The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform

Léon V. E. Koopmans - One of the best experts on this subject based on the ideXlab platform.

  • The SWELLS survey. IV. Precision measurements of the stellar and dark matter Distributions in a spiral lens galaxy
    Monthly Notices of the Royal Astronomical Society, 2012
    Co-Authors: Matteo Barnabè, Matthew W. Auger, Tommaso Treu, Adam S. Bolton, Aaron A. Dutton, Philip J. Marshall, Brendon J. Brewer, David C. Koo, Léon V. E. Koopmans
    Abstract:

    We construct a fully self-consistent mass model for the lens galaxy J2141 at z=0.14, and use it to improve on previous studies by modelling its gravitational lensing effect, gas rotation curve and stellar kinematics simultaneously. We adopt a very flexible axisymmetric mass model constituted by a generalized NFW dark matter halo and a stellar mass Distribution obtained by deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of the galaxy, with the (spatially constant) M/L ratio as a free parameter. We model the stellar kinematics by solving the anisotropic Jeans equations. We find that the inner logarithmic slope of the dark halo is weakly constrained (gamma = 0.82^{+0.65}_{-0.54}), and consistent with an unmodified NFW profile. We infer the galaxy to have (i) a dark matter fraction within 2.2 disk radii of 0.28^{+0.15}_{-0.10}, independent of the galaxy stellar population, implying a maximal disk for J2141; (ii) an apparently uncontracted dark matter halo, with concentration c_{-2} = 7.7_{-2.5}^{+4.2} and virial velocity v_{vir} = 242_{-39}^{+44} km/s, consistent with LCDM predictions; (iii) a slightly oblate halo (q_h = 0.75^{+0.27}_{-0.16}), consistent with predictions from baryon-affected models. Comparing the stellar mass inferred from the combined analysis (log_{10} Mstar/Msun = 11.12_{-0.09}^{+0.05}) with that inferred from SPS modelling of the galaxies colours, and accounting for a cold gas fraction of 20+/-10%, we determine a preference for a Chabrier IMF over Salpeter IMF by a Bayes factor of 5.7 (substantial evidence). We infer a value beta_{z} = 1 - sigma^2_{z}/sigma^2_{R} = 0.43_{-0.11}^{+0.08} for the orbital anisotropy parameter in the meridional plane, in agreement with most studies of local disk galaxies, and ruling out at 99% CL that the dynamics of this system can be described by a two-Integral Distribution Function. [Abridged]

  • The non‐evolving internal structure of early‐type galaxies: the case study SDSS J0728+3835 at z= 0.206
    Monthly Notices of the Royal Astronomical Society, 2010
    Co-Authors: Matteo Barnabè, Léon V. E. Koopmans, Matthew W. Auger, Tommaso Treu, Adam S. Bolton, Oliver Czoske, Raphael Gavazzi
    Abstract:

    We study the internal dynamical structure of the early-type lens galaxy SDSS J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on lensing geometry and on stellar mass estimates obtained from multiband Hubble Space Telescope imaging. The data are modelled under the assumptions of axial symmetry supported by a two-Integral Distribution Function, by applying the combined gravitational lensing and stellar dynamics code cauldron and by yielding high-quality constraints for an early-type galaxy at cosmological redshifts. Modelling the total density profile as a power law of the form , we find that it is nearly isothermal (logarithmic slope gamma' = 2.08+0.04(-0.02)) and quite flattened (axial ratio q = 0.60+0.08(-0.03)). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02) and shows a fair amount of rotational support, in particular towards the outer regions. We determine a dark matter fraction lower limit of 28 per cent within the effective radius. The stellar contribution to the total mass Distribution is close to maximal for a Chabrier initial mass Function (IMF), whereas for a Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner regions. We find that the combination of a Navarro, Frenk and White dark matter halo with the maximally rescaled luminous profile provides a remarkably good fit to the total mass Distribution over a broad radial range. Our results confirm and expand the findings of the Sloan Lens ACS Survey for early-type galaxies of comparable velocity dispersion (Sigma(SDSS) = 214 +/- 11 km s-1). The internal structure of SDSS J0728 is consistent with that of local early-type galaxies of comparable velocity dispersion as measured by the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) project, suggesting lack of evolution in the past two billion years.

  • Crash-testing the CAULDRON code for joint lensing and dynamics analysis of early-type galaxies
    Monthly Notices of the Royal Astronomical Society, 2009
    Co-Authors: Matteo Barnabè, Carlo Nipoti, Léon V. E. Koopmans, S. Vegetti, Luca Ciotti
    Abstract:

    We apply the joint lensing and dynamics code for the analysis of early-type galaxies, CAULDRON, to a rotating N-body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-Integral Distribution Function. The goal is to study how CAULDRON performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N-body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density Distribution. We find that several global properties of the N-body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density Distribution. In particular, the logarithmic slope of the total density Distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true Distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ~ 10 per cent of the total mass. Unless the line of sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the V/sigma ratio, and the anisotropy parameter delta. We conclude that the CAULDRON code can be safely and effectively applied to real early-type lens galaxies, providing reliable information also for systems that depart significantly from the method's assumptions.

  • A Unifying Framework for Self-consistent Gravitational Lensing and Stellar Dynamics Analyses of Early-Type Galaxies
    The Astrophysical Journal, 2007
    Co-Authors: Matteo Barnabè, Léon V. E. Koopmans
    Abstract:

    Gravitational lensing and stellar dynamics are two independent methods, based solely on gravity, to study the mass Distributions of galaxies. Both methods suffer from degeneracies, however, that are difficult to break. In this paper, we present a new framework that self-consistently unifies gravitational lensing and stellar dynamics. This approach breaks some of classical degeneracies that have limited their individual usage, in particular in the study of high-redshift galaxies. The methodology is based on the premise that, for any given galaxy potential, the mapping of both the unknown lensed source brightness Distribution and the stellar phase-space Distribution Function on to the photometric and kinematic observables, can be cast as a single set of coupled linear equations. This set of linear equations is solved, maximizing the likelihood penalty Function. The evidence penalty Function, as derived from Bayesian statistics, subsequently allows the best potential-model parameters to be found and potential-model families, or other model assumptions (e.g. PSF), to be quantitatively ranked. We have implemented a fast algorithm that solves for the maximum-likelihood pixelized lensed source brightness Distribution and the two-Integral stellar phase-space Distribution Function f(E, L_z), assuming axisymmetric potentials. To make the method practical, we have devised a new Monte-Carlo approach to Schwarzschild's orbital superposition method, based on the superposition of two-Integral (E and L_z) toroidal components, to find the maximum-likelihood two-Integral Distribution Function in a matter of seconds in any axisymmetric potential. The non-linear parameters of the potential are subsequently found through a hybrid MCMC and Simplex optimization of the evidence. (Abridged)

Matteo Barnabè - One of the best experts on this subject based on the ideXlab platform.

  • The SWELLS survey. IV. Precision measurements of the stellar and dark matter Distributions in a spiral lens galaxy
    Monthly Notices of the Royal Astronomical Society, 2012
    Co-Authors: Matteo Barnabè, Matthew W. Auger, Tommaso Treu, Adam S. Bolton, Aaron A. Dutton, Philip J. Marshall, Brendon J. Brewer, David C. Koo, Léon V. E. Koopmans
    Abstract:

    We construct a fully self-consistent mass model for the lens galaxy J2141 at z=0.14, and use it to improve on previous studies by modelling its gravitational lensing effect, gas rotation curve and stellar kinematics simultaneously. We adopt a very flexible axisymmetric mass model constituted by a generalized NFW dark matter halo and a stellar mass Distribution obtained by deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of the galaxy, with the (spatially constant) M/L ratio as a free parameter. We model the stellar kinematics by solving the anisotropic Jeans equations. We find that the inner logarithmic slope of the dark halo is weakly constrained (gamma = 0.82^{+0.65}_{-0.54}), and consistent with an unmodified NFW profile. We infer the galaxy to have (i) a dark matter fraction within 2.2 disk radii of 0.28^{+0.15}_{-0.10}, independent of the galaxy stellar population, implying a maximal disk for J2141; (ii) an apparently uncontracted dark matter halo, with concentration c_{-2} = 7.7_{-2.5}^{+4.2} and virial velocity v_{vir} = 242_{-39}^{+44} km/s, consistent with LCDM predictions; (iii) a slightly oblate halo (q_h = 0.75^{+0.27}_{-0.16}), consistent with predictions from baryon-affected models. Comparing the stellar mass inferred from the combined analysis (log_{10} Mstar/Msun = 11.12_{-0.09}^{+0.05}) with that inferred from SPS modelling of the galaxies colours, and accounting for a cold gas fraction of 20+/-10%, we determine a preference for a Chabrier IMF over Salpeter IMF by a Bayes factor of 5.7 (substantial evidence). We infer a value beta_{z} = 1 - sigma^2_{z}/sigma^2_{R} = 0.43_{-0.11}^{+0.08} for the orbital anisotropy parameter in the meridional plane, in agreement with most studies of local disk galaxies, and ruling out at 99% CL that the dynamics of this system can be described by a two-Integral Distribution Function. [Abridged]

  • The non‐evolving internal structure of early‐type galaxies: the case study SDSS J0728+3835 at z= 0.206
    Monthly Notices of the Royal Astronomical Society, 2010
    Co-Authors: Matteo Barnabè, Léon V. E. Koopmans, Matthew W. Auger, Tommaso Treu, Adam S. Bolton, Oliver Czoske, Raphael Gavazzi
    Abstract:

    We study the internal dynamical structure of the early-type lens galaxy SDSS J0728+3835 at z = 0.206. The analysis is based on two-dimensional kinematic maps extending out to 1.7 effective radii obtained from Keck spectroscopy, on lensing geometry and on stellar mass estimates obtained from multiband Hubble Space Telescope imaging. The data are modelled under the assumptions of axial symmetry supported by a two-Integral Distribution Function, by applying the combined gravitational lensing and stellar dynamics code cauldron and by yielding high-quality constraints for an early-type galaxy at cosmological redshifts. Modelling the total density profile as a power law of the form , we find that it is nearly isothermal (logarithmic slope gamma' = 2.08+0.04(-0.02)) and quite flattened (axial ratio q = 0.60+0.08(-0.03)). The galaxy is mildly anisotropic (delta = 0.08 +/- 0.02) and shows a fair amount of rotational support, in particular towards the outer regions. We determine a dark matter fraction lower limit of 28 per cent within the effective radius. The stellar contribution to the total mass Distribution is close to maximal for a Chabrier initial mass Function (IMF), whereas for a Salpeter IMF the stellar mass exceeds the total mass within the galaxy inner regions. We find that the combination of a Navarro, Frenk and White dark matter halo with the maximally rescaled luminous profile provides a remarkably good fit to the total mass Distribution over a broad radial range. Our results confirm and expand the findings of the Sloan Lens ACS Survey for early-type galaxies of comparable velocity dispersion (Sigma(SDSS) = 214 +/- 11 km s-1). The internal structure of SDSS J0728 is consistent with that of local early-type galaxies of comparable velocity dispersion as measured by the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) project, suggesting lack of evolution in the past two billion years.

  • Crash-testing the CAULDRON code for joint lensing and dynamics analysis of early-type galaxies
    Monthly Notices of the Royal Astronomical Society, 2009
    Co-Authors: Matteo Barnabè, Carlo Nipoti, Léon V. E. Koopmans, S. Vegetti, Luca Ciotti
    Abstract:

    We apply the joint lensing and dynamics code for the analysis of early-type galaxies, CAULDRON, to a rotating N-body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-Integral Distribution Function. The goal is to study how CAULDRON performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N-body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density Distribution. We find that several global properties of the N-body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density Distribution. In particular, the logarithmic slope of the total density Distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true Distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ~ 10 per cent of the total mass. Unless the line of sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the V/sigma ratio, and the anisotropy parameter delta. We conclude that the CAULDRON code can be safely and effectively applied to real early-type lens galaxies, providing reliable information also for systems that depart significantly from the method's assumptions.

  • A Unifying Framework for Self-consistent Gravitational Lensing and Stellar Dynamics Analyses of Early-Type Galaxies
    The Astrophysical Journal, 2007
    Co-Authors: Matteo Barnabè, Léon V. E. Koopmans
    Abstract:

    Gravitational lensing and stellar dynamics are two independent methods, based solely on gravity, to study the mass Distributions of galaxies. Both methods suffer from degeneracies, however, that are difficult to break. In this paper, we present a new framework that self-consistently unifies gravitational lensing and stellar dynamics. This approach breaks some of classical degeneracies that have limited their individual usage, in particular in the study of high-redshift galaxies. The methodology is based on the premise that, for any given galaxy potential, the mapping of both the unknown lensed source brightness Distribution and the stellar phase-space Distribution Function on to the photometric and kinematic observables, can be cast as a single set of coupled linear equations. This set of linear equations is solved, maximizing the likelihood penalty Function. The evidence penalty Function, as derived from Bayesian statistics, subsequently allows the best potential-model parameters to be found and potential-model families, or other model assumptions (e.g. PSF), to be quantitatively ranked. We have implemented a fast algorithm that solves for the maximum-likelihood pixelized lensed source brightness Distribution and the two-Integral stellar phase-space Distribution Function f(E, L_z), assuming axisymmetric potentials. To make the method practical, we have devised a new Monte-Carlo approach to Schwarzschild's orbital superposition method, based on the superposition of two-Integral (E and L_z) toroidal components, to find the maximum-likelihood two-Integral Distribution Function in a matter of seconds in any axisymmetric potential. The non-linear parameters of the potential are subsequently found through a hybrid MCMC and Simplex optimization of the evidence. (Abridged)

David Merritt - One of the best experts on this subject based on the ideXlab platform.

  • The stellar dynamics of omega centauri.
    The Astronomical Journal, 1997
    Co-Authors: David Merritt, Georges Meylan, Michel Mayor
    Abstract:

    The stellar dynamics of ω Centauri are inferred from the radial velocities of 469 stars measured with CORAVEL (Mayor et al. 1997). Rather than fit the data to a family of models, we generate estimates of all dynamical Functions nonparametrically, by direct operation on the data. The cluster is assumed to be oblate and edge-on but mass is not assumed to follow light. The mean motions are consistent with axisymmetry but the rotation is not cylindrical. The peak rotational velocity is 7.9 km s at ∼ 11 pc from the center. The apparent rotation of ω Centauri is attributable in part to its proper motion. We reconstruct the stellar velocity ellipsoid as a Function of position, assuming isotropy in the meridional plane. We find no significant evidence for a difference between the velocity dispersions parallel and perpendicular to the meridional plane. The mass Distribution inferred from the kinematics is slightly more extended than, though not strongly inconsistent with, the luminosity Distribution. We also derive the two-Integral Distribution Function f(E,Lz) implied by the velocity data.

  • The Dynamical Inverse Problem for Axisymmetric Stellar Systems
    The Astronomical Journal, 1996
    Co-Authors: David Merritt
    Abstract:

    The standard method of modelling axisymmetric stellar systems begins from the assumption that mass follows light. The gravitational potential is then derived from the luminosity Distribution, and the unique two-Integral Distribution Function f(E,Lz) that generates the stellar density in this potential is found. It is shown that the gravitational potential can instead be generated directly from the velocity data in a two-Integral galaxy, thus allowing one to drop the assumption that mass follows light. The two-dimensional rotational velocity field can also be recovered in a model-independent way. Regularized algorithms for carrying out the inversions are presented and tested by application to pseudo-data from a family of oblate models.

Eric Emsellem - One of the best experts on this subject based on the ideXlab platform.

  • A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar
    Monthly Notices of the Royal Astronomical Society, 2003
    Co-Authors: Eric Emsellem, Paul Goudfrooij, Pierre Ferruit
    Abstract:

    TIGER Integral-field spectrography and Hubble Space Telescope Wide Field and Planetary Camera 2 (WFPC2) imaging of the E3 galaxy NGC 2974 are used to derive the kinematics of the stellar and ionized gas components in itscentral 500 pc. We derive a numerical two-Integral Distribution Function from a multi-Gaussian expansion (MGE) mass model using the Hunter & Qian formalism. The TIGER and published long-slit stellar kinematics, including higher-order moments, are well fitted with this self-consistent model, requiring neither the addition of a significant mass contribution from a hidden disc structure nor the presence of a central dark mass (at that spatial resolution). The data reveal the presence of a striking, highly contrasted, two-arm gaseous spiral structure within a radius of ∼200 pc, corresponding to a total mass of 6.8 x 10 4 solar masses of ionized gas. We use a deconvolved TIGER data cube to probe its kinematics at a resolution of about 0.35 arcsec FWHM. Strong departures from circular motions are observed, as well as high velocity dispersion values on the inner side of the arms. We interpret the observed gas morphology and kinematics as the signature of streaming gas flows driven by a ∼540-pc diameter bar with Ω p = 700 ′ 100 km s - 1 kpc - 1 . This hypothesis is strongly supported by the predictions of a density wave model. This model predicts that the bar should lie at about 35° from the line of nodes, and implies gas inflow towards the central ∼50 pc. The quadrupole perturbation due to this bar is estimated to represent less than 2 per cent of the underlying gravitational potential (a maximum torque of about 10 per cent), explaining the lack of a direct detection via broad-band photometry in the visible. Despite its weakness, the inner bar of NGC 2974 may be able to drive some gas within a 10-pc radius. We suggest that the presence of such inner bars might be more common among early-type disc galaxies than is generally thought, and that deep high-resolution emission-line imagery may be the best way to detect such structures.

  • A 60 pc counter-rotating core in NGC 4621
    Astronomy & Astrophysics, 2002
    Co-Authors: F. Wernli, Eric Emsellem, Y. Copin
    Abstract:

    We present adaptive optics assistedOASIS Integral fieldspectrography of the S0 galaxy NGC 4621. Two-dimensional stellar kinematical maps (mean velocity and dispersion) reveal the presence of a ∼60 pc diameter counter-rotating core (CRC), the smallest observed to date. TheOASIS data also suggests that the kinematic center of the CRC isslightly offset from the center of the outer isophotes. This seems to be confirmed by archival HST/STIS data. We also present the HST/WFPC2 V − I colour map, which exhibits a central elongated red structure, also slightly off-centered in the same direction as the kinematic centre. We then construct an axisymmetric model of NGC 4621: the two-Integral Distribution Function is derived using the Multi-Gaussian Expansion and the Hunter & Qian (1993) formalisms. Although the stellar velocities are reasonably fitted, including the region of the counter-rotating core, significant discrepancies between the model and the observations demonstrate the need for a more general model (e.g. a three-Integral model).

Luca Ciotti - One of the best experts on this subject based on the ideXlab platform.

  • Jeans modeling of axisymmetric galaxies with multiple stellar populations
    arXiv: Astrophysics of Galaxies, 2021
    Co-Authors: Caterina Caravita, Luca Ciotti, Silvia Pellegrini
    Abstract:

    We present the theoretical framework and the numerical setting of JASMINE2, a code designed to efficiently solve the Jeans equations for multi-component axisymmetric stellar systems. The models may include an arbitrary number of stellar Distributions, a dark matter halo, and a central supermassive black hole; each stellar Distribution is implicitly described by a two-Integral Distribution Function, and the stellar components can have different structural (density profile, flattening, mass,scale-length), dynamical (rotation, velocity dispersion anisotropy), and population (age, metallicity, initial mass Function, mass-to-light ratio) properties. In order to determine the ordered rotational velocity and the azimuthal velocity dispersion fields of each component, we introduce a decomposition that can be used when the commonly adopted Satoh decomposition cannot be applied. The numerical implementation of JASMINE2, and of the post-processing procedures (including projection), are optimised to fully exploit the scalings allowed by the Poisson and the Jeans equations. For illustrative purposes, we present three multi-component galaxy models with a central black hole and a dark matter halo; one of the models is also used to test JASMINE2 against available analytical solutions.

  • Crash-testing the CAULDRON code for joint lensing and dynamics analysis of early-type galaxies
    Monthly Notices of the Royal Astronomical Society, 2009
    Co-Authors: Matteo Barnabè, Carlo Nipoti, Léon V. E. Koopmans, S. Vegetti, Luca Ciotti
    Abstract:

    We apply the joint lensing and dynamics code for the analysis of early-type galaxies, CAULDRON, to a rotating N-body stellar system with dark matter halo which significantly violates the two major assumptions of the method, i.e. axial symmetry supported by a two-Integral Distribution Function. The goal is to study how CAULDRON performs in an extreme case, and to determine which galaxy properties can still be robustly recovered. Three data sets, corresponding to orthogonal lines of sight, are generated from the N-body system and analysed with the identical procedure followed in the study of real lens galaxies, adopting an axisymmetric power-law total density Distribution. We find that several global properties of the N-body system are recovered with remarkable accuracy, despite the fact that the adopted power-law model is too simple to account for the lack of symmetry of the true density Distribution. In particular, the logarithmic slope of the total density Distribution is robustly recovered to within less than 10 per cent (with the exception of the ill-constrained very inner regions), the inferred angle-averaged radial profile of the total mass closely follows the true Distribution, and the dark matter fraction of the system (inside the effective radius) is correctly determined within ~ 10 per cent of the total mass. Unless the line of sight direction is almost parallel to the total angular momentum vector of the system, reliably recovered quantities also include the angular momentum, the V/sigma ratio, and the anisotropy parameter delta. We conclude that the CAULDRON code can be safely and effectively applied to real early-type lens galaxies, providing reliable information also for systems that depart significantly from the method's assumptions.

  • Vertical dynamics of disk galaxies in MOND
    Monthly Notices of the Royal Astronomical Society, 2007
    Co-Authors: Carlo Nipoti, Pasquale Londrillo, Hongsheng Zhao, Luca Ciotti
    Abstract:

    We investigate the possibility of discriminating between Modified Newtonian Dynamics (MOND) and Newtonian gravity with dark matter, by studying the vertical dynamics of disk galaxies. We consider models with the same circular velocity in the equatorial plane (purely baryonic disks in MOND and the same disks in Newtonian gravity embedded in spherical dark matter haloes), and we construct their intrinsic and projected kinematical fields by solving the Jeans equations under the assumption of a two-Integral Distribution Function. We found that the vertical velocity dispersion of deep-MOND disks can be much larger than in the equivalent spherical Newtonian models. However, in the more realistic case of high-surface density disks this effect is significantly reduced, casting doubts on the possibility of discriminating between MOND and Newtonian gravity with dark matter by using current observations.