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We use a sample of 53 massive early-type strong gravitational lens galaxies with well-measured redshifts (ranging from z = 0.06 to 0.36) and stellar velocity dispersions (between 175 and 400 km s(-1)) from the Sloan Lens ACS (SLACS) Survey to derive numerous empirical scaling relations. The ratio between central stellar velocity dispersion and isothermal lens-model velocity dispersion is nearly unity within errors. The SLACS lenses define a fundamental plane (FP) that is consistent with the FP of the general population of early-type galaxies. We measure the relationship between strong-lensing mass M-lens within one-half effective radius (R-e/2) and the dimensional mass variable M-dim equivalent to G(-1) sigma(2)(e2)(R-e/2) to be log (M-lens/10(11) M-circle dot) = (1.03 +/- 0.04) log (M-dim/10(11) M-circle dot)+ (0.54 +/- 0.02) (where sigma(e2) is the projected stellar velocity dispersion within R-e/2). The near-unity slope indicates that the mass-dynamical structure of massive elliptical galaxies is independent of mass and that the "tilt'' of the SLACS FP is due entirely to variation in total (luminous plus dark) mass- to-light ratio with mass. Our results imply that dynamical masses serve as a good proxies for true masses in massive elliptical galaxies. Regarding the SLACS lenses as a homologous population, we find that the average enclosed two-dimensional (2D) mass profile goes as log[M(

We present the definitive data for the full sample of 131 strong gravitational lens candidates observed with the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope by the Sloan Lens ACS (SLACS) Survey. All targets were selected for higher redshift emission lines and lower redshift continuum in a single Sloan Digital Sky Survey (SDSS) spectrum. The foreground galaxies are primarily of early-type morphology, with redshifts from z similar or equal to 0.05 to 0.5 and velocity dispersions from sigma similar or equal to 160 to 400 km s(-1); the faint background emission-line galaxies have redshifts ranging from z similar or equal to 0.2 to 1.2. We confirm 70 systems showing clear evidence of multiple imaging of the background galaxy by the foreground galaxy, as well as an additional 19 systems with probable multiple imaging. For 63 clear lensing systems, we present singular isothermal ellipsoid and light-traces-mass gravitational lens models fitted to the ACS imaging data. These strong-lensing mass measurements are supplemented by magnitudes and effective radii measured from ACS surface brightness photometry and redshifts and velocity dispersions measured from SDSS spectroscopy. These data constitute a unique resource for the quantitative study of the interrelations between mass, light, and kinematics in massive early-type galaxies. We show that the SLACS lens sample is statistically consistent with being drawn at random from a parent sample of SDSS galaxies with comparable spectroscopic parameters and effective radii, suggesting that the results of SLACS analyses can be generalized to the massive early-type population.

We report the discovery of two concentric Einstein rings around the gravitational lens SDSS J0946+ 1006. The main lens is at redshift z(l) = 0.222, while the inner ring ( 1) is at redshift z(s1) 0.609 (R-Ein1 = 1.43 '' +/- 0.01 ''). The wider image separation ( R-Ein2 = 2.07 '' +/- 0.02 '') of the outer ring (2) implies a higher redshift than that of ring 1; the detection of ring 2 in the F814WACS filter implies an upper limit of z(s2) less than or similar to 6.9. The main lens can be described by a power- law total mass density profile rho(tot) proportional to r(-gamma ') with gamma ' = 2.00 +/- 0.03 and velocity dispersion sigma(SIE) = 287 +/- 5 km s(-1) ( the stellar velocity dispersion is sigma(v,*) = 284 +/- 24 km s(-1)). The strong lensing configuration is inconsistent with light traces mass. Adopting a prior on the stellar mass- to- light ratio from previous SLACS work, we infer a 73% +/- 9% dark matter fraction within the cylinder of radius equal to the effective radius of the lens. We find that, for the case of SDSS J0946+ 1006, the geometry of the two rings does not place interesting constraints on cosmography because of the suboptimal redshifts of lens and sources. We then consider the perturbing effect of the mass associated with ring 1 building a compound lens model. This introduces minor changes to the mass of the main lens and provides an estimate of z(s2) = 3.1(-1.0)(+2.0) and of the mass of the source responsible for ring 1 (sigma(SIE,s1) = 94(-47)(+27) km s(-1)). We conclude by examining the prospects of doing cosmography with a sample of 50 double rings, expected from future space- based surveys. Accounting for uncertainties in the mass profile of the lens and the effects of the perturber, we find that such a sample would constrain Omega(m) and within 10%, assuming flatness.

We present a weak-lensing analysis of 22 early-type (strong) lens galaxies, based on deep HST images obtained as part of the Sloan Lens ACS Survey. Using advanced techniques to control systematic uncertainties, we show that weak-lensing signal is detected out to similar to 300 h(-1) kpc (at the mean lens redshift z = 0.2). We analyze blank control fields from COSMOS in the same manner, inferring that the residual systematic uncertainty in the tangential shear is less than 0.3%. A joint strong- and weak-lensing analysis shows that the average total mass density profile is consistent with isothermal (i.e., rho proportional to r(-2)) over two decades in radius (3-300 h(-1) kpc, approximately 1-100 effective radii). This finding extends by over an order of magnitude in radius previous results, based on strong lensing and/or stellar dynamics, that luminous and dark components "conspire" to form an isothermal mass distribution. In order to disentangle the contributions of luminous and dark matter, we fit a two-component mass model (deVaucouleurs+NFW) to the weak- and strong-lensing constraints. It provides a good fit to the datawith only two free parameters: (1) the average stellar mass-to-light ratio M-*/L-V =4.48 +/- 0.46 h M-circle dot L-circle dot(-1) (at z = 0.2), in agreement with that expected for an old stellar population; (2) the average virialmass-to-light ratio M-vir/L-V = 246(-87)(+101) h M-circle dot L-circle dot(-1) Taking into account the scatter in the mass-luminosity relation, the latter result is in good agreement with semianalytical models of massive galaxy formation. The dark matter fraction inside the sphere of radius, the effective radius, is found to be 27% +/- 4%. Our results are consistent with galaxy-galaxy lensing studies of early-type galaxies that are not strong lenses, in the 30- 300 h(-1) kpc radius range. Thus, within the uncertainties, our results are representative of early- type galaxies in general.

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, breaking some classical degeneracies that have limited their individual usage, particularly in the study of high-redshift galaxies. For any given galaxy potential, the mapping of both the unknown lensed source brightness distribution and the stellar phase-space distribution function onto the photometric and kinematic observables can be cast as a single set of coupled linear equations, which are solved by maximizing the likelihood penalty function. The Bayesian evidence penalty function subsequently allows one to find the best potential-model parameters and to quantitatively rank potential-model families or other model assumptions ( e. g., PSF). 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 twointegral ( E and Lz) toroidal components, to find the maximum-likelihood two-integral distribution function in a matter of seconds in any axisymmetric potential. The nonlinear parameters of the potential are subsequently found through a hybrid MCMC and Simplex optimization of the evidence. Illustrated by the power-law potential models of Evans, we show that the inclusion of stellar kinematic constraints allows the correct linear and nonlinear model parameters to be recovered, including the potential strength, oblateness, and inclination, which, in the case of gravitational-lensing constraints only, would otherwise be fully degenerate.

We combine strong-lensing masses with SDSS stellar velocity dispersions and HST ACS effective (half-light) radii for 36 lens galaxies from the Sloan Lens ACS (SLACS) Survey to study the mass dependence of mass-dynamical structure in early-type galaxies. We find that over a 180-390 km s(-1) range in velocity dispersion, structure is independent of lensing mass to within 5%. This result suggests a systematic variation in the total (i.e., luminous plus dark matter) mass-to-light ratio as the origin of the "tilt" of the fundamental plane ( FP) scaling relationship between galaxy size, velocity dispersion, and surface brightness. We construct the FP of the lens sample, which we find to be consistent with the FP of the parent SDSS early-type galaxy population. We also present the first observational correlation between the mass-to-light ratio and residuals about the FP. Finally, we reformulate the FP in terms of surface mass density rather than surface brightness. By removing the complexities of stellar-population effects, this mass-plane formulation will facilitate comparison to numerical simulations and possible use as a cosmological distance indicator.

We present results from Planetary Nebula Spectrograph (PN. S) observations of the elliptical galaxy NGC 3379 and a description of the data reduction pipeline. We detected 214 planetary nebulae, of which 191 are ascribed to NGC 3379 and 23 to the companion galaxy NGC 3384. Comparison with data from the literature shows that the PN. S velocities have an internal error of

We present a joint gravitational lensing and stellar-dynamical analysis of 15 massive field early-type galaxies selected from the Sloan Lens ACS (SLACS) Survey. The following numerical results are found: (1) A joint likelihood gives an average logarithmic density slope for the total mass density of = 2.01(-0.03)(+0.02) (68% CL; rho(tot) proportional to r(-gamma')) = 4.2 +/- 0.4 kpc (rms of 1.6 kpc) for isotropic models. The inferred intrinsic rms spread in logarithmic density slopes is sigma(gamma') = 0.12. (2) The average position-angle difference between the light distribution and the total mass distribution is found to be = 0 degrees +/- 3 degrees (rms of 10 degrees), setting an upper limit of less than or similar to 0.035 on the average external shear. The total mass has an average ellipticity = 0.78 +/- 0.03 (rms of 0.12), which correlates extremely well with the stellar ellipticity, q(*), resulting in = 0.99 +/- 0.03 (rms of 0.11) for sigma greater than or similar to 225 km s(-1) omitting three S0 lens galaxies. (3) The average projected dark matter mass fraction is inferred to be = 0.25 +/- 0.06 (rms of 0.22) inside , using the stellar mass-to-light ratios derived from the fundamental plane as priors. (4) Combined with results from the Lenses Structure and Dynamics (LSD) Survey at z greater than or similar to 0.3, we find no significant evolution of the total density slope inside one effective radius for galaxies with sigma(ap) >= 200 km s(-1): a linear fit gives alpha(gamma') equivalent to d / dz = 0.23 +/- 0.16 (1 sigma) for the range z = 0.08-1.01. The small scatter and absence of significant evolution in the inner density slopes suggest a collisional scenario in which gas and dark matter strongly couple during galaxy formation, leading to a total mass distribution that rapidly converges to dynamical isothermality.

We use HST images to derive effective radii and effective surface brightnesses of 15 early-type (E+S0) lens galaxies identified by the SLACS Survey. Our measurements are combined with stellar velocity dispersions from the SDSS database to investigate for the first time the distribution of lens galaxies in the fundamental plane (FP) space. Accounting for selection effects (top priority to the largest Einstein radii and thus approximately to the largest velocity dispersions, σ>~240 km s-1) and for passive evolution, the distribution of the lens galaxies inside the FP is indistinguishable from that of the parent sample of SDSS galaxies. We conclude that SLACS lenses are a fair sample of high velocity dispersion E+S0s. By comparing the central stellar velocity dispersion (σ) with the velocity dispersion that best fits the lensing models (σSIE) we find ≡=1.01+/-0.02 with 0.065 rms scatter. We infer that within the Einstein radii (typically Re/2) the SLACS lenses are very well approximated by isothermal ellipsoids, requiring a fine tuning of the stellar and dark matter distribution (the bulge-halo ``conspiracy''). Interpreting the offset from the local FP in terms of evolution of the stellar mass-to-light ratio, we find dlog(M/LB)/dz=-0.69+/-0.08 (rms 0.11) consistent with the rate found for field E+S0s and with most of the stars being old (zf>2) and less than ~10% of the stellar mass having formed below z=1. We discuss our results in the context of formation mechanisms such as collisionless (``dry'') mergers. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. These observations are associated with program 10174. Support for program 10174 was provided by NASA through a grant from STScI, which is operated by the AURA, Inc., under NASA contract NAS5-26555.

The Sloan Lens ACS (SLACS) Survey is an efficient Hubble Space Telescope (HST) Snapshot imaging survey for new galaxy-scale strong gravitational lenses. The targeted lens candidates are selected spectroscopically from the Sloan Digital Sky Survey (SDSS) database of galaxy spectra for having multiple nebular emission lines at a redshift significantly higher than that of the SDSS target galaxy. The SLACS survey is optimized to detect bright early-type lens galaxies with faint lensed sources in order to increase the sample of known gravitational lenses suitable for detailed lensing, photometric, and dynamical modeling. In this paper, the first in a series on the current results of our HST Cycle 13 imaging survey, we present a catalog of 19 newly discovered gravitational lenses, along with nine other observed candidate systems that are either possible lenses, nonlenses, or nondetections. The survey efficiency is thus >= 68%. We also present Gemini 8 m and Magellan 6.5 m integral-field spectroscopic data for nine of the SLACS targets, which further support the lensing interpretation. A new method for the effective subtraction of foreground galaxy images to reveal faint background features is presented. We show that the SLACS lens galaxies have colors and ellipticities typical of the spectroscopic parent sample from which they are drawn (SDSS luminous red galaxies and quiescent MAIN sample galaxies), but are somewhat brighter and more centrally concentrated. Several explanations for the latter bias are suggested. The SLACS survey provides the first statistically significant and homogeneously selected sample of bright early-type lens galaxies, furnishing a powerful probe of the structure of early-type galaxies within the half-light radius. The high confirmation rate of lenses in the SLACS survey suggests consideration of spectroscopic lens discovery as an explicit science goal of future spectroscopic galaxy surveys.

We have determined spectroscopic ages of elliptical galaxies in the Virgo Cluster using spectra of very high signal-to-noise ratio (S/N > 100 angstrom(-1)). We observed eight galaxies with the Subaru Telescope and have combined this sample with six galaxies previously observed with the WHT. To determine their ages, we have used a new method based on the H gamma(sigma) age indicator, which is virtually independent of the effects of metallicity. Apart from ages we have estimated abundances of various elements. In this paper we present the observations, the data reduction, and the reliability of the H gamma(sigma) method. The results of this investigation are presented in a companion paper.

We present Gemini integral-field unit spectroscopy and Hubble Space Telescope (HST) F435W- and F814W-band images of a newly discovered four-image gravitational lens, SDSS J140228.22 + 632133.3 ( hereafter SDSSJ1402). The system is the first of 49 spectroscopically selected gravitational lens candidates to be imaged with the Advanced Camera for Surveys Wide-Field Channel on board HST as part of a Snapshot Survey program designed to expand the sample of known gravitational lenses amenable to detailed photometric, lensing, and dynamical studies. The lens is an r = 17.00 +/- 0.05 elliptical galaxy at a redshift of z(l) = 0.2046 +/- 0.0001, with a luminosity-weighted stellar velocity dispersion of 267 +/- 17 km s(-1) within a 3 ''-diameter aperture. Multiple emission lines place the faint lensed source galaxy at a redshift of z(s) = 0.4814 +/- 0.0001. The best-fitting singular isothermal ellipsoid lens model has an Einstein radius b = 1.'' 35 +/- 0.'' 025 (or 4.9 +/- 0.2 h(65)(-1) kpc), corresponding to an enclosed mass of (30.9 +/- 1.1) x 10(10) h(65)(-1) M-., and a rest-frame B-band mass-to-light ratio of 8.1 +/- 0.5 h(65) times solar within the same region. By calculating an expected stellar mass-to-light ratio for SDSSJ1402 using a local universe value of 7.3 +/- 2.1 h(65) and the measured evolution of the fundamental plane, we estimate the fraction of luminous matter within the Einstein radius to be 0.64 +/- 0.22: stellar mass is dominant, but some dark matter appears to be required even at this small scale of roughly one-half effective radius.

We examine the dynamics of the stars and globular clusters in the nearby giant elliptical galaxy M87 and constrain the mass distribution, using all the available data over a large range of radii, including higher order moments of the stellar line-of-sight velocity distributions and the discrete velocities of over 200 globular clusters. We introduce an extension of spherical orbit modeling methods that makes full use of all the information in the data and provides very robust constraints on the mass models. We conclusively rule out a constant mass-to-light ratio model and infer that the radial density profile of the galaxy's dark halo falls off more slowly than r(-2), suggesting that the potential of the Virgo Cluster is already dominant at r similar to 300" similar to 20 kpc.

Most elliptical galaxies contain central black holes, whose masses scale proportionally to the observed central velocity dispersions of the host galaxies according to the so-called M-BH-sigma (c) relation. Here we discuss some consequences that can be derived by combining the M-BH-sigma (c) relation with the scaling relation describing the fundamental plane of elliptical galaxies. In particular, the possibility of substantial dissipationless merging in the formation and evolution of elliptical galaxies is discussed. We enforce the merger end products to satisfy the two scaling relations mentioned above, and a major role of dissipation in galaxy formation is strongly suggested by our analysis. Moreover, we show that existing observational data may shed some light on the complex process of black hole merging.

We present a morphological study of the galaxy population of the luminous X-ray cluster MS 1054-03 at z = 0.83. The sample consists of 81 spectroscopically confirmed cluster members in a 3 x 2 h(50)(-1) Mpc area imaged in F606W and F814W with WFPC2. We find 13 ongoing mergers in MS 1054-03, comprising 17% of the L greater than or similar to L-* cluster population. Most of these mergers will likely evolve into luminous (similar to 2L(*)) elliptical galaxies, and some may evolve into SO galaxies. Assuming the galaxy population in MS 1054-03 is typical for its redshift, it is estimated that similar to 50% of present-day cluster elliptical galaxies experienced a major merger at z

We present deep Keck telescope spectroscopy of eight galaxies in the luminous X-ray cluster MS 1054-03 at z = 0.83, The data are combined with imaging observations from the Hubble Space Telescope (HST). The spectroscopic data are used to measure the internal kinematics of the galaxies, and the HST data are used to measure their structural parameters. Six galaxies have early-type spectra, and two have "E + A" spectra. The galaxies with early-type spectra define a tight fundamental plane (FP) relation. The evolution of the mass-to-light ratio is derived from the FP. The M/L ratio evolves as Delta log M/L-B proportional to -0.40z (Omega(m) = 0.3, Omega(Lambda) = 0). The observed evolution of the MIL ratio provides a combined constraint on the formation redshift of the stars, the initial mass function (IMF), and cosmological parameters. For a Salpeter IMF (x = 2.35), we find that z(form) > 2.8 and Omega(m) 0: z(form) > 1.7 if Omega(m) = 0.3 and Omega(Lambda) = 0.7. At present, the limiting factor in constraining z(form) and Omega from the observed luminosity evolution of early-type galaxies is the poor understanding of the IMF We find that if Omega(m) = 1, the IMF must be significantly steerer than the Salpeter IMF (x > 2.6).