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Andreas Burkert - One of the best experts on this subject based on the ideXlab platform.
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the structure and dark halo core properties of dwarf spheroidal galaxies
The Astrophysical Journal, 2015Co-Authors: Andreas BurkertAbstract:The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal (DIS) model of an isothermal, non selfgravitating stellar system, in gravitational equilibrium and embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions �∗(r). Despite its constant velocity dispersion, the stellar system can be well characterised by King profiles (King 1966) with a broad distribution of Concentration Parameters c = log(r∗,t/r∗,c), with r∗,t and r∗,c the stellar tidal and core radius, respectively. The DIS model confirms the suggestion of Kormendy & Freeman (2014) that the core scale length of the stellar system, defined as a∗ = −(dln�∗/dr 2 ) −1/2 , is sensitive to the central dark matter density �0. In contrast to single-component systems, r∗,t however does not trace the tidal radius of the galaxy but the core radius rc of its dark matter halo. c is therefore sensitive to the ratio �∗/�0 with �∗ and �0 the stellar and dark matter velocity dispersion, respectively. Simple empirical relationships are derived that allow to calculate the dark halo core Parameters �0, rc and �0, given the observable quantities �∗, a∗ and c. The DIS model is applied to the Milky Way’s dSphs. Their halo velocity dispersions lie in a narrow range of 10 km/s ≤ �0 ≤ 18 km/s with halo core radii of 280 pc ≤ rc ≤ 1.3 kpc and rc ≈ 2a∗. All dSphs follow closely the same universal scaling relations h�0rci ≡ �0 × rc = 75 +8545 M⊙ pc −2 and � 2 0 ×r −1 c = 0.45 +0.51 −0.27 (km/s) 2 pc −1 that characterise the cores of more massive galaxies over a range of 18 magnitudes in blue magnitude MB. For given h�0rcithe core mass is a strong function of core radius, Mc ∼ r 2 . Inside a fixed radius ru, with ru the logarithmic mean of the dSph’s core radii, the total mass Mu = 2.17h�0rcir 2 u is however roughly constant. Outliers with smaller masses are expected for dSphs with core radii that are much larger or smaller than ru. For the Milky Way’s dSphs we find ru = 400 ± 100 pc and Mu = 2.6 ± 1.4 × 10 7 M⊙, in agreement with Strigari et al. (2008). Due to their small rc, the core densities of the Galaxy’s dSphs are very higher, with �0 = 0.03 - 0.3 M⊙ pc −3 . The dSphs would have to be on galactic orbits with pericenters smaller than a few kpc in order for their stellar systems to be affected by Galactic tides which is very unlikely. dSphs should therefore be tidally undisturbed. Observational evidence for tidal effects might then provide a serious challenge for the cold dark matter scenario.
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the structure and dark halo core properties of dwarf spheroidal galaxies
arXiv: Astrophysics of Galaxies, 2015Co-Authors: Andreas BurkertAbstract:The structure and dark matter halo core properties of dwarf spheroidal galaxies (dSphs) are investigated. A double-isothermal model of an isothermal stellar system, embedded in an isothermal dark halo core provides an excellent fit to the various observed stellar surface density distributions. The stellar system can be well characterised by King profiles with a broad distribution of Concentration Parameters c. The core scale length of the stellar system a_* is sensitive to the central dark matter density rho_0. In contrast to single-component systems, the cut-off radius of the stellar system, rs_t, however does not trace the tidal radius but the core radius r_c of its dark matter halo. c is therefore sensitive to the ratio of the stellar to the dark matter velocity dispersion, sigma_*/sigma_0. Simple empirical relationships are derived that allow to calculate the dark halo core Parameters rho_0, r_c and sigma_0, given the observable quantities sigma_*, a_* and c. The DIS model is applied to the Milky Way's dSphs. Their halo velocity dispersions lie in a narrow range of 10km/s <= sigma_0 <= 18km/s with halo core radii of 280pc <= r_c <= 1.3kpc and r_c=2a_*. All dSphs follow closely the same universal dark halo core scaling relation rho_0*r_c=75 Msolar/pc^2 that characterises the cores of more massive galaxies over several orders of magnitude in mass. The dark matter core mass is a strong function of core radius. Inside a fixed radius r_u, with r_u the logarithmic mean of the dSph's core radii, the total enclosed mass M_u is however roughly constant, although outliers should exist. For our dSphs we find r_u=400pc and M_u=2.6*10^7 Msolar. The core densities of the Galaxy's dSphs are very high, with rho_0=0.2 Msolar/pc^3. They should therefore be tidally undisturbed. Observational evidence for tidal effects might then provide a serious challenge for the cold dark matter scenario.
Andrea V Maccio - One of the best experts on this subject based on the ideXlab platform.
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Concentration spin and shape of dark matter haloes scatter and the dependence on mass and environment
Monthly Notices of the Royal Astronomical Society, 2007Co-Authors: Andrea V Maccio, Aaron A Dutton, Frank C Van Den Bosch, Ben Moore, Doug Potter, Joachim StadelAbstract:We use a series of cosmological N-body simulations for a flat A cold dark matter (ACDM) cosmology to investigate the structural properties of dark matter haloes, at redshift zero, in the mass range 3 x 10 9 h -1 ≤ M vir ≤ 3 x 10 13 h -1 M ⊙ . These properties include the Concentration parameter, c, the spin parameter, λ, and the mean axis ratio, q. For the Concentration-mass relation we find c oc M -0.11 vir agreement with the model proposed by Bullock et al., but inconsistent with the alternative model of Eke et al. The normalization of the Concentration-mass relation, however, is 15 per cent lower than suggested by Bullock et al. The results for X and q are in good agreement with previous studies, when extrapolated to the lower halo masses probed here, while c and λ are anticorrelated, in that high-spin haloes have, on average, lower Concentrations. In an attempt to remove unrelaxed haloes from the sample, we compute for each halo the offset parameter, x off , defined as the distance between the most bound particle and the centre of mass, in units of the virial radius. Removing haloes with large x off increases the mean Concentration by ∼ 10 per cent, lowers the mean spin parameter by ∼ 15 per cent, and removes the most prolate haloes. In addition, it largely removes the anticorrelation between c and λ, though not entirely. We also investigate the relation between halo properties and their large-scale environment density. For low-mass haloes we find that more concentrated haloes live in denser environments than their less concentrated counterparts of the same mass, consistent with recent correlation function analyses. Note, however, that the trend is weak compared to the scatter. For the halo spin Parameters we find no environment dependence, while there is a weak indication that the most spherical haloes reside in slightly denser environments. Finally, using a simple model for disc galaxy formation we show that haloes that host low surface brightness galaxies are expected to be hosted by a biased subset of haloes. Not only do these haloes have spin Parameters that are larger than average, they also have Concentration Parameters that are ∼15 per cent lower than the average at a given halo mass. We discuss the implications of all these findings for the claimed disagreement between halo Concentrations inferred from low surface brightness rotation curves, and those expected for a ACDM cosmology.
Christian Maulbetsch - One of the best experts on this subject based on the ideXlab platform.
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the dependence on environment of cold dark matter halo properties
The Astrophysical Journal, 2005Co-Authors: Vladimir Avilareese, Pedro Colin, Stefan Gottlober, C Firmani, Christian MaulbetschAbstract:A series of high-resolution ΛCDM cosmological N-body simulations are used to study the properties of galaxy-size dark halos as a function of global environment. We analyze halos in three types of environment: "cluster" (cluster halos and their surroundings), "void" (large regions with density contrasts -0.85), and "field" (halos not contained within larger halos). We find that halos in clusters have a median spin parameter ~1.3 times lower, a minor-to-major axial ratio ~1.2 times lower (more spherical), and a less aligned internal angular momentum than halos in voids and the field. For masses 5 × 1011 h-1 M☉, halos in cluster regions are on average ~30%-40% more concentrated and have ~2 times higher central densities than halos in voids. While for halos in cluster regions the Concentration Parameters decrease on average with mass with a slope of ~0.1, for halos in voids these Concentrations do not seem to change with mass. When comparing only parent halos from the samples, the differences are less pronounced but still significant. We obtain also the maximum circular velocity-mass and rms velocity-mass relations. These relations are shallower and more scattered for halos in clusters than in voids, and for a given circular velocity or rms velocity, the mass is smaller at z = 1 than at z = 0 for all environments. At z = 1, the differences in the halo properties with environment almost disappear, suggesting that the differences were established mainly after z ~ 1. The halos in the cluster regions undergo more dramatic changes than those in the field or the voids. The differences in halo properties with environment are due to (1) the dependence of halo formation time on global environment and (2) local effects such as tidal stripping and the tumultuous histories that halos suffer in high-density regions. We calculate seminumerical models of disk galaxy evolution using halos with the Concentrations and spin Parameters found for the different environments. For a given disk mass, the galaxy disks have higher surface density, larger maximum circular velocity and secular bulge-to-disk ratio, lower gas fraction, and are redder as one goes from void to cluster environments. Although all these trends agree with observations, the latter tend to show more differences, suggesting that physical ingredients not considered here, such as misalignment of angular momentum, halo triaxiality, merging, ram pressure stripping, harassment, etc., play an important role for galaxy evolution, especially in high-density environments.
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the dependence on environment of cold dark matter halo properties
arXiv: Astrophysics, 2005Co-Authors: Vladimir Avilareese, Pedro Colin, C Firmani, S Gottloeber, Christian MaulbetschAbstract:High-resolution LCDM cosmological N-body simulations are used to study the properties of galaxy-size dark halos in different environments (cluster, void, and "field"). Halos in clusters and their surroundings have a median spin parameter ~1.3 times lower, and tend to be more spherical and to have less aligned internal angular momentum than halos in voids and the field. For halos in clusters the Concentration Parameters decrease on average with mass with a slope of ~0.1; for halos in voids these Concentrations do not change with mass. For masses <5 10^11 M_sh^-1, halos in clusters are on average ~30-40% more concentrated and have ~2 times higher central densities than halos in voids. When comparing only parent halos, the differences are less pronounced but they are still significant. The Vmax-and Vrms-mass relations are shallower and more scattered for halos in clusters than in voids, and for a given Vmax or Vrms, the mass is smaller at z=1 than at z=0 in all the environments. At z=1, the differences in the halo properties with environment almost dissapear, suggesting this that the differences were stablished mainly after z~1. The halos in clusters undergo more dramatic changes than those in the field or the voids. The differences with environment are owing to (i) the dependence of halo formation time on environment, and (ii) local effects as tidal stripping and the tumultuos histories that halos suffer in high-density regions. We calculate seminumerical models of disk galaxy evolution in halos with the properties found for the different environments. For a given disk mass, the galaxy disks have higher surface density, larger Vd,max and secular bulge-to-disk ratio, lower gas fraction, and are redder as one goes from cluster to void environments, in rough agreement with observations. (abridged)
G P Smith - One of the best experts on this subject based on the ideXlab platform.
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direct measurement of dark matter halo ellipticity from two dimensional lensing shear maps of 25 massive clusters
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Masamune Oguri, Masahiro Takada, Nobuhiro Okabe, G P SmithAbstract:We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak-lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these Parameters on the cluster shape are little degenerate with cluster mass and Concentration Parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7σ significance level. The mean ellipticity is found to be (e) = 〈1 ― b/a〉 = 0.46 ± 0.04 (1σ), which is in excellent agreement with a theoretical prediction based on the standard collisionless cold dark matter model. The mass centroid can be constrained with a typical accuracy of ∼20 arcsec (∼50 h ―1 kpc) in radius for each cluster. The mass centroid position fairly well matches the position of the brightest cluster galaxy, with some clusters showing significant offsets. Thus, the 2D shear fitting method enables us to assess one of the most important systematic errors inherent in the stacked cluster weak-lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution or the brightest cluster galaxy. We carefully examine possible sources of systematic errors in our measurements including the effect of substructures, the cosmic shear contamination, fitting regions and the dilution effect, and find none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter, which should improve the ability of future surveys to conduct cluster cosmology experiments.
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direct measurement of dark matter halo ellipticity from two dimensional lensing shear maps of 25 massive clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Masamune Oguri, Masahiro Takada, Nobuhiro Okabe, G P SmithAbstract:We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these Parameters on the cluster shape are little degenerate with cluster mass and Concentration Parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7\sigma significance level. The mean ellipticity is found to be e = 0.46 \pm 0.04 (1\sigma), which is in excellent agreement with the standard collisionless CDM model prediction. The mass centroid can be constrained with a typical accuracy of ~20" (~50 kpc/h) in radius for each cluster with some significant outliers, enabling to assess one of the most important systematic errors inherent in the stacked cluster weak lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution. We carefully examine possible sources of systematic errors in our measurements, finding none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter (Abridged).
Nobuhiro Okabe - One of the best experts on this subject based on the ideXlab platform.
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direct measurement of dark matter halo ellipticity from two dimensional lensing shear maps of 25 massive clusters
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Masamune Oguri, Masahiro Takada, Nobuhiro Okabe, G P SmithAbstract:We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak-lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these Parameters on the cluster shape are little degenerate with cluster mass and Concentration Parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7σ significance level. The mean ellipticity is found to be (e) = 〈1 ― b/a〉 = 0.46 ± 0.04 (1σ), which is in excellent agreement with a theoretical prediction based on the standard collisionless cold dark matter model. The mass centroid can be constrained with a typical accuracy of ∼20 arcsec (∼50 h ―1 kpc) in radius for each cluster. The mass centroid position fairly well matches the position of the brightest cluster galaxy, with some clusters showing significant offsets. Thus, the 2D shear fitting method enables us to assess one of the most important systematic errors inherent in the stacked cluster weak-lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution or the brightest cluster galaxy. We carefully examine possible sources of systematic errors in our measurements including the effect of substructures, the cosmic shear contamination, fitting regions and the dilution effect, and find none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter, which should improve the ability of future surveys to conduct cluster cosmology experiments.
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direct measurement of dark matter halo ellipticity from two dimensional lensing shear maps of 25 massive clusters
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Masamune Oguri, Masahiro Takada, Nobuhiro Okabe, G P SmithAbstract:We present new measurements of dark matter distributions in 25 X-ray luminous clusters by making a full use of the two-dimensional (2D) weak lensing signals obtained from high-quality Subaru/Suprime-Cam imaging data. Our approach to directly compare the measured lensing shear pattern with elliptical model predictions allows us to extract new information on the mass distributions of individual clusters, such as the halo ellipticity and mass centroid. We find that these Parameters on the cluster shape are little degenerate with cluster mass and Concentration Parameters. By combining the 2D fitting results for a subsample of 18 clusters, the elliptical shape of dark matter haloes is detected at 7\sigma significance level. The mean ellipticity is found to be e = 0.46 \pm 0.04 (1\sigma), which is in excellent agreement with the standard collisionless CDM model prediction. The mass centroid can be constrained with a typical accuracy of ~20" (~50 kpc/h) in radius for each cluster with some significant outliers, enabling to assess one of the most important systematic errors inherent in the stacked cluster weak lensing technique, the mass centroid uncertainty. In addition, the shape of the dark mass distribution is found to be only weakly correlated with that of the member galaxy distribution. We carefully examine possible sources of systematic errors in our measurements, finding none of them to be significant. Our results demonstrate the power of high-quality imaging data for exploring the detailed spatial distribution of dark matter (Abridged).