations of the chemodynamical evolution in Galactic disks formed in the cosmological context (Minchev et al 2013(Minchev et al , 2014(Minchev et al , 2015(Minchev et al , 2017, as well as the cosmological zoom simulation of VINTERGATAN (Agertz et al 2020). These model simulations suggest that the vertical flaring trends are a natural consequence of inside out, up-side down growth coupled with disk flaring (see also Bird et al 2013;García de la Cruz et al 2021), which allows for the low-[α/Fe] stars to exist several kpc above the disk's midplane. As analyzed by B16, the exponential flaring profiles for the low-[α/Fe] MAPs suggests that radial migration played an important role in the formation and evolution of the thin disk.…”

Dynamical interplay of disc thickness and the interstellar gas: implication for the longevity of spiral density waves

“…López-Corredoira & Molgó (2014) showed that the Galactic disc flares substantially between Galactocentric radii 8 kpc to 25 kpc (also see Li et al 2019) with the thin-disc component having a scale-height of ∼ 300 pc in the Solar neighbourhood (e. g., see Jurić et al 2008). This flaring of galactic disc (i.e., increment of scale-height) is a generic phenomenon (e.g., see de Grijs & Peletier 1997;Narayan & Jog 2002a;Sarkar & Jog 2019;García de la Cruz et al 2021). In addition, the existence of a thick-disc component is now wellestablished observationally in both, external galaxies, as well as the Milky Way (e.g., see Tsikoudi 1979;Burstein 1979;Yoachim & Dalcanton 2006;Comerón et al 2011aComerón et al ,b, 2018.…”

Dynamical interplay of disc thickness and interstellar gas: Implication for the longevity of spiral density waves

“…increment of the scale height) is a generic phenomenon (e.g. see de Grijs & Peletier 1997;Narayan & Jog 2002a;Sarkar & Jog 2019; García de la Cruz et al 2021). In addition, the existence of a thick-disc component is now well established observationally in external galaxies as well as in the Milky Way (e.g.…”