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The vertical structure of gaseous galaxy discs in cold dark matter haloes

Benítez-Llambay, Alejandro; Navarro, Julio F.; Frenk, Carlos S.; Ludlow, Aaron D.

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Authors

Alejandro Benítez-Llambay

Julio F. Navarro

Aaron D. Ludlow



Abstract

We study the vertical structure of polytropic centrifugally supported gaseous discs embedded in cold dark matter (CDM) haloes. At fixed radius, R, the shape of the vertical density profile depends weakly on whether the disc is self-gravitating (SG) or non-self-gravitating (NSG). The disc ‘characteristic’ thickness, zH, set by the midplane sound speed and circular velocity, zNSG = (cs/Vc)R, in the NSG case, and by the sound speed and surface density, zSG=c2s/GΣ zSG=cs2/GΣ , in SG discs, is smaller than zSG and zNSG. SG discs are typically Toomre unstable, NSG discs are stable. Exponential discs in CDM haloes with roughly flat circular velocity curves ‘flare’ outwards. Flares in mono abundance or coeval populations in galaxies like the Milky Way are thus not necessarily due to radial migration. For the polytropic equation of state of the Evolution and Assembly of GaLaxies and their Environments (EAGLE) simulations, discs that match observational constraints are NSG for Md < 3 × 109 M⊙ and SG at higher masses, if fully gaseous. We test these analytic results using a set of idealized smoothed particle hydrodynamic simulations and find excellent agreement. Our results clarify the role of the gravitational softening on the thickness of simulated discs, and on the onset of radial instabilities. EAGLE low-mass discs are NSG so the softening plays no role in their vertical structure. High-mass discs are expected to be SG and unstable, and may be artificially thickened and stabilized unless gravity is well resolved. Simulations with spatial resolution high enough to not compromise the vertical structure of a disc also resolve the onset of their instabilities, but the converse is not true.

Citation

Benítez-Llambay, A., Navarro, J. F., Frenk, C. S., & Ludlow, A. D. (2018). The vertical structure of gaseous galaxy discs in cold dark matter haloes. Monthly Notices of the Royal Astronomical Society, 473(1), 1019-1037. https://doi.org/10.1093/mnras/stx2420

Journal Article Type Article
Acceptance Date Sep 12, 2017
Online Publication Date Sep 22, 2017
Publication Date Jan 1, 2018
Deposit Date Jan 25, 2018
Publicly Available Date Mar 29, 2024
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 473
Issue 1
Pages 1019-1037
DOI https://doi.org/10.1093/mnras/stx2420

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.





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