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Mass-to-light Ratio (mass-to-light + ratio)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

The disc mass of spiral galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
Paolo Salucci
ABSTRACT We derive the disc masses of 18 spiral galaxies of different luminosity and Hubble type, both by mass modelling their rotation curves and by fitting their spectral energy distribution with spectrophotometric models. The good agreement of the estimates obtained from these two different methods allows us to quantify the reliability of their performance and to derive very accurate stellar mass-to-light ratio versus colour (and stellar mass) relationships. [source]

Models of the Cosmic Horseshoe gravitational lens J1004+4112

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
S. Dye
ABSTRACT We model the extremely massive and luminous lens galaxy in the Cosmic Horseshoe Einstein ring system J1004+4112, recently discovered in the Sloan Digital Sky Survey. We use the semilinear method of Warren & Dye, which pixelizes the source surface brightness distribution, to invert the Einstein ring for sets of parametrized lens models. Here, the method is refined by exploiting Bayesian inference to optimise adaptive pixelization of the source plane and to choose between three differently parametrized models: a singular isothermal ellipsoid, a power-law model and a Navarro, Frenk & White (NFW) profile. The most probable lens model is the power law with a volume mass density ,,r,1.96±0.02 and an axis ratio of ,0.8. The mass within the Einstein ring (i.e. within a cylinder with projected distance of ,30 kpc from the centre of the lens galaxy) is (5.02 ± 0.09) × 1012 M ,, and the mass-to-light ratio is ,30. Even though the lens lies in a group of galaxies, the preferred value of the external shear is almost zero. This makes the Cosmic Horseshoe unique amongst large separation lenses, as almost all the deflection comes from a single, very massive galaxy with little boost from the environment. [source]

Mass modelling of dwarf spheroidal galaxies: the effect of unbound stars from tidal tails and the Milky Way

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007
Jaros, aw Klimentowski
ABSTRACT We study the origin and properties of the population of unbound stars in the kinematic samples of dwarf spheroidal (dSph) galaxies. For this purpose we have run a high-resolution N -body simulation of a two-component dwarf galaxy orbiting in a Milky Way potential. In agreement with the tidal stirring scenario of Mayer et al., the dwarf is placed on a highly eccentric orbit, its initial stellar component is in the form of an exponential disc and it has a NFW-like dark matter (DM) halo. After 10 Gyr of evolution the dwarf produces a spheroidal stellar component and is strongly tidally stripped so that mass follows light and the stars are on almost isotropic orbits. From this final state, we create mock kinematic data sets for 200 stars by observing the dwarf in different directions. We find that when the dwarf is observed along the tidal tails the kinematic samples are strongly contaminated by unbound stars from the tails. We also study another source of possible contamination by adding stars from the Milky Way. We demonstrate that most of the unbound stars can be removed by the method of interloper rejection proposed by den Hartog & Katgert and recently tested on simulated DM haloes. We model the cleaned-up kinematic samples using solutions of the Jeans equation with constant mass-to-light ratio (M/L) and velocity anisotropy parameter. We show that even for such a strongly stripped dwarf the Jeans analysis, when applied to cleaned samples, allows us to reproduce the mass and M/L of the dwarf with accuracy typically better than 25 per cent and almost exactly in the case when the line of sight is perpendicular to the tidal tails. The analysis was applied to the new data for the Fornax dSph galaxy. We show that after careful removal of interlopers the velocity dispersion profile of Fornax can be reproduced by a model in which mass traces light with a M/L of 11 solar units and isotropic orbits. We demonstrate that most of the contamination in the kinematic sample of Fornax probably originates from the Milky Way. [source]

The SAURON project , IV.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
The mass-to-light ratio, lenticular galaxies, the Fundamental Plane of elliptical, the virial mass estimator
ABSTRACT We investigate the well-known correlations between the dynamical mass-to-light ratio (M/L) and other global observables of elliptical (E) and lenticular (S0) galaxies. We construct two-integral Jeans and three-integral Schwarzschild dynamical models for a sample of 25 E/S0 galaxies with SAURON integral-field stellar kinematics to about one effective (half-light) radius Re. They have well-calibrated I -band Hubble Space Telescope WFPC2 and large-field ground-based photometry, accurate surface brightness fluctuation distances, and their observed kinematics is consistent with an axisymmetric intrinsic shape. All these factors result in an unprecedented accuracy in the M/L measurements. We find a tight correlation of the form (M/L) = (3.80 ± 0.14) × (,e/200 km s,1)0.84±0.07 between the M/L (in the I band) measured from the dynamical models and the luminosity-weighted second moment ,e of the LOSVD within Re. The observed rms scatter in M/L for our sample is 18 per cent, while the inferred intrinsic scatter is ,13 per cent. The (M/L),,e relation can be included in the remarkable series of tight correlations between ,e and other galaxy global observables. The comparison of the observed correlations with the predictions of the Fundamental Plane (FP), and with simple virial estimates, shows that the ,tilt' of the FP of early-type galaxies, describing the deviation of the FP from the virial relation, is almost exclusively due to a real M/L variation, while structural and orbital non-homology have a negligible effect. When the photometric parameters are determined in the ,classic' way, using growth curves, and the ,e is measured in a large aperture, the virial mass appears to be a reliable estimator of the mass in the central regions of galaxies, and can be safely used where more ,expensive' models are not feasible (e.g. in high-redshift studies). In this case the best-fitting virial relation has the form (M/L)vir= (5.0 ± 0.1) ×Re,2e/(LG), in reasonable agreement with simple theoretical predictions. We find no difference between the M/L of the galaxies in clusters and in the field. The comparison of the dynamical M/L with the (M/L)pop inferred from the analysis of the stellar population, indicates a median dark matter fraction in early-type galaxies of ,30 per cent of the total mass inside one Re, in broad agreement with previous studies, and it also shows that the stellar initial mass function varies little among different galaxies. Our results suggest a variation in M/L at constant (M/L)pop, which seems to be linked to the galaxy dynamics. We speculate that fast-rotating galaxies have lower dark matter fractions than the slow-rotating and generally more-massive ones. If correct, this would suggest a connection between the galaxy assembly history and the dark matter halo structure. The tightness of our correlation provides some evidence against cuspy nuclear dark matter profiles in galaxies. [source]

Galaxy groups in the Two-degree Field Galaxy Redshift Survey: the luminous content of the groups

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
V. R. Eke
ABSTRACT The Two-degree Field Galaxy Redshift Survey (2dFGRS) Percolation-Inferred Galaxy Group (2PIGG) catalogue of ,29 000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. It is found that a Schechter function is a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, and that the characteristic luminosity L, is slightly larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. Luminosity function results are presented in both the bJ and rF wavebands. The variation of the halo mass-to-light ratio, ,, with group size is studied in both of these wavebands. A robust trend of increasing , with increasing group luminosity is found in the 2PIGG data. Going from groups with bJ luminosities equal to 1010 h,2 L, to those 100 times more luminous, the typical bJ -band mass-to-light ratio increases by a factor of 5, whereas the rF -band mass-to-light ratio grows by a factor of 3.5. These trends agree well with the predictions of the simulations which also predict a minimum in the mass-to-light ratio on a scale roughly corresponding to the Local Group. The data indicate that if such a minimum exists, then it must occur at L, 1010h,2 L,, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bJ mass-to-light ratios of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data, the mean bJ luminosity density of the Universe yields an estimate of ,m= 0.26 ± 0.03 (statistical error only). Various possible sources of systematic error are considered, with the conclusion that these could affect the estimate of ,m by a few tens of per cent. [source]

Populating dark matter haloes with galaxies: comparing the 2dFGRS with mock galaxy redshift surveys

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004
Xiaohu Yang
ABSTRACT In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as a function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N -body simulations of the standard ,CDM cosmology with ,m= 0.3, ,,= 0.7 and ,8= 0.9. Stacking simulation boxes of 100 h,1 Mpc and 300 h,1 Mpc with 5123 particles each we construct mock galaxy redshift surveys out to a redshift of z= 0.2 with a numerical resolution that guarantees completeness down to 0.01L*. We use these mock surveys to investigate various clustering statistics. The predicted two-dimensional correlation function ,(rp, ,) reveals clear signatures of redshift space distortions. The projected correlation functions for galaxies with different luminosities and types, derived from ,(rp, ,), match the observations well on scales larger than ,3 h,1 Mpc. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Modelling the ,finger-of-God' effect on small scales reveals that the standard ,CDM model predicts pairwise velocity dispersions (PVD) that are ,400 km s,1 too high at projected pair separations of ,1 h,1 Mpc. A strong velocity bias in massive haloes, with bvel,,gal/,dm, 0.6 (where ,gal and ,dm are the velocity dispersions of galaxies and dark matter particles, respectively) can reduce the predicted PVD to the observed level, but does not help to resolve the overprediction of clustering power on small scales. Consistent results can be obtained within the standard ,CDM model only when the average mass-to-light ratio of clusters is of the order of 1000 (M/L), in the B -band. Alternatively, as we show by a simple approximation, a ,CDM model with ,8, 0.75 may also reproduce the observational results. We discuss our results in light of the recent WMAP results and the constraints on ,8 obtained independently from other observations. [source]

Velocity dispersions of dwarf spheroidal galaxies: dark matter versus MOND

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001
Ewa L.
We present predictions for the line-of-sight velocity dispersion profiles of dwarf spheroidal galaxies and compare them to observations in the case of the Fornax dwarf. The predictions are made in the framework of standard dynamical theory of spherical systems with different velocity distributions. The stars are assumed to be distributed according to Sérsic laws with parameters fitted to observations. We compare predictions obtained assuming the presence of dark matter haloes (with density profiles adopted from N -body simulations) with those resulting from Modified Newtonian Dynamics (MOND). If the anisotropy of velocity distribution is treated as a free parameter, observational data for Fornax are reproduced equally well by models with dark matter and with MOND. If stellar mass-to-light ratio of 1 M,/L, is assumed, the required mass of the dark halo is , two orders of magnitude larger than the mass in stars. The derived MOND acceleration scale is . In both cases a certain amount of tangential anisotropy in the velocity distribution is needed to reproduce the shape of the velocity dispersion profile in Fornax. [source]

The Tully,Fisher relation and its implications for the halo density profile and self-interacting dark matter

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
H. J. Mo
We show that the Tully,Fisher relation observed for spiral galaxies can be explained in the current scenario of galaxy formation without invoking subtle assumptions, provided that galactic-sized dark haloes have low concentrations which do not change significantly with halo circular velocity. This conclusion does not depend significantly on whether haloes have cuspy or flat profiles in the inner region. In such a system, both the disc and the halo may contribute significantly to the maximum rotation of the disc, and the gravitational interaction between the disc and halo components leads to a tight relation between the disc mass and maximum rotation velocity. The model can therefore be tested by studying the Tully,Fisher zero points for galaxies with different disc mass-to-light ratios. With model parameters (such as the ratio between disc and halo mass, the specific angular momentum of disc material, disc formation time) chosen in plausible ranges, the model can well accommodate the zero-point, slope and scatter of the observed Tully,Fisher relation, as well as the observed large range of disc surface densities and sizes. In particular, the model predicts that low surface brightness disc galaxies obey a Tully,Fisher relation very similar to that of normal discs, if the disc mass-to-light ratio is properly taken into account. About half of the gravitational force at maximum rotation comes from the disc component for normal discs, while the disc contribution is lower for galaxies with a lower surface density. The halo profile required by the Tully,Fisher relation is as concentrated as that required by the observed rotation curves of faint discs, but less concentrated than that given by current simulations of cold dark matter (CDM) models. We discuss the implication of such profiles for structure formation in the Universe and for the properties of dark matter. Our results cannot be explained by some of the recent proposals for resolving the conflict between conventional CDM models and the observed rotation-curve shapes of faint galaxies. If dark matter self-interaction (either scattering or annihilation) is responsible for the shallow profile, the observed Tully,Fisher relation requires the interaction cross-section ,X to satisfy ,,X|v|,/mX,10,16 cm3 s,1 GeV,1, where mX is the mass of a dark matter particle. [source]

The nature of galaxy bias and clustering

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2000
A. J. Benson
We have used a combination of high resolution cosmological N -body simulations and semi-analytic modelling of galaxy formation to investigate the processes that determine the spatial distribution of galaxies in cold dark matter (CDM) models and its relation to the spatial distribution of dark matter. The galaxy distribution depends sensitively on the efficiency with which galaxies form in haloes of different mass. In small mass haloes, galaxy formation is inhibited by the reheating of cooled gas by feedback processes, whereas in large mass haloes, it is inhibited by the long cooling time of the gas. As a result, the mass-to-light ratio of haloes has a deep minimum at the halo mass, ,1012 M,, associated with L* galaxies, where galaxy formation is most efficient. This dependence of galaxy formation efficiency on halo mass leads to a scale-dependent bias in the distribution of galaxies relative to the distribution of mass. On large scales, the bias in the galaxy distribution is related in a simple way to the bias in the distribution of massive haloes. On small scales, the correlation function is determined by the interplay between various effects including the spatial exclusion of dark matter haloes, the distribution function of the number of galaxies occupying a single dark matter halo and, to a lesser extent, dynamical friction. Remarkably, these processes conspire to produce a correlation function in a flat, ,0=0.3, CDM model that is close to a power law over nearly four orders of magnitude in amplitude. This model agrees well with the correlation function of galaxies measured in the automated-plate measurement survey. On small scales, the model galaxies are less strongly clustered than the dark matter, whereas on large scales they trace the occupied haloes. Our clustering predictions are robust to changes in the parameters of the galaxy formation model, provided only those models which match the bright end of the galaxy luminosity function are considered. [source]

Dynamical modelling of luminous and dark matter in 17 Coma early-type galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
J. Thomas
ABSTRACT Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB=,18.79 and ,22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1,4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10,50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss,Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations. [source]

Axisymmetric orbit models of N -body merger remnants: a dependency of reconstructed mass on viewing angle

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
J. Thomas
ABSTRACT We model mock observations of collisionless N -body disc,disc mergers with the same axisymmetric orbit superposition program that has been used to model elliptical galaxies in Coma. The remnants sample representatively the shape distribution of disc,disc mergers, including the most extreme cases, like highly prolate, maximally triaxial and dominantly oblate objects. The aim of our study is to better understand how the assumption of axial symmetry affects reconstructed masses and stellar motions of systems which are intrinsically not axisymmetric, whether the axisymmetry assumption then leads to a bias and how such a potential bias can be recognized in models of real galaxies. The mass recovery at the half-light radius depends on viewing angle and intrinsic shape: edge-on views allow to reconstruct total masses with an accuracy between 20 per cent (triaxial/prolate remnants) and 3 per cent (oblate remnant). Masses of highly flattened, face-on systems are underestimated by up to 50 per cent. Deviations in local mass densities can be larger where remnants are strongly triaxial or prolate. Luminous mass-to-light ratios are sensitive to box orbits in the remnants. Box orbits cause the central value of the Gauss,Hermite parameter H4 to vary with viewing angle. Reconstructed luminous mass-to-light ratios, as well as reconstructed central masses, follow this variation. Luminous mass-to-light ratios are always underestimated (up to a factor of 2.5). Respective dark haloes in the models can be overestimated by about the same amount, depending again on viewing angle. Reconstructed velocity anisotropies , depend on viewing angle as well as on the orbital composition of the remnant and are mostly accurate to about ,,= 0.2. Larger deviations can occur towards the centre or the outer regions, respectively. We construct N -body realizations of the Schwarzschild models to discuss chaotic orbits and the virial equilibrium in our models. In this study we explore the extreme limits of axisymmetric models. Apparently flattened, rotating ellipticals of intermediate mass are likely close to both, axial symmetry and edge-on orientation. Our results imply that Schwarzschild models allow a reconstruction of their masses and stellar anisotropies with high accuracy. [source]

The kinematical structure of gravitationally lensed arcs

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Ole Möller
ABSTRACT In this paper, the expected properties of the velocity fields of strongly lensed arcs behind galaxy clusters are investigated. The velocity profile along typical lensed arcs is determined by ray-tracing light rays from a model source galaxy through parametric cluster toy models consisting of individual galaxies embedded in a dark cluster halo. We find that strongly lensed arcs of high-redshift galaxies show complex velocity structures that are sensitive to the details of the mass distribution within the cluster, in particular at small scales. From fits to the simulated imaging and kinematic data, we demonstrate that reconstruction of the source velocity field is in principle feasible. Two-dimensional kinematic information obtained with integral field units on large ground-based telescopes in combination with adaptive optics will allow the reconstruction of rotation curves of lensed high redshift galaxies. This makes it possible to determine the mass-to-light ratios of galaxies at redshifts z > 1 out to about 2,3 scalelengths with better than ,20 per cent accuracy. We also discuss the possibilities of using two-dimensional kinematic information along the arcs to give additional constraints on the cluster lens mass models. [source]

Galaxy groups in the Two-degree Field Galaxy Redshift Survey: the luminous content of the groups

The three-dimensional power spectrum of dark and luminous matter from the VIRMOS-DESCART cosmic shear survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003
Ue-Li Pen
ABSTRACT We present the first optimal power spectrum estimation and three-dimensional deprojections for the dark and luminous matter and their cross-correlations. The results are obtained using a new optimal fast estimator, deprojected using minimum variance and Singular Value Decomposition (SVD) techniques. We show the resulting 3D power spectra for dark matter and galaxies, and their covariance for the VIRMOS-DESCART weak lensing shear and galaxy data. The survey is most sensitive to non-linear scales kNL, 1 h Mpc,1. On these scales, our 3D power spectrum of dark matter is in good agreement with the RCS 3D power spectrum found by Tegmark & Zaldarriaga. Our galaxy power is similar to that found by the 2MASS survey, and larger than that of SDSS, APM and RCS, consistent with the expected difference in galaxy population. We find an average bias b= 1.24 ± 0.18 for the I -selected galaxies, and a cross-correlation coefficient r= 0.75 ± 0.23. Together with the power spectra, these results optimally encode the entire two point information about dark matter and galaxies, including galaxy,galaxy lensing. We address some of the implications regarding galaxy haloes and mass-to-light ratios. The best-fitting ,halo' parameter h,r/b= 0.57 ± 0.16, suggesting that dynamical masses estimated using galaxies systematically underestimate total mass. Ongoing surveys, such as the Canada,France,Hawaii Telescope Legacy Survey, will significantly improve on the dynamic range, and future photometric redshift catalogues will allow tomography along the same principles. [source]

The Tully,Fisher relation and its implications for the halo density profile and self-interacting dark matter

Smooth, undisturbed dwarf spheroidal galaxies in the Perseus cluster core: Implications for dark matter content

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
Sj. Penny
Abstract Using deep HST/ACS observations of the core of the Perseus Cluster, we identify a large population of dwarf elliptical galaxies down to MV = ,12. All these dwarfs are remarkably smooth in appearance, showing no evidence for internal features that could be the result of tidal processes or star formation induced by the cluster potential. Based on these observations and the relatively large sizes of these dwarfs, we argue that at least some must have a large dark matter component to prevent their disruption by the cluster potential. We further derive a new method to quantify the dark matter content of cluster dSphs without the use of kinematics, which are impossible to obtain at these distances. We find that mass-to-light ratios for dwarfs in the core of the Perseus Cluster are comparable to those found for Local Group dSphs, ranging between M,/L, , 1 and 120. This is evidence that dwarf spheroidals reside in dark matter subhalos that protect them from tidal processes in the cores of dense clusters (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]