TY - JOUR

T1 - Nihao – XVIII. Origin of the MOND phenomenology of galactic rotation curves in a CDM universe

AU - Dutton, Aaron A.

AU - Macciò, Andrea V.

AU - Obreja, Aura

AU - Buck, Tobias

N1 - Funding Information:
We thank the referee for a prompt report that led to significant improvements in the paper. The authors gratefully acknowledge the Gauss Centre for Supercomputing e.V. (www.gauss-centre.eu) for funding this project by providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Centre (http://www.lrz.de). Part of this research was also carried out on the High Performance Computing resources at New York University Abu Dhabi; on the THEO cluster of the Max-Planck-Institut für Astronomie; and on the HYDRA cluster at the Rechenzentrum in Garching. We greatly appreciate the contributions of all these computing allocations. AO is funded by the Deutsche Forschungs-gemeinschaft (DFG, German Research Foundation) – MO 2979/1-1. TB was supported by the Sonderforschungsbereich SFB 881 ‘The Milky Way System’ (subprojects A1 and A2) of the DFG. The analysis made use of the PYNBODY package (Pontzen et al. 2013).
Publisher Copyright:
© 2019 The Author(s).

PY - 2019/2/15

Y1 - 2019/2/15

N2 - The phenomenological basis for Modified Newtonian Dynamics (MOND) is the radial acceleration relation (RAR) between the observed acceleration, a = Vrot2 (r)/r, and the acceleration accounted for by the observed baryons (stars and cold gas), abar = Vbar2 (r)/r. We show that the RAR arises naturally in the NIHAO sample of 89 high-resolution CDM cosmological galaxy formation simulations. The overall scatter from NIHAO is just 0.079 dex, consistent with observational constraints. However, we show that the scatter depends on stellar mass. At high masses (109 Mstar 1011 M) the simulated scatter is just 0.04 dex, increasing to 0.11 dex at low masses (107 Mstar 109 M). Observations show a similar dependence for the intrinsic scatter. At high masses the intrinsic scatter is consistent with the zero scatter assumed by MOND, but at low masses the intrinsic scatter is non-zero, strongly disfavouring MOND. Applying MOND to our simulations yields remarkably good fits to most of the circular velocity profiles. In cases of mild disagreement the stellar mass-to-light ratio and/or ‘distance’ can be tuned to yield acceptable fits, as is often done in observational mass models. In dwarf galaxies with Mstar ∼ 106 M MOND breaks down, predicting lower accelerations than observed and in our CDM simulations. The assumptions that MOND is based on (e.g. asymptotically flat rotation curves, zero intrinsic scatter in the RAR) are only approximately true in CDM. Thus if one wishes to go beyond Newtonian dynamics there is more freedom in the observed RAR than assumed by MOND.

AB - The phenomenological basis for Modified Newtonian Dynamics (MOND) is the radial acceleration relation (RAR) between the observed acceleration, a = Vrot2 (r)/r, and the acceleration accounted for by the observed baryons (stars and cold gas), abar = Vbar2 (r)/r. We show that the RAR arises naturally in the NIHAO sample of 89 high-resolution CDM cosmological galaxy formation simulations. The overall scatter from NIHAO is just 0.079 dex, consistent with observational constraints. However, we show that the scatter depends on stellar mass. At high masses (109 Mstar 1011 M) the simulated scatter is just 0.04 dex, increasing to 0.11 dex at low masses (107 Mstar 109 M). Observations show a similar dependence for the intrinsic scatter. At high masses the intrinsic scatter is consistent with the zero scatter assumed by MOND, but at low masses the intrinsic scatter is non-zero, strongly disfavouring MOND. Applying MOND to our simulations yields remarkably good fits to most of the circular velocity profiles. In cases of mild disagreement the stellar mass-to-light ratio and/or ‘distance’ can be tuned to yield acceptable fits, as is often done in observational mass models. In dwarf galaxies with Mstar ∼ 106 M MOND breaks down, predicting lower accelerations than observed and in our CDM simulations. The assumptions that MOND is based on (e.g. asymptotically flat rotation curves, zero intrinsic scatter in the RAR) are only approximately true in CDM. Thus if one wishes to go beyond Newtonian dynamics there is more freedom in the observed RAR than assumed by MOND.

KW - Dark matter

KW - Galaxies: fundamental parameters

KW - Galaxies: haloes

KW - Galaxies: kinematics and dynamics

KW - Methods: numerical

UR - http://www.scopus.com/inward/record.url?scp=85062892604&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85062892604&partnerID=8YFLogxK

U2 - 10.1093/mnras/stz531

DO - 10.1093/mnras/stz531

M3 - Article

AN - SCOPUS:85062892604

SN - 0035-8711

VL - 485

SP - 1886

EP - 1899

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 2

ER -