Skip to main content

Research Repository

Advanced Search

The origin of discs and spheroids in simulated galaxies

Sales, Laura V.; Navarro, Julio F.; Theuns, Tom; Schaye, Joop; White, Simon D.M.; Frenk, Carlos S.; Crain, Robert A.; Dalla Vecchia, Claudio

The origin of discs and spheroids in simulated galaxies Thumbnail


Laura V. Sales

Julio F. Navarro

Joop Schaye

Simon D.M. White

Robert A. Crain

Claudio Dalla Vecchia


The major morphological features of a galaxy are thought to be determined by the assembly history and net spin of its surrounding dark halo. In the simplest scenario, disc galaxies form predominantly in haloes with high angular momentum and quiet recent assembly history, whereas spheroids are the slowly rotating remnants of repeated merging events. We explore these assumptions using 100 systems with halo masses similar to that of the Milky Way, identified in a series of cosmological gasdynamical simulations: the Galaxies–Intergalactic Medium Interaction Calculation (GIMIC). At z= 0, the simulated galaxies exhibit a wide variety of morphologies, from dispersion-dominated spheroids to pure disc galaxies. Surprisingly, these morphological features are very poorly correlated with their halo properties: discs form in haloes with high and low net spin, and mergers play a negligible role in the formation of spheroids, whose stars form primarily in situ. With hindsight, this weak correlation between halo and galaxy properties is unsurprising given that a minority of the available baryons (∼40 per cent) end up in galaxies. More important to morphology is the coherent alignment of the angular momentum of baryons that accrete over time to form a galaxy. Spheroids tend to form when the spin of newly accreted gas is misaligned with that of the extant galaxy, leading to the episodic formation of stars with different kinematics that cancel out the net rotation of the system. Discs, on the other hand, form out of gas that flows in with similar angular momentum to that of earlier accreted material. Gas accretion from a hot corona thus favours disc formation, whereas gas that flows ‘cold’, often along separate, misaligned filaments, favours the formation of spheroids. In this scenario, many spheroids consist of the superposition of stellar components with distinct kinematics, age and metallicity, an arrangement that might survive to the present day given the paucity of major mergers. Since angular momentum is acquired largely at turnaround, morphology depends on the early interplay between the tidal field and the shape of the material destined to form a galaxy.


Sales, L. V., Navarro, J. F., Theuns, T., Schaye, J., White, S. D., Frenk, C. S., …Dalla Vecchia, C. (2012). The origin of discs and spheroids in simulated galaxies. Monthly Notices of the Royal Astronomical Society, 423(2), 1544-1555.

Journal Article Type Article
Acceptance Date Mar 22, 2012
Online Publication Date Jun 21, 2012
Publication Date Jun 21, 2012
Deposit Date Mar 6, 2013
Publicly Available Date Apr 22, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 423
Issue 2
Pages 1544-1555


Published Journal Article (1.9 Mb)

Copyright Statement
This article has been accepted for publication in Monthly notices of the Royal Astronomical Society ©: 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

You might also like

Downloadable Citations