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Julio F Navarro - One of the best experts on this subject based on the ideXlab platform.
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the origin of the mass discrepancy acceleration relation in λcdm
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Julio F Navarro, Carlos S Frenk, Aaron D. Ludlow, Alejandro Benitezllambay, Matthieu Schaller, Azadeh Fattahi, Kyle A Oman, Tom TheunsAbstract:We examine the origin of the mass discrepancy–radial acceleration relation (MDAR) of disc galaxies. This is a tight empirical correlation between the disc centripetal acceleration and that expected from the baryonic component. The MDAR holds for most radii probed by disc kinematic tracers, regardless of galaxy mass or surface brightness. The relation has two characteristic accelerations: a0, above which all galaxies are baryon dominated, and amin, an effective minimum acceleration probed by kinematic tracers in isolated galaxies. We use a simple model to show that these trends arise naturally in Λ Cold Dark Matter (ΛCDM). This is because (i) disc galaxies in ΛCDM form at the centre of Dark Matter haloes spanning a relatively narrow range of virial mass; (ii) Cold Dark Matter halo acceleration profiles are self-similar and have a broad maximum at the centre, reaching values bracketed precisely by amin and a0 in that mass range and (iii) halo mass and galaxy size scale relatively tightly with the baryonic mass of a galaxy in any successful ΛCDM galaxy formation model. Explaining the MDAR in ΛCDM does not require modifications to the cuspy inner mass profiles of Dark haloes, although these may help to understand the detailed rotation curves of some dwarf galaxies and the origin of extreme outliers from the main relation. The MDAR is just a reflection of the self-similar nature of Cold Dark Matter haloes and of the physical scales introduced by the galaxy formation process.
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mass discrepancy acceleration relation a natural outcome of galaxy formation in Cold Dark Matter halos
Physical Review Letters, 2017Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Alejandro Benitezllambay, Matthieu Schaller, Tom Theuns, Richard G Bower, Joop Schaye, Robert A Crain, Azadeh FattahiAbstract:We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback implementations -- which produce different galaxy populations -- mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration, $g_{\dagger}$, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard Cold Dark Matter paradigm.
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the mass concentration redshift relation of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Volker Springel, Raul E Angulo, Michael Boylankolchin, Simon D. M. WhiteAbstract:We use the Millennium Simulation series to investigate the mass and redshift dependence of the concentration of equilibrium Cold Dark Matter (CDM) halos. We extend earlier work on the relation between halo mass profiles and assembly histories to show how the latter may be used to predict concentrations for halos of all masses and at any redshift. Our results clarify the link between concentration and the ``collapse redshift'' of a halo as well as why concentration depends on mass and redshift solely through the dimensionless ``peak height'' mass parameter, $\nu(M,z)=\delta_{\rm crit}(z)/\sigma(M,z)$. We combine these results with analytic mass accretion histories to extrapolate the $c(M,z)$ relations to mass regimes difficult to reach through direct simulation. Our model predicts that, at given $z$, $c(M)$ should deviate systematically from a simple power law at high masses, where concentrations approach a constant value, and at low masses, where concentrations are substantially lower than expected from extrapolating published empirical fits. This correction may reduce the expected self-annihilation boost factor from substructure by about one order of magnitude. The model also reproduces the $c(M,z)$ dependence on cosmological parameters reported in earlier work, and thus provides a simple and robust account of the relation between cosmology and the mass-concentration-redshift relation of CDM halos.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density, ρ, and velocity dispersion, σ, in Cold Dark Matter (CDM) haloes. In particular, we explore how closely Q ≡ ρ/σ 3 , a surrogate measure of the phase-space density, follows a power law in radius. Our study extends earlier work by considering, in addition to spherically averaged profiles, local Q estimates for individual particles, Q i ; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q i (r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q s . The resulting Q s i (r') profiles follow closely a power law near the centre, but show a clear upturn from this trend near the virial radius, r 200 . The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q ∝ r ― 1.875 in the inner, virialized regions, but departures from a power-law occur near r 200 because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of Q profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM haloes beyond their characteristic scale radius.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter halos
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density and velocity dispersion in Cold Dark Matter (CDM) halos. In particular, we explore how closely Q rho/sigma^3, a surrogate measure of the phase-space density, follows a power-law in radius. Our study extends earlier work by considering, in addition to spherically-averaged profiles, local Q-estimates for individual particles, Q_i; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q_i(r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q^s. The resulting Q_i^s(r') profiles follow closely a power law near the center, but show a clear upturn from this trend near the virial radius, r_{200}. The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q \propto r^{-1.875} in the inner, virialized regions, but departures from a power-law occur near r_{200} because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of $Q$ profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM halos beyond their characteristic scale radius.
Carlos S Frenk - One of the best experts on this subject based on the ideXlab platform.
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the origin of the mass discrepancy acceleration relation in λcdm
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Julio F Navarro, Carlos S Frenk, Aaron D. Ludlow, Alejandro Benitezllambay, Matthieu Schaller, Azadeh Fattahi, Kyle A Oman, Tom TheunsAbstract:We examine the origin of the mass discrepancy–radial acceleration relation (MDAR) of disc galaxies. This is a tight empirical correlation between the disc centripetal acceleration and that expected from the baryonic component. The MDAR holds for most radii probed by disc kinematic tracers, regardless of galaxy mass or surface brightness. The relation has two characteristic accelerations: a0, above which all galaxies are baryon dominated, and amin, an effective minimum acceleration probed by kinematic tracers in isolated galaxies. We use a simple model to show that these trends arise naturally in Λ Cold Dark Matter (ΛCDM). This is because (i) disc galaxies in ΛCDM form at the centre of Dark Matter haloes spanning a relatively narrow range of virial mass; (ii) Cold Dark Matter halo acceleration profiles are self-similar and have a broad maximum at the centre, reaching values bracketed precisely by amin and a0 in that mass range and (iii) halo mass and galaxy size scale relatively tightly with the baryonic mass of a galaxy in any successful ΛCDM galaxy formation model. Explaining the MDAR in ΛCDM does not require modifications to the cuspy inner mass profiles of Dark haloes, although these may help to understand the detailed rotation curves of some dwarf galaxies and the origin of extreme outliers from the main relation. The MDAR is just a reflection of the self-similar nature of Cold Dark Matter haloes and of the physical scales introduced by the galaxy formation process.
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mass discrepancy acceleration relation a natural outcome of galaxy formation in Cold Dark Matter halos
Physical Review Letters, 2017Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Alejandro Benitezllambay, Matthieu Schaller, Tom Theuns, Richard G Bower, Joop Schaye, Robert A Crain, Azadeh FattahiAbstract:We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback implementations -- which produce different galaxy populations -- mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration, $g_{\dagger}$, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard Cold Dark Matter paradigm.
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the mass concentration redshift relation of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Volker Springel, Raul E Angulo, Michael Boylankolchin, Simon D. M. WhiteAbstract:We use the Millennium Simulation series to investigate the mass and redshift dependence of the concentration of equilibrium Cold Dark Matter (CDM) halos. We extend earlier work on the relation between halo mass profiles and assembly histories to show how the latter may be used to predict concentrations for halos of all masses and at any redshift. Our results clarify the link between concentration and the ``collapse redshift'' of a halo as well as why concentration depends on mass and redshift solely through the dimensionless ``peak height'' mass parameter, $\nu(M,z)=\delta_{\rm crit}(z)/\sigma(M,z)$. We combine these results with analytic mass accretion histories to extrapolate the $c(M,z)$ relations to mass regimes difficult to reach through direct simulation. Our model predicts that, at given $z$, $c(M)$ should deviate systematically from a simple power law at high masses, where concentrations approach a constant value, and at low masses, where concentrations are substantially lower than expected from extrapolating published empirical fits. This correction may reduce the expected self-annihilation boost factor from substructure by about one order of magnitude. The model also reproduces the $c(M,z)$ dependence on cosmological parameters reported in earlier work, and thus provides a simple and robust account of the relation between cosmology and the mass-concentration-redshift relation of CDM halos.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density, ρ, and velocity dispersion, σ, in Cold Dark Matter (CDM) haloes. In particular, we explore how closely Q ≡ ρ/σ 3 , a surrogate measure of the phase-space density, follows a power law in radius. Our study extends earlier work by considering, in addition to spherically averaged profiles, local Q estimates for individual particles, Q i ; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q i (r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q s . The resulting Q s i (r') profiles follow closely a power law near the centre, but show a clear upturn from this trend near the virial radius, r 200 . The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q ∝ r ― 1.875 in the inner, virialized regions, but departures from a power-law occur near r 200 because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of Q profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM haloes beyond their characteristic scale radius.
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the angular momentum of Cold Dark Matter haloes with and without baryons
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Carlos S Frenk, Adrian Jenkins, Philip E Bett, V R Eke, Takashi OkamotoAbstract:We investigate the magnitude and internal alignment of the angular momentum of Cold Dark Matter haloes in simulations with and without baryons. We analyse the cumulative angular momentum profiles of hundreds of thousands of well resolved h aloes in the Millennium simulation of Springel et al. and in a smaller, but higher resolu tion, simulation, in total spanning 5 orders of magnitude in mass. For haloes of a given mass, the median specific angular momentum increases with radius as j(6 r) / r. The direction of the vector varies considerably with radius: the median angle between the inner (. 0.25Rvir) and total (6 Rvir) angular momentum vectors is about 25 ◦ . To investigate how baryons affect halo spin, we use another high-resolution simulation, which includes gas cooling, s tar formation and feedback. This simulation produces a sample of galaxies with a realistic di stribution of disc-to-total ratios, D/T : two thirds of the galaxies have D/T > 0.5 in the B-band. The formation of the galaxy spins up the Dark Matter within 0.1Rvir such that the specific halo angular momentum increases by � 50 per cent in the median. The Dark Matter angular momentum becomes better aligned, but there remains a broad distribution of (mis-)al ignments between the halo and the central galaxy, with a median angle between their angular momenta of � 30 ◦ . Galaxies have a range of orientations relative to the shape of the halo: hal f of them have their minor axes misaligned by more than 45 ◦ , although only about 10 per cent of the galaxies lie within 30 ◦ of the plane perpendicular to the major axis of their halo. Fi nally, we align a sample of haloes according to the orientation of their galaxies and stack the projected mass distributions. Although the individual haloes are significantly aspherical, galaxy‐halo misalignments produce a stacked mass distribution that cannot be distinguished fr om circular. If the lack of alignment found in our simulations is realistic, it will be extremely d ifficult for weak lensing studies to measure the ellipticity of Cold Dark Matter haloes using thi s technique.
Martha P Haynes - One of the best experts on this subject based on the ideXlab platform.
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the velocity width function of galaxies from the 40 alfalfa survey shedding light on the Cold Dark Matter overabundance problem
The Astrophysical Journal, 2011Co-Authors: Emmanouil Papastergis, Ann M Martin, Riccardo Giovanelli, Martha P HaynesAbstract:The ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey is a wide-area, extragalactic HI-line survey conducted at the Arecibo Observatory. Sources have so far been extracted over � 3000 deg 2 of sky (40% of its final area), resulting in the largest HI-selected sample to date. We measure the space density of HI-bearing galaxies as a function of their observed velocity width (uncorrected for inclination) down to w = 20 km s −1 , a factor of 2 lower than the previous generation HI Parkes All-Sky Survey. We confirm previous results that indicate a substantial discrepancy between the observational distribution and the theoretical one expected in a Cold Dark Matter (CDM) universe, at low widths. In particular, a comparison with synthetic galaxy samples populating state-of-the-art CDM simulations imply a factor of � 8 difference in the abundance of galaxies with w = 50 km s −1 (increasing to a factor of � 100 when extrapolated to the ALFALFA limit of w = 20 km s −1 ). We furthermore identify possible solutions, including a keV warm Dark Matter scenario and the fact that HI disks in low mass galaxies are usually not extended enough to probe the full amplitude of the galactic rotation curve. In this latter case, we can statistically infer the relationship between the measured HI rotational velocity of a galaxy and the mass of its host CDM halo. Observational verification of the presented relationship at low velocities would provide an important test of the validity of the established Dark Matter model. Subject headings: galaxies:statistics — Dark Matter — galaxies: dwarf — galaxies: luminosity function, mass function — radio lines: galaxies — surveys
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the velocity width function of galaxies from the 40 alfalfa survey shedding light on the Cold Dark Matter overabundance problem
arXiv: Cosmology and Nongalactic Astrophysics, 2011Co-Authors: Emmanouil Papastergis, Ann M Martin, Riccardo Giovanelli, Martha P HaynesAbstract:The ongoing Arecibo Legacy Fast ALFA (ALFALFA) survey is a wide-area, extragalactic HI-line survey conducted at the Arecibo Observatory. Sources have so far been extracted over ~3,000 sq.deg of sky (40% of its final area), resulting in the largest HI-selected sample to date. We measure the space density of HI-bearing galaxies as a function of their observed velocity width (uncorrected for inclination) down to w = 20 km/s, a factor of 2 lower than the previous generation HI Parkes All-Sky Survey. We confirm previous results that indicate a substantial discrepancy between the observational distribution and the theoretical one expected in a Cold Dark Matter (CDM) universe, at low widths. In particular, a comparison with synthetic galaxy samples populating state-of-the-art CDM simulations imply a factor of ~8 difference in the abundance of galaxies with w = 50 km/s (increasing to a factor of ~100 when extrapolated to the ALFALFA limit of w = 20 km/s). We furthermore identify possible solutions, including a keV warm Dark Matter scenario and the fact that HI disks in low mass galaxies are usually not extended enough to probe the full amplitude of the galactic rotation curve. In this latter case, we can statistically infer the relationship between the measured HI rotational velocity of a galaxy and the mass of its host CDM halo. Observational verification of the presented relationship at low velocities would provide an important test of the validity of the established Dark Matter model.
Aaron D. Ludlow - One of the best experts on this subject based on the ideXlab platform.
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the origin of the mass discrepancy acceleration relation in λcdm
Monthly Notices of the Royal Astronomical Society, 2017Co-Authors: Julio F Navarro, Carlos S Frenk, Aaron D. Ludlow, Alejandro Benitezllambay, Matthieu Schaller, Azadeh Fattahi, Kyle A Oman, Tom TheunsAbstract:We examine the origin of the mass discrepancy–radial acceleration relation (MDAR) of disc galaxies. This is a tight empirical correlation between the disc centripetal acceleration and that expected from the baryonic component. The MDAR holds for most radii probed by disc kinematic tracers, regardless of galaxy mass or surface brightness. The relation has two characteristic accelerations: a0, above which all galaxies are baryon dominated, and amin, an effective minimum acceleration probed by kinematic tracers in isolated galaxies. We use a simple model to show that these trends arise naturally in Λ Cold Dark Matter (ΛCDM). This is because (i) disc galaxies in ΛCDM form at the centre of Dark Matter haloes spanning a relatively narrow range of virial mass; (ii) Cold Dark Matter halo acceleration profiles are self-similar and have a broad maximum at the centre, reaching values bracketed precisely by amin and a0 in that mass range and (iii) halo mass and galaxy size scale relatively tightly with the baryonic mass of a galaxy in any successful ΛCDM galaxy formation model. Explaining the MDAR in ΛCDM does not require modifications to the cuspy inner mass profiles of Dark haloes, although these may help to understand the detailed rotation curves of some dwarf galaxies and the origin of extreme outliers from the main relation. The MDAR is just a reflection of the self-similar nature of Cold Dark Matter haloes and of the physical scales introduced by the galaxy formation process.
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mass discrepancy acceleration relation a natural outcome of galaxy formation in Cold Dark Matter halos
Physical Review Letters, 2017Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Alejandro Benitezllambay, Matthieu Schaller, Tom Theuns, Richard G Bower, Joop Schaye, Robert A Crain, Azadeh FattahiAbstract:We analyze the total and baryonic acceleration profiles of a set of well-resolved galaxies identified in the EAGLE suite of hydrodynamic simulations. Our runs start from the same initial conditions but adopt different prescriptions for unresolved stellar and AGN feedback, resulting in diverse populations of galaxies by the present day. Some of them reproduce observed galaxy scaling relations, while others do not. However, regardless of the feedback implementation, all of our galaxies follow closely a simple relationship between the total and baryonic acceleration profiles, consistent with recent observations of rotationally supported galaxies. The relation has small scatter: different feedback implementations -- which produce different galaxy populations -- mainly shift galaxies along the relation, rather than perpendicular to it. Furthermore, galaxies exhibit a characteristic acceleration, $g_{\dagger}$, above which baryons dominate the mass budget, as observed. These observations, consistent with simple modified Newtonian dynamics, can be accommodated within the standard Cold Dark Matter paradigm.
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the mass concentration redshift relation of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Volker Springel, Raul E Angulo, Michael Boylankolchin, Simon D. M. WhiteAbstract:We use the Millennium Simulation series to investigate the mass and redshift dependence of the concentration of equilibrium Cold Dark Matter (CDM) halos. We extend earlier work on the relation between halo mass profiles and assembly histories to show how the latter may be used to predict concentrations for halos of all masses and at any redshift. Our results clarify the link between concentration and the ``collapse redshift'' of a halo as well as why concentration depends on mass and redshift solely through the dimensionless ``peak height'' mass parameter, $\nu(M,z)=\delta_{\rm crit}(z)/\sigma(M,z)$. We combine these results with analytic mass accretion histories to extrapolate the $c(M,z)$ relations to mass regimes difficult to reach through direct simulation. Our model predicts that, at given $z$, $c(M)$ should deviate systematically from a simple power law at high masses, where concentrations approach a constant value, and at low masses, where concentrations are substantially lower than expected from extrapolating published empirical fits. This correction may reduce the expected self-annihilation boost factor from substructure by about one order of magnitude. The model also reproduces the $c(M,z)$ dependence on cosmological parameters reported in earlier work, and thus provides a simple and robust account of the relation between cosmology and the mass-concentration-redshift relation of CDM halos.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density, ρ, and velocity dispersion, σ, in Cold Dark Matter (CDM) haloes. In particular, we explore how closely Q ≡ ρ/σ 3 , a surrogate measure of the phase-space density, follows a power law in radius. Our study extends earlier work by considering, in addition to spherically averaged profiles, local Q estimates for individual particles, Q i ; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q i (r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q s . The resulting Q s i (r') profiles follow closely a power law near the centre, but show a clear upturn from this trend near the virial radius, r 200 . The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q ∝ r ― 1.875 in the inner, virialized regions, but departures from a power-law occur near r 200 because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of Q profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM haloes beyond their characteristic scale radius.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter halos
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density and velocity dispersion in Cold Dark Matter (CDM) halos. In particular, we explore how closely Q rho/sigma^3, a surrogate measure of the phase-space density, follows a power-law in radius. Our study extends earlier work by considering, in addition to spherically-averaged profiles, local Q-estimates for individual particles, Q_i; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q_i(r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q^s. The resulting Q_i^s(r') profiles follow closely a power law near the center, but show a clear upturn from this trend near the virial radius, r_{200}. The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q \propto r^{-1.875} in the inner, virialized regions, but departures from a power-law occur near r_{200} because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of $Q$ profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM halos beyond their characteristic scale radius.
Simon D. M. White - One of the best experts on this subject based on the ideXlab platform.
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the mass concentration redshift relation of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2014Co-Authors: Aaron D. Ludlow, Carlos S Frenk, Julio F Navarro, Volker Springel, Raul E Angulo, Michael Boylankolchin, Simon D. M. WhiteAbstract:We use the Millennium Simulation series to investigate the mass and redshift dependence of the concentration of equilibrium Cold Dark Matter (CDM) halos. We extend earlier work on the relation between halo mass profiles and assembly histories to show how the latter may be used to predict concentrations for halos of all masses and at any redshift. Our results clarify the link between concentration and the ``collapse redshift'' of a halo as well as why concentration depends on mass and redshift solely through the dimensionless ``peak height'' mass parameter, $\nu(M,z)=\delta_{\rm crit}(z)/\sigma(M,z)$. We combine these results with analytic mass accretion histories to extrapolate the $c(M,z)$ relations to mass regimes difficult to reach through direct simulation. Our model predicts that, at given $z$, $c(M)$ should deviate systematically from a simple power law at high masses, where concentrations approach a constant value, and at low masses, where concentrations are substantially lower than expected from extrapolating published empirical fits. This correction may reduce the expected self-annihilation boost factor from substructure by about one order of magnitude. The model also reproduces the $c(M,z)$ dependence on cosmological parameters reported in earlier work, and thus provides a simple and robust account of the relation between cosmology and the mass-concentration-redshift relation of CDM halos.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter haloes
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density, ρ, and velocity dispersion, σ, in Cold Dark Matter (CDM) haloes. In particular, we explore how closely Q ≡ ρ/σ 3 , a surrogate measure of the phase-space density, follows a power law in radius. Our study extends earlier work by considering, in addition to spherically averaged profiles, local Q estimates for individual particles, Q i ; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q i (r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q s . The resulting Q s i (r') profiles follow closely a power law near the centre, but show a clear upturn from this trend near the virial radius, r 200 . The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q ∝ r ― 1.875 in the inner, virialized regions, but departures from a power-law occur near r 200 because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of Q profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM haloes beyond their characteristic scale radius.
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secondary infall and the pseudo phase space density profiles of Cold Dark Matter halos
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Aaron D. Ludlow, Julio F Navarro, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Carlos S FrenkAbstract:We use N-body simulations to investigate the radial dependence of the density and velocity dispersion in Cold Dark Matter (CDM) halos. In particular, we explore how closely Q rho/sigma^3, a surrogate measure of the phase-space density, follows a power-law in radius. Our study extends earlier work by considering, in addition to spherically-averaged profiles, local Q-estimates for individual particles, Q_i; profiles based on the ellipsoidal radius dictated by the triaxial structure of the halo, Q_i(r'); and by carefully removing substructures in order to focus on the profile of the smooth halo, Q^s. The resulting Q_i^s(r') profiles follow closely a power law near the center, but show a clear upturn from this trend near the virial radius, r_{200}. The location and magnitude of the deviations are in excellent agreement with the predictions from Bertschinger's spherical secondary-infall similarity solution. In this model, Q \propto r^{-1.875} in the inner, virialized regions, but departures from a power-law occur near r_{200} because of the proximity of this radius to the location of the first shell crossing - the shock radius in the case of a collisional fluid. Particles there have not yet fully virialized, and so Q departs from the inner power-law profile. Our results imply that the power-law nature of $Q$ profiles only applies to the inner regions and cannot be used to predict accurately the structure of CDM halos beyond their characteristic scale radius.
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the diversity and similarity of simulated Cold Dark Matter halos
arXiv: Astrophysics, 2008Co-Authors: Julio F Navarro, Carlos S Frenk, Aaron D. Ludlow, Adrian Jenkins, Simon D. M. White, Mark Vogelsberger, Volker Springel, Jie Wang, Amina HelmiAbstract:We study the mass, velocity dispersion, and anisotropy profiles of $\Lambda$CDM halos using a suite of N-body simulations of unprecedented numerical resolution (the {\it Aquarius Project}). Our analysis confirms a number of results claimed by earlier work, and clarifies a few issues where conflicting claims may be found in the recent literature. The spherically-averaged density profile becomes progressively shallower inwards and, at the innermost resolved radius, the logarithmic slope is $\gamma \equiv -$d$\ln\rho/$d$\ln r \simlt 1$. Asymptotic inner slopes as steep as the recently claimed $\rho \propto r^{-1.2}$ are clearly ruled out. The radial dependence of $\gamma$ is well approximated by a power-law, $\gamma \propto r^{\alpha}$ (the Einasto profile). The shape parameter, $\alpha$, varies slightly but significantly from halo to halo, implying that the mass profiles of $\Lambda$CDM halos are not strictly universal: different halos cannot, in general, be rescaled to look identical. Departures from similarity are also seen in velocity dispersion profiles and correlate with those in density profiles so as to preserve a power-law form for the spherically averaged pseudo-phase-space density, $\rho/\sigma^3\propto r^{-1.875}$. Our conclusions are reliable down to radii below 0.4% of the virial radius, providing well-defined predictions for halo structure when baryonic effects are neglected, and thus an instructive theoretical template against which the modifications induced by the baryonic components of real galaxies can be judged.
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The Structure of Cold Dark Matter Halos
The Astrophysical Journal, 1995Co-Authors: Julio F Navarro, Carlos S Frenk, Simon D. M. WhiteAbstract:We use N-body simulations to investigate the structure of Dark halos in the standard Cold Dark Matter cosmogony. Halos are excised from simulations of cosmologically representative regions and are resimulated individually at high resolution. We study objects with masses ranging from those of dwarf galaxy halos to those of rich galaxy clusters. The spherically averaged density profiles of all our halos can be fit over two decades in radius by scaling a simple ``universal'' profile. The characteristic overdensity of a halo, or equivalently its concentration, correlates strongly with halo mass in a way which reflects the mass dependence of the epoch of halo formation. Halo profiles are approximately isothermal over a large range in radii, but are significantly shallower than $r^{-2}$ near the center and steeper than $r^{-2}$ near the virial radius. Matching the observed rotation curves of disk galaxies requires disk mass-to-light ratios to increase systematically with luminosity. Further, it suggests that the halos of bright galaxies depend only weakly on galaxy luminosity and have circular velocities significantly lower than the disk rotation speed. This may explain why luminosity and dynamics are uncorrelated in observed samples of binary galaxies and of satellite/spiral systems. For galaxy clusters, our halo models are consistent both with the presence of giant arcs and with the observed structure of the intracluster medium, and they suggest a simple explanation for the disparate estimates of cluster core radii found by previous authors. Our results also highlight two shortcomings of the CDM model. CDM halos are too concentrated to be consistent with the halo parameters inferred for dwarf irregulars, and the predicted abundance of galaxy halos is larger than the observed abundance of galaxies.