Showing papers by "Tommaso Treu published in 2003"

Constraints on the equation of state of dark energy and the Hubble constant from stellar ages and the CMB

Abstract: We place tight constraints on the redshift-averaged, effective value of the equation of state of dark energy, w, using only the absolute ages of Galactic stars and the observed position of the first peak in the angular power spectrum of the CMB. We find w -1, this finding suggests that within our uncertainties, dark energy is indistinguishable from a classical vacuum energy term. We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0 from SDSS galaxies and obtain an independent estimate for the Hubble constant, H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2 does not yield, currently, a precise determination of w(z), but shows that the age--redshift relation is consistent with a Standard LCDM universe with $w=-1$.

A Wide-Field Hubble Space Telescope Study of the Cluster Cl 0024+16 at z = 0.4. I. Morphological Distributions to 5 Mpc Radius

Abstract: We describe a new wide-field Hubble Space Telescope survey of the galaxy cluster Cl 0024+16 (z ≈ 0.4) consisting of a sparsely sampled mosaic of 39 Wide Field Planetary Camera 2 images that extends to a cluster radius of ~5 Mpc. Together with extensive ground-based spectroscopy taken from the literature, augmented with over a hundred newly determined redshifts, this unique data set enables us to examine environmental influences on the properties of cluster members from the inner core to well beyond the virial radius (~1.7 Mpc). We catalog photometric measures for 22,000 objects to I 25 and assign morphological types for 2181 to I = 22.5, of which 195 are spectroscopically confirmed cluster members. We examine both the morphology-radius (T-R) and morphology-density (T-Σ) relations and demonstrate sensitivities adequate for measures from the core to a radius of ~5 Mpc, spanning over 3 decades in local projected density. The fraction of early-type galaxies declines steeply from the cluster center to 1 Mpc radius and more gradually thereafter, asymptoting toward the field value at the periphery. We discuss our results in the context of three distinct cluster zones, defined according to different physical processes that may be effective in transforming galaxy morphology in each. By treating infalling galaxies as isolated test particles, we deduce that the most likely processes responsible for the mild gradient in the morphological mix outside the virial radius are harassment and starvation. Although more data are needed to pin down the exact mechanisms, starvation seems more promising in that it would naturally explain the stellar and dynamical homogeneity of cluster E/S0s. However, we find significant scatter in the local density at any given radius outside ~0.5 Mpc and that the same T-Σ relation holds in subregions of the cluster, independent of location. In this hitherto unprobed region, where the potential of the cluster is weak, galaxies apparently retain their identities as members of infalling subgroups whose characteristic morphological properties remain intact. Only upon arrival in the central regions is the substructure erased, as indicated by the tight correlation between cluster radius and Σ.

Constraints on the Equation of State of Dark Energy and the Hubble Constant from Stellar Ages and the Cosmic Microwave Background

Abstract: We place constraints on the redshift-averaged, effective value of the equation of state of dark energy, w, using only the absolute ages of Galactic stars and the observed position of the first peak in the angular power spectrum of the cosmic microwave background (CMB). We find w 0.2 does not yield, currently, a precise determination of w(z), but shows that the age-redshift relation is consistent with a standard ?CDM universe with w = -1.

A wide field Hubble Space Telescope study of the cluster CL0024+16 at z=0.4. I: morphological distributions to 5 Mpc radius

Abstract: We describe a new wide field Hubble Space Telescope survey of the galaxy cluster Cl0024+16 (z~0.4) consisting of a sparse-sampled mosaic of 39 Wide Field and Planetary Camera 2 images which extends to a cluster radius of 5 Mpc. [Abridged] We examine both the morphology-radius (T-R) and morphology-density (T-Sigma) relations and demonstrate sensitivities adequate for measures from the core to a radius of 5 Mpc, spanning over 3 decades in local projected density. The fraction of early-type galaxies declines steeply from the cluster center to 1 Mpc radius and more gradually thereafter, asymptoting towards the field value at the periphery. We discuss our results in the context of three distinct cluster zones, defined according to different physical processes that may be effective in transforming galaxy morphology in each. By treating infalling galaxies as isolated test particles, we deduce that the most likely processes responsible for the mild gradient in the morphological mix outside the virial radius are harassment and starvation. Although more data are needed to pin down the exact mechanisms, starvation seems more promising in that it would naturally explain the stellar and dynamical homogeneity of cluster E/S0s. However, we find significant scatter in the local density at any given radius outside 0.5 Mpc, and that the same T-Sigma relation holds in subregions of the cluster, independent of location. In this hitherto unprobed region, where the potential of the cluster is weak, galaxies apparently retain their identities as members of infalling sub-groups whose characteristic morphological properties remain intact. Only upon arrival in the central regions is the substructure erased, as indicated by the tight correlation between cluster radius and Sigma.

A Wide-Field Hubble Space Telescope Study of the Cluster Cl 0024+1654 at z=0.4. II. The Cluster Mass Distribution

Abstract: We present a comprehensive lensing analysis of the rich cluster Cl0024+1654 (z=0.395) based on panoramic sparse-sampled imaging conducted with the WFPC2 and STIS cameras on board the Hubble Space Telescope. By comparing higher fidelity signals in the limited STIS data with the wider field data available from WFPC2, we demonstrate an ability to detect reliably weak lensing signals to a cluster radius of ≃5 h −1 65 Mpc where the mean shear is around 1%. This enables us to study the distribution of dark matter with respect to the cluster light over an unprecedented range of cluster radius and environments. The projected mass distribution reveals a secondary concentration representing 30% of the overall cluster mass, which is also visible in the distribution of cluster member galaxies. We develop a method to derive the projected mass profile of the main cluster taking into account the influence of the secondary clump. We normalize the mass profile determined from the shear by assuming that background galaxies selected with 23 2.4. An isothermal mass profile is therefore strongly rejected, whereas a NFW profile with M200= 6.1 +1.2 1.1 10 14 h −1 65 M⊙ provides a good fit to the lensing data. We isolate cluster members according to their optical-near infrared colors; the red cluster light closely traces the dark matter with a mean mass-to-light ratio of M/LK= 40±5 h65 M⊙/L⊙. Similar profiles for mass and light on 1-5 Mpc scales are expected if cluster assembly is largely governed by infalling groups. Subject headings: cosmology: observations — gravitational lensing — cluster of galaxies: individual (Cl 0024+1654)

The structure and dynamics of luminous and dark matter in the early-type lens galaxy of 0047-281 at z=0.485

Abstract: We have measured the kinematic profile of the early-type (E/S0) lens galaxy in the system 0047-281 (z = 0.485) with the Echelle Spectrograph and Imager (ESI) on the W. M. Keck II Telescope, as part of the Lenses Structure and Dynamics (LSD) Survey. The central velocity dispersion is ? = 229 ? 15 km s-1, and the dispersion profile is nearly flat to beyond one effective radius (Re). No significant streaming motion is found. Surface photometry of the lens galaxy is measured from Hubble Space Telescope images. From the offset from the local fundamental plane (FP), we measure an evolution of the effective mass-to-light ratio (M/L) of ? log = -0.37 ? 0.06 between z = 0 and 0.485, consistent with the observed evolution of field E/S0 galaxies. (We assume h65 = 1, ?m = 0.3, and ?? = 0.7 throughout.) Gravitational lens models provide a mass of ME = ? 1011 h M? inside the Einstein radius of RE = h kpc. This allows us to break the degeneracy between velocity anisotropy and density profile typical of dynamical models for E/S0 galaxies. We find that constant-M/L models, even with strongly tangential anisotropy of the stellar velocity ellipsoid, are excluded at more than 99.9% CL. The total mass distribution inside RE can be described by a single power-law density profile, ?t r, with an effective slope ?' = 1.90 (68% CL; ?0.1 systematic error). Two-component models yield an upper limit (68% CL) of ? ? 1.55 on the power-law slope of the dark matter density profile and a projected dark matter mass fraction of 0.41(0.54)() (68% CL) inside RE, for Osipkov-Merritt models with anisotropy radius ri = ? . The stellar M*/L values derived from the FP agree well with the maximum allowed value from the isotropic dynamical models (i.e., the maximum-bulge solution). The fact that both lens systems 0047-281 (z = 0.485) and MG 2016+112 (z = 1.004) are well described inside their Einstein radii by a constant-M*/L stellar mass distribution embedded in a nearly logarithmic potential?with an isotropic or a mildly radially anisotropic dispersion tensor?could indicate that E/S0 galaxies underwent little structural evolution at z 1 and have a close-to-isothermal total mass distribution in their inner regions. Whether this conclusion can be generalized, however, requires the analysis of more systems. We briefly discuss our results in the context of E/S0 galaxy formation and cold dark matter simulations.

A Wide Field Hubble Space Telescope Study of the Cluster Cl0024+1654 at z=0.4 II: The Cluster Mass Distribution

Abstract: (abridged) We present a comprehensive lensing analysis of the rich cluster Cl0024+1654 based on panoramic sparse-sampled imaging conducted with HST. We demonstrate an ability to detect reliably weak lensing signals to a cluster radius of ~5 Mpc where the mean shear is around 1%. The projected mass distribution reveals a secondary concentration representing 30% of the overall cluster mass, which is also visible in the distribution of cluster member galaxies. We normalize the mass profile determined from the shear by assuming that background galaxies selected with I=23-26 have a redshift distribution statistically similar to that in the HDFs. Combining strong and weak constraints, we are able to probe the mass profile of the cluster on scales of 0.1 to 5 Mpc thus providing a valuable test of the universal form proposed by NFW on large scales. A generalized power law fit indicates a asymptotic density distribution with 3D slope larger than 2.4. An isothermal mass profile is therefore strongly rejected, whereas a NFW profile with M_200= 6.1+/-1 10^14 M_sun provides a good fit to the lensing data. We isolate cluster members according to their optical-near infrared colors; the red cluster light closely traces the dark matter with a mean mass-to-light ratio of M/L_K~ 40 M/L_sun. Similar profiles for mass and light on 1-5 Mpc scales are expected if cluster assembly is largely governed by infalling groups.

The Dark Matter Distribution in the Central Regions of Galaxy Clusters

Abstract: Cosmological N-body simulations predict that dark matter halos should have a universal shape characterized by a steep, cuspy inner profile. Here we report on a spectroscopic study of six clusters each containing a dominant brightest cluster galaxy (BCG) with nearby gravitational arcs. Three clusters have both radial and tangential gravitational arcs, whereas the other three display only tangential arcs. We analyze stellar velocity dispersion data for the BCGs in conjunction with the arc redshifts and lens models to constrain the dark and baryonic mass profiles jointly. For those clusters with radial gravitational arcs we were able to measure precisely the inner slope of the dark matter halo and compare it withthat predicted from CDM simulations.

The Hubble Constant from the Gravitational Lens B1608+656

Abstract: We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (1) the three independent time delays and flux ratios from Very Large Array observations, (2) the radio-image positions from Very Large Baseline Array observations, (3) the shape of the deconvolved Einstein ring from optical and infrared Hubble Space Telescope images, (4) the extinction-corrected lens-galaxy centroids and structural parameters, and (5) a stellar velocity dispersion, σap = 247 ± 35 km s-1, of the primary lens galaxy (G1), obtained from an echelle spectrum taken with the Keck II Telescope. The lens-mass model consists of two elliptical mass distributions with power-law density profiles and an external shear, totaling 22 free parameters, including the density slopes that are the key parameters for determining the value of H0 from lens time delays. This has required the development of a new lens code that is highly optimized for speed. The minimum-χ2 model reproduces all observations very well, including the stellar velocity dispersion and the shape of the Einstein ring. A combined gravitational lens and stellar dynamical analysis leads to a value of the Hubble constant of H0 = 75 km s- 1 Mpc -1 (68% CL; Ωm = 0.3, ΩΛ = 0.7). The nonlinear error analysis includes correlations between all free parameters, in particular the density slopes of G1 and G2, yielding an accurate determination of the random error on H0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy (G2) and has a mass density slope of γ = 2.03 ± 0.03 (68% CL) for ρ ∝ r, very close to isothermal (γ' = 2). After extinction correction, G1 exhibits a smooth surface brightness distribution with an R1/4 profile and no apparent evidence for tidal disruption by interactions with G2. Given the scope of the observational constraints and the gravitational lens models, as well as the careful corrections to the data, we believe this value of H0 to be little affected by known systematic errors (5%).

HST imaging and Keck Spectroscopy of z~6 I-band Drop-Out Galaxies in the ACS GOODS Fields

Abstract: We measure the surface density of i'-band dropout galaxies at z~6 through wide field HST/ACS imaging and ultra-deep Keck/DEIMOS spectroscopy. Using deep HST/ACS SDSS-i' (F775W) and SDSS-z' (F850LP) imaging from GOODS-N (200 arcmin^2), we identify 9 i'-drops satisfying an (i'-z')_AB>1.5 selection criterion to a depth of z'_AB=25.6 (corresponding to L*_UV at z~3-4). We use HK' imaging data to improve the fidelity of our sample, discriminating against lower redshift red galaxies and cool Galactic stars. Three i'-drops are consistent with M/L/T dwarf stars. We present ultra-deep Keck/DEIMOS spectroscopy of 10 objects from our combined GOODS-N and GOODS-S i'-drop sample. We detect Lyman-alpha emission at z=5.83 from one object in the GOODS-S field, which lies only 8arcmin away (i.e. 3Mpc/h_70) from the z=5.78 object already confirmed by Bunker et al. (2003). One possible Lyman-alpha emitter at z=6.24 is found in the GOODS-N field (although identification of this spatially-offset emission line is ambiguous). Using the rest-frame UV continuum from our 6 candidate z~6 galaxies from the GOODS-N field, we determine a lower limit to the unobscured volume-averaged global star formation rate at z~6 of (5.4+/-2.2)x10^-4 h_70 M_sun/yr/Mpc^3. We find that the cosmic star formation density in galaxies with unobscured star formation rates 15M_sun/yr/h_70^2 falls by a factor of 8 between z~3 and z~6. Hence the luminosity function of LBGs must evolve in this redshift interval: a constant integrated star formation density at $z>3$ requires a much steeper faint-end slope, or a brighter characteristic luminosity. This result is in agreement with our previous measurement from the Chandra Deep Field South (Stanway et al. 2003), indicating that cosmic variance is not a dominant source of uncertainty.

Galactic cannibalism in the galaxy cluster c0337-2522 at z=0.59

Abstract: According to the galactic cannibalism model, cD galaxies are formed in the centre of galaxy clusters by merging of massive galaxies and accretion of smaller stellar systems; however, observational examples of the initial phases of this process are lacking. We have identified a strong candidate for this early stage of cD galaxy formation: a group of five elliptical galaxies in the core of the X-ray cluster C0337-2522 at redshift z = 0.59. With the aid of numerical simulations, in which the galaxies are represented by N-body systems, we study their dynamical evolution up to z = 0; the cluster dark matter distribution is also described as an N-body system. We explore the hypothesis that some of the five galaxies will have merged before z = 0, making reasonable assumptions on the structural and dynamical characteristics of the cluster. We then compare the properties of the merger remnant with those of real ellipticals (such as its accordance with the fundamental plane, the Faber–Jackson and the MBH–σ0 relations) and, in particular, we check whether the remnant has the surface brightness profile typical of cD galaxies. We find that a multiple merging event in the considered group of galaxies will take place before z = 0 and that the merger remnant preserves the fundamental plane and the Faber–Jackson relations, while its behaviour with respect to the MBH–σ0 relation is quite sensitive to the details of black hole merging. However, the end-products of our simulations are more similar to a ‘normal’ giant elliptical than to a cD galaxy with its characteristic diffuse luminous halo, thus confirming previous indications that the formation of cD galaxies is not a necessary consequence of galaxy merging at the cluster centre.

The redshift of the Einstein ring in MG 1549+305

Abstract: A deep spectrum taken with the Echelle Spectrograph and Imager (ESI) at the Keck II Telescope as part of the Lenses Structure and Dynamics (LSD) Survey reveals the redshifts of the extremely red source of the radio Einstein ring in the gravitational lens system MG 1549+305 (zs= 1.170 +/- 0.001) and an intermediate-redshift lensed spiral galaxy (zG2= 0.604 +/- 0.001). The source redshift allows us to determine the mass of the SB0 lens galaxy enclosed by the Einstein radius (RE= 1.15 +/- 0.05 arcsec): ME≡M(

Redshift of the Einstein Ring in MG1549+305

Abstract: A deep spectrum taken with the Echelle Spectrograph and Imager (ESI) at the Keck II Telescope as part of the Lenses Structure and Dynamics (LSD) Survey reveals the redshifts of the extremely red source of the radio Einstein Ring in the gravitational lens system MG1549+305 ($z_{\rm s}=1.170\pm 0.001$) and an intermediate redshift lensed spiral galaxy ($z_{\rm G2}=0.604\pm 0.001$). The source redshift allows us to determine the mass of the SB0 lens galaxy enclosed by the Einstein Radius ($R_{\rm E}=1\farcs15\pm0\farcs05$) $M_{\rm E}$$\equiv$$M(

A Unique Small-Scale Gravitational Arc in A1201*

Abstract: We present a snapshot Hubble Space Telescope (HST) image of the galaxy cluster A1201 (z = 0.169), revealing a tangential arc 2'' from the brightest cluster galaxy (BCG). Keck Echelle Spectrograph and Imager (ESI) spectroscopy confirms that the arc is gravitational in nature and that the source galaxy lies at z = 0.451. We construct a model of the gravitational potential of the cluster that faithfully reproduces the observed arc morphology. Despite the relaxed appearance of the cluster in the HST frame, the best-fit ellipticity of the total matter distribution is total ≥ 0.5, in contrast to the light distribution of the BCG (BCG = 0.23 ± 0.03) on 2'' scales. Further deep optical observations and pointed X-ray spectro-imaging observations with Chandra are required to determine whether this elongation is due to a single elongated dark matter halo or a more complex distribution of matter in the cluster core. We compare the arc with a sample drawn from the published literature and confirm that it is unique among tangential systems in the small physical scales that it probes (~6 kpc). In anticipation of a more thorough investigation of this cluster across a broad range of physical scales, we use our fiducial lens model to estimate the projected mass and mass-to-light ratio of the cluster within a radius of 6 kpc, obtaining M = (5.9) × 1011 M☉, M/LV = 9.4 (M/L)☉. Overall our results confirm the importance of HST snapshot surveys for identifying rare lensing constraints on cluster mass distributions. In combination with follow-up optical and X-ray observations, the arc in A1201 should help to increase our understanding of the physics of cluster cores.

A unique small-scale gravitational arc in Abell 1201

Abstract: We present a snapshot Hubble Space Telescope (HST) image of the galaxy cluster A1201 (z=0.169), revealing a tangential arc 2arcsec from the brightest cluster galaxy (BCG). Keck-ESI spectroscopy confirms that the arc is gravitational in nature and that the source galaxy lies at z=0.451. We construct a model of the gravitational potential of the cluster that faithfully reproduces the observed arc morphology. Despite the relaxed appearance of the cluster in the HST frame, the best fit ellipticity of the total matter distribution is epsilon_total>0.5, in contrast to the light distribution of the BCG epsilon_BCG=0.23+/-0.03 on 2'' scales. Further deep optical observations and pointed X-ray spectro-imaging observations with Chandra are required to determine whether this elongation is due to a single elongated dark matter halo, or a more complex distribution of matter in the cluster core. We compare the arc with a sample drawn from the published literature, and confirm that it is unique among tangential systems in the small physical scales that it probes (6kpc). In anticipation of a more thorough investigation of this cluster across a broad range of physical scales, we use our fiducial lens model to estimate the projected mass and mass-to-light ratio of the cluster within a radius of 6kpc, obtaining: M=(5.9^+0.9_-0.7)x10^11 M_o, M/L_V=9.4^+2.4_-2.1(M/L)_o. Overall our results confirm the importance of HST snapshot surveys for identifying rare lensing constraints on cluster mass distributions. In combination with follow--up optical and X-ray observations, the arc in A1201 should help to increase our understanding of the physics of cluster cores.

The Dark Matter Distribution in the Central Regions of Galaxy Clusters

Abstract: Cosmological N-body simulations predict that dark matter halos should have a universal shape characterized by a steep, cuspy inner profile. Here we report on a spectroscopic study of six clusters each containing a dominant brightest cluster galaxy (BCG) with nearby gravitational arcs. Three clusters have both radial and tangential gravitational arcs, whereas the other three display only tangential arcs. We analyze stellar velocity dispersion data for the BCGs in conjunction with the arc redshifts and lens models to constrain the dark and baryonic mass profiles jointly. For those clusters with radial gravitational arcs we were able to measure precisely the inner slope of the dark matter halo and compare it with that predicted from CDM simulations.

The Dark Matter Distribution in the Central Regions of Galaxy Clusters: Implications for CDM

Abstract: We have undertaken a spectroscopic survey of gravitational arcs in a carefully chosen sample of six clusters each containing a dominant brightest cluster galaxy. We use these systems to study the relative distributions of dark and baryonic material in the central regions. Three clusters present both radial and tangential arcs and provide particularly strong constraints on the mass profiles, whereas the other three display only tangential arcs and act as a control set. We analyze stellar velocity dispersion data for the brightest cluster galaxies in conjunction with the arc redshifts and lens models to constrain the dark and baryonic mass profiles jointly. For the systems containing radial arcs we find that the inner dark matter density profile is consistent with a 3-D distribution, rho_{DM} propto r^-beta, with logarithmic slope =0.52^{+0.05}_{-0.05} (68% CL). Similarly, we find that the tangential arc sample gives an upper limit, beta 99% confidence. In addition, we find considerable cosmic scatter in the beta (Delta beta ~0.3) values of the radial arc sample. We find no evidence that systems with radial arcs preferentially yield flatter dark matter profiles as might be expected if they were a biased subset. We discuss the validity of our 1-D mass reconstruction method and verify its conclusions by comparing with results of a more rigorous ray-tracing lensing code. Our results extend and strengthen the earlier conclusions presented by Sand et al. (2002) and suggest the relationship between dark and visible matter in the cores of clusters is more complex than anticipated from recent simulations. (abridged)

The Hubble Constant from the Gravitational Lens B1608+656

Abstract: We present a refined gravitational lens model of the four-image lens system B1608+656 based on new and improved observational constraints: (i) the three independent time-delays and flux-ratios from VLA observations, (ii) the radio-image positions from VLBA observations, (iii) the shape of the deconvolved Einstein Ring from optical and infrared HST images, (iv) the extinction-corrected lens-galaxy centroids and structural parameters, and (v) a stellar velocity dispersion, sigma_ap=247+-35 km/s, of the primary lens galaxy (G1), obtained from an echelle spectrum taken with the Keck--II telescope. The lens mass model consists of two elliptical mass distributions with power-law density profiles and an external shear, totaling 22 free parameters, including the density slopes which are the key parameters to determine the value of H_0 from lens time delays. This has required the development of a new lens code that is highly optimized for speed. The minimum-chi^2 model reproduces all observations very well, including the stellar velocity dispersion and the shape of the Einstein Ring. A combined gravitational-lens and stellar dynamical analysis leads to a value of the Hubble Constant of H_0=75(+7/-6) km/s/Mpc (68 percent CL; Omega_m=0.3, Omega_Lambda=0.7. The non-linear error analysis includes correlations between all free parameters, in particular the density slopes of G1 and G2, yielding an accurate determination of the random error on H_0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy (G2), and has a mass density slope of gamma_G1=2.03(+0.14/-0.14) +- 0.03 (68 percent CL) for rho~r^-gamma', very close to isothermal (gamma'=2). (Abridged)

The Formation of Early-Type Galaxies: Observations to z=1

Abstract: How does the number density of early-type galaxies (E+S0) evolve with redshift? What are their star formation histories? Do their mass density profile and other structural properties evolve with redshift? Answering these questions is key to understanding how E+S0s form and evolve. I review the observational evidence on these issues, focusing on the redshift range z=0.1-1, and compare it to the predictions of current models of galaxy formation.

The dark matter halos of spheroidal galaxies and clusters of galaxies

Abstract: We describe the first results from two observational projects aimed at measuring the amount and spatial distribution of dark matter in distant early-type galaxies (E/S0s) and clusters of galaxies. At the galaxy scale, the Lenses Structure and Dynamics (LSD) Survey is gathering kinematic data for distant (up to $z\sim1$) E/S0s that are gravitational lenses. A joint lensing and dynamical analysis constrains the fraction of dark matter within the Einstein radius, the mass-to-light ratio of the stellar component, and the total slope of the mass density profile. These properties and their evolution with redshift are briefly discussed in terms of the formation and evolution of E/S0 galaxies and measurement of the Hubble Constant from gravitational time delay systems. At the cluster scale -- after careful removal of the stellar component with a joint lensing and dynamical analysis -- systems with giant radial arcs can be used to measure precisely the inner slope of the dark matter halo. An HST search for radial arcs and the analysis of a first sample are briefly discussed in terms of the universal dark matter halos predicted by CDM simulations.

The Lenses Structure & Dynamics Survey: The internal structure and evolution of E/S0 galaxies and the determination of H_0 from time-delay systems

Abstract: The Lenses Structure & Dynamics (LSD) Survey aims at studying the internal structure of luminous and dark matter - as well as their evolution - of field early-type (E/SO) galaxies to z~1. In particular, E/S0 lens galaxies are studied by combining gravitational lensing, photometric and kinematic data obtained with ground-based (VLA/Keck/VLT) and space-based telescopes (HST). Here, we report on preliminary results from the LSD Survey, in particular on (i) the constraints set on the luminous and dark-matter distributions in the inner several R_eff of E/S0 galaxies, (ii) the evolution of their stellar component and (iii) the constraints set on the value of H_0 from time-delay systems by combining lensing and kinematic data to break degeneracies in gravitational-lens models.

Measuring the Mass of High-z Galaxies with NGST

Abstract: We discuss dynamical mass measurements of high-z galaxies with the Next Generation Space Telescope (NGST). In particular, we review some of the observational limits with the current instrument/telescope generation, we discuss the redshift limits and caveats for absorption and emission lines studies with NGST, and the existence of suitable targets at high redshift. We also briefly summarize strengths and weaknesses of proposed NGST instruments for dynamical studies.