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The origin of the diverse morphologies and kinematics of Milky Way-mass galaxies in the FIRE-2 simulations

Garrison-Kimmel, Shea, Hopkins, Philip F., Wetzel, Andrew, El-Badry, Kareem, Sanderson, Robyn E., Bullock, James S., Ma, Xiangcheng, van de Voort, Freeke, Hafen, Zachary, Faucher-Giguère, Claude-André, Hayward, Christopher C., Quataert, Eliot, Kereš, Dušan and Boylan-Kolchin, Michael 2018. The origin of the diverse morphologies and kinematics of Milky Way-mass galaxies in the FIRE-2 simulations. Monthly Notices of the Royal Astronomical Society 481 (3) , pp. 4133-4157. 10.1093/mnras/sty2513

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Abstract

We use hydrodynamic cosmological zoom-in simulations from the Feedback in Realistic Environments project to explore the morphologies and kinematics of 15 Milky Way (MW)-mass galaxies. Our sample ranges from compact, bulge-dominated systems with 90 per cent of their stellar mass within 2.5 kpc to well-ordered discs that reach ≳15 kpc. The gas in our galaxies always forms a thin, rotation-supported disc at z = 0, with sizes primarily determined by the gas mass. For stars, we quantify kinematics and morphology both via the fraction of stars on disc-like orbits and with the radial extent of the stellar disc. In this mass range, stellar morphology and kinematics are poorly correlated with the properties of the halo available from dark matter-only simulations (halo merger history, spin, or formation time). They more strongly correlate with the gaseous histories of the galaxies: those that maintain a high gas mass in the disc after z ∼ 1 develop well-ordered stellar discs. The best predictor of morphology we identify is the spin of the gas in the halo at the time the galaxy formed 1/2 of its stars (i.e. the gas that builds the galaxy). High-z mergers, before a hot halo emerges, produce some of the most massive bulges in the sample (from compact discs in gas-rich mergers), while later-forming bulges typically originate from internal processes, as satellites are stripped of gas before the galaxies merge. Moreover, most stars in z = 0 MW-mass galaxies (even z = 0 bulge stars) form in a disc: ≳60--90 per cent of stars begin their lives rotationally supported.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Physics and Astronomy
Publisher: Oxford University Press
ISSN: 0035-8711
Date of First Compliant Deposit: 9 March 2020
Date of Acceptance: 10 September 2018
Last Modified: 10 Mar 2020 11:10
URI: http://orca.cardiff.ac.uk/id/eprint/130242

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