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Title: Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?

Abstract

Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density profiles for galaxy central regions. While simulations suggest a cuspy and universal density profile (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by [1]. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy profile is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequencemore » of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.« less

Authors:
; ; ; ;  [1];  [2]
  1. Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Correo Central, Santiago (Chile)
  2. Departamento de Física, FCFM, Universidad de Chile, Blanco Encalada 2008, Santiago (Chile)
Publication Date:
OSTI Identifier:
22676194
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 05; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COSMOLOGICAL MODELS; DENSITY; DISTRIBUTION; DISTRIBUTION FUNCTIONS; FOKKER-PLANCK EQUATION; GALAXIES; INTERACTIONS; NONLUMINOUS MATTER; RELIABILITY; SIMULATION; STREAMS; VELOCITY

Citation Formats

Baushev, A.N., Valle, L. del, Campusano, L.E., Escala, A., Muñoz, R.R., and Palma, G.A., E-mail: baushev@gmail.com, E-mail: ldelvalleb@gmail.com, E-mail: luis@das.uchile.cl, E-mail: aescala@das.uchile.cl, E-mail: rmunoz@das.uchile.cl, E-mail: gpalmaquilod@ing.uchile.cl. Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/05/042.
Baushev, A.N., Valle, L. del, Campusano, L.E., Escala, A., Muñoz, R.R., & Palma, G.A., E-mail: baushev@gmail.com, E-mail: ldelvalleb@gmail.com, E-mail: luis@das.uchile.cl, E-mail: aescala@das.uchile.cl, E-mail: rmunoz@das.uchile.cl, E-mail: gpalmaquilod@ing.uchile.cl. Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?. United States. doi:10.1088/1475-7516/2017/05/042.
Baushev, A.N., Valle, L. del, Campusano, L.E., Escala, A., Muñoz, R.R., and Palma, G.A., E-mail: baushev@gmail.com, E-mail: ldelvalleb@gmail.com, E-mail: luis@das.uchile.cl, E-mail: aescala@das.uchile.cl, E-mail: rmunoz@das.uchile.cl, E-mail: gpalmaquilod@ing.uchile.cl. Mon . "Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?". United States. doi:10.1088/1475-7516/2017/05/042.
@article{osti_22676194,
title = {Cusps in the center of galaxies: a real conflict with observations or a numerical artefact of cosmological simulations?},
author = {Baushev, A.N. and Valle, L. del and Campusano, L.E. and Escala, A. and Muñoz, R.R. and Palma, G.A., E-mail: baushev@gmail.com, E-mail: ldelvalleb@gmail.com, E-mail: luis@das.uchile.cl, E-mail: aescala@das.uchile.cl, E-mail: rmunoz@das.uchile.cl, E-mail: gpalmaquilod@ing.uchile.cl},
abstractNote = {Galaxy observations and N-body cosmological simulations produce conflicting dark matter halo density profiles for galaxy central regions. While simulations suggest a cuspy and universal density profile (UDP) of this region, the majority of observations favor variable profiles with a core in the center. In this paper, we investigate the convergency of standard N-body simulations, especially in the cusp region, following the approach proposed by [1]. We simulate the well known Hernquist model using the SPH code Gadget-3 and consider the full array of dynamical parameters of the particles. We find that, although the cuspy profile is stable, all integrals of motion characterizing individual particles suffer strong unphysical variations along the whole halo, revealing an effective interaction between the test bodies. This result casts doubts on the reliability of the velocity distribution function obtained in the simulations. Moreover, we find unphysical Fokker-Planck streams of particles in the cusp region. The same streams should appear in cosmological N-body simulations, being strong enough to change the shape of the cusp or even to create it. Our analysis, based on the Hernquist model and the standard SPH code, strongly suggests that the UDPs generally found by the cosmological N-body simulations may be a consequence of numerical effects. A much better understanding of the N-body simulation convergency is necessary before a 'core-cusp problem' can properly be used to question the validity of the CDM model.},
doi = {10.1088/1475-7516/2017/05/042},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 05,
volume = 2017,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}