MaGICC thick disc - I. Comparing a simulated disc formed with stellar feedback to the Milky Way

• Published in: Monthly notices of the Royal Astronomical Society Vol. 436; no. 1; pp. 625 - 634
• Main Authors: Stinson, G. S., Bovy, J., Rix, H.-W., Brook, C., Roškar, R., Dalcanton, J. J., Macciò, A. V., Wadsley, J., Couchman, H. M. P., Quinn, T. R.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21-11-2013
• Subjects: Astronomy; Comparative studies; Milky Way; Simulation; galaxies: formation; galaxies: structure; hydrodynamics
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stt1600

We analyse the structure and chemical enrichment of a Milky Way-like galaxy with a stellar mass of 2 × 1010 M, formed in a cosmological hydrodynamical simulation. It is disc dominated with a flat rotation curve, and has a disc scalelength similar to the Milky Way's, but a velocity dispersion that is ∼50 per cent higher. Examining stars in narrow [Fe/H] and [α/Fe] abundance ranges, we find remarkable qualitative agreement between this simulation and observations. (a) The old stars lie in a thickened distribution with a short scalelength, while the young stars form a thinner disc, with scalelengths decreasing, as [Fe/H] increases. (b) Consequently, there is a distinct outward metallicity gradient. (c) Mono-abundance populations exist with a continuous distribution of scaleheights (from thin to thick). However, the simulated galaxy has a distinct and substantive very thick disc (h
z
∼ 1.5 kpc), not seen in the Milky Way. The broad agreement between simulations and observations allows us to test the validity of observational proxies used in the literature: we find in the simulation that mono-abundance populations are good proxies for single age populations (<1 Gyr) for most abundances.