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In recent years, breakthroughs in methods and data have enabled gravitational time delays to emerge as a very powerful tool to measure the Hubble constant H 0. However, published state-of-the-art analyses require of order 1 yr of expert investigator time and up to a million hours of computing time per system. Furthermore, as precision improves, it is crucial to identify and mitigate systematic uncertainties. With this time delay lens modelling challenge, we aim to assess the level of precision and accuracy of the modelling techniques that are currently fast enough to handle of order 50 lenses, via the blind analysis of simulated data sets. The results in Rungs 1 and 2 show that methods that use only the point source positions tend to have lower precision (⁠|$10\!-\!20{{\ \rm per\ cent}}$|⁠) while remaining accurate. In Rung 2, the methods that exploit the full information of the imaging and kinematic data sets can recover H 0 within the target accuracy (| A | < 2 per cent) and precision (<6 per cent per system), even in the presence of a poorly known point spread function and complex source morphology. A post-unblinding analysis of Rung 3 showed the numerical precision of the ray-traced cosmological simulations to be insufficient to test lens modelling methodology at the percent level, making the results difficult to interpret. A new challenge with improved simulations is needed to make further progress in the investigation of systematic uncertainties. For completeness, we present the Rung 3 results in an appendix and use them to discuss various approaches to mitigating against similar subtle data generation effects in future blind challenges. [ABSTRACT FROM AUTHOR]

The H0LiCOW collaboration inferred via strong gravitational lensing time delays a Hubble constant value of H0 = 73.3−1.8+1.7 H 0 = 73. 3 − 1.8 + 1.7 $ H_0 = 73.3^{+1.7}_{-1.8} $ km s−1 Mpc−1, describing deflector mass density profiles by either a power-law or stars (constant mass-to-light ratio) plus standard dark matter halos. The mass-sheet transform (MST) that leaves the lensing observables unchanged is considered the dominant source of residual uncertainty in H0. We quantify any potential effect of the MST with a flexible family of mass models, which directly encodes it, and they are hence maximally degenerate with H0. Our calculation is based on a new hierarchical Bayesian approach in which the MST is only constrained by stellar kinematics. The approach is validated on mock lenses, which are generated from hydrodynamic simulations. We first applied the inference to the TDCOSMO sample of seven lenses, six of which are from H0LiCOW, and measured H0 = 74.5−6.1+5.6 H 0 = 74. 5 − 6.1 + 5.6 $ H_0 = 74.5^{+5.6}_{-6.1} $ km s−1 Mpc−1. Secondly, in order to further constrain the deflector mass density profiles, we added imaging and spectroscopy for a set of 33 strong gravitational lenses from the Sloan Lens ACS (SLACS) sample. For nine of the 33 SLAC lenses, we used resolved kinematics to constrain the stellar anisotropy. From the joint hierarchical analysis of the TDCOSMO+SLACS sample, we measured H0 = 67.4−3.2+4.1 H 0 = 67. 4 − 3.2 + 4.1 $ H_0 = 67.4^{+4.1}_{-3.2} $ km s−1 Mpc−1. This measurement assumes that the TDCOSMO and SLACS galaxies are drawn from the same parent population. The blind H0LiCOW, TDCOSMO-only and TDCOSMO+SLACS analyses are in mutual statistical agreement. The TDCOSMO+SLACS analysis prefers marginally shallower mass profiles than H0LiCOW or TDCOSMO-only. Without relying on the form of the mass density profile used by H0LiCOW, we achieve a ∼5% measurement of H0. While our new hierarchical analysis does not statistically invalidate the mass profile assumptions by H0LiCOW – and thus the H0 measurement relying on them – it demonstrates the importance of understanding the mass density profile of elliptical galaxies. The uncertainties on H0 derived in this paper can be reduced by physical or observational priors on the form of the mass profile, or by additional data. [ABSTRACT FROM AUTHOR]

We present an analysis of seven strongly gravitationally lensed quasars and the corresponding constraints on the properties of dark matter. Our results are derived by modelling the lensed image positions and flux-ratios using a combination of smooth macro-models and a population of low-mass haloes within the mass range of 106–109 M⊙. Our lens models explicitly include higher order complexity in the form of stellar discs and luminous satellites, as well as low-mass haloes located along the observed lines of sight for the first time. Assuming a cold dark matter (CDM) cosmology, we infer an average total mass fraction in substructure of |$f_{\rm sub} = 0.012^{+0.007}_{-0.004}$| (68 per cent confidence limits), which is in agreement with the predictions from CDM hydrodynamical simulations to within 1σ. This result is closer to the predictions than those from previous studies that did not include line-of-sight haloes. Under the assumption of a thermal relic dark matter model, we derive a lower limit on the particle relic mass of m th > 5.58 keV (95 per cent confidence limits), which is consistent with a value of m th > 5.3 keV from the recent analysis of the Ly α forest. We also identify two main sources of possible systematic errors and conclude that deeper investigations in the complex structure of lens galaxies as well as the size of the background sources should be a priority for this field. [ABSTRACT FROM AUTHOR]

Galaxies and galaxy groups located along the line of sight towards gravitationally lensed quasars produce high-order perturbations of the gravitational potential at the lens position. When these perturbation are too large, they can induce a systematic error on H 0 of a few per cent if the lens system is used for cosmological inference and the perturbers are not explicitly accounted for in the lens model. In this work, we present a detailed characterization of the environment of the lens system WFI 2033−4723 (⁠|$z_{\rm src} =\,$| 1.662, |$z_{\rm lens}=\,$| 0.6575), one of the core targets of the H0LiCOW project for which we present cosmological inferences in a companion paper. We use the Gemini and ESO-Very Large telescopes to measure the spectroscopic redshifts of the brightest galaxies towards the lens, and use the ESO-MUSE integral field spectrograph to measure the velocity-dispersion of the lens (⁠|$\sigma _{\rm {los}}= 250^{+15}_{-21}$|  km s−1) and of several nearby galaxies. In addition, we measure photometric redshifts and stellar masses of all galaxies down to i < 23 mag, mainly based on Dark Energy Survey imaging (DR1). Our new catalogue, complemented with literature data, more than doubles the number of known galaxy spectroscopic redshifts in the direct vicinity of the lens, expanding to 116 (64) the number of spectroscopic redshifts for galaxies separated by less than 3 arcmin (2 arcmin ) from the lens. Using the flexion-shift as a measure of the amplitude of the gravitational perturbation, we identify two galaxy groups and three galaxies that require specific attention in the lens models. The ESO MUSE data enable us to measure the velocity-dispersions of three of these galaxies. These results are essential for the cosmological inference analysis presented in Rusu et al. [ABSTRACT FROM AUTHOR]

We use a sample of 17 strong gravitational lens systems from the BELLS GALLERY survey to quantify the amount of low-mass dark matter haloes within the lensing galaxies and along their lines of sight, and to constrain the properties of dark matter. Based on a detection criterion of 10σ, we report no significant detection in any of the lenses. Using the sensitivity function at the 10σ level, we have calculated the predicted number of detectable cold dark matter (CDM) line-of-sight haloes to be μ l  = 1.17 ± 1.08, in agreement with our null detection. Assuming a detection sensitivity that improved to the level implied by a 5σ threshold, the expected number of detectable line-of-sight haloes rises to μ l  = 9.0 ± 3.0. Whilst the current data find zero detections at this sensitivity level (which has a probability of P |$^{{\rm 5}\sigma }_{{\rm CDM}}(n_{\rm det}=0)$|  = 0.0001 and would be in strong tension with the CDM framework), we find that such a low-detection threshold leads to many spurious detections and non-detections and therefore the current lack of detections is unreliable and requires data with improved sensitivity. Combining this sample with a subsample of 11 SLACS lenses, we constrain the half-mode mass to be log (M hm) < 12.26 at the 2σ level. The latter is consistent with resonantly produced sterile neutrino masses m s < 0.8 keV at any value of the lepton asymmetry at the 2σ level. [ABSTRACT FROM AUTHOR]

We present a study of 17 LAEs at redshift 2 < z < 3 gravitationally lensed by massive early-type galaxies (ETGs) at a mean redshift of approximately 0.5. Using a fully Bayesian grid-based technique, we model the gravitational lens mass distributions with elliptical power-law profiles and reconstruct the ultraviolet (UV)-continuum surface-brightness distributions of the background sources using pixellated source models. We find that the deflectors are close to, but not consistent with isothermal models in almost all cases, at the 2σ level. We take advantage of the lensing magnification (typically |$\mu$| ≃ 20) to characterize the physical and morphological properties of these LAE galaxies. From reconstructing the ultraviolet continuum emission, we find that the star formation rates range from 0.3 to 8.5 M⊙ yr−1 and that the galaxies are typically composed of several compact and diffuse components, separated by 0.4–4 kpc. Moreover, they have peak star formation rate intensities that range from 2.1 to 54.1 M⊙ yr−1 kpc−2. These galaxies tend to be extended with major axis ranging from 0.2 to 1.8 kpc (median 561 pc), and with a median ellipticity of 0.49. This morphology is consistent with disc-like structures of star formation for more than half of the sample. However, for at least two sources, we also find off-axis components that may be associated with mergers. Resolved kinematical information will be needed to confirm the disc-like nature and possible merger scenario for the LAEs in the sample. [ABSTRACT FROM AUTHOR]

We report the discovery of a new gravitationally lensed quasar (double) from the Optical Gravitational Lensing Experiment (OGLE) identified inside the ~670deg2 area encompassing the Magellanic Clouds. The source was selected as one of ~60 'red W1 - W2' mid-infrared objects from WISE and having a significant amount of variability in OGLE for both two (or more) nearby sources. This is the first detection of a gravitational lens, where the discovery is made 'the other way around', meaning we first measured the time delay between the two lensed quasar images of -132 < tAB < -76 d (90 per cent CL), with the median tAB ≈-102 d (in the observer frame), and where the fainter image B lags image A. The system consists of the two quasar images separated by 1.5 arcsec on the sky, with I ≈20.0mag and I ≈19.6mag, respectively, and a lensing galaxy that becomes detectable as I ≈21.5 mag source, 1.0 arcsec from image A, after subtracting the two lensed images. Both quasar images show clear AGN broad emission lines at z=2.16 in the New Technology Telescope spectra. The spectral energy distribution (SED) fitting with the fixed source redshift provided the estimate of the lensing galaxy redshift of z ≈0.9 ± 0.2 (90 per cent CL), while its type is more likely to be elliptical (the SED-inferred and lens-model stellar mass is more likely present in ellipticals) than spiral (preferred redshift by the lens model). [ABSTRACT FROM AUTHOR]

Galaxies located in the environment or along the line of sight towards gravitational lenses can significantly affect lensing observables, and can lead to systematic errors on the measurement of H0 from the time-delay technique. We present the results of a systematic spectroscopic identification of the galaxies in the field of view of the lensed quasar HE 0435-1223 using the W. M. Keck, Gemini and ESO-Very Large telescopes. Our new catalogue triples the number of known galaxy redshifts in the direct vicinity of the lens, expanding to 102 the number of measured redshifts for galaxies separated by less than 3 arcmin from the lens.We complement our catalogue with literature data to gather redshifts up to 15 arcmin from the lens, and search for galaxy groups or clusters projected towards HE 0435-1223. We confirm that the lens is a member of a small group that includes at least 12 galaxies, and find 8 other group candidates near the line of sight of the lens. The flexion shift, namely the shift of lensed images produced by high-order perturbation of the lens potential, is calculated for each galaxy/group and used to identify which objects produce the largest perturbation of the lens potential. This analysis demonstrates that (i) at most three of the five brightest galaxies projected within 12 arcsec of the lens need to be explicitly used in the lens models, and (ii) the groups can be treated in the lens model as an external tidal field (shear) contribution. [ABSTRACT FROM AUTHOR]

Strong gravitational lens systems with time delays between the multiple images allow measurements of time-delay distances, which are primarily sensitive to the Hubble constant that is key to probing dark energy, neutrino physics and the spatial curvature of the Universe, as well as discovering new physics. We present H0LiCOW (H0 Lenses in COSMOGRAIL's Wellspring), a program that aims to measure H0 with <3.5 per cent uncertainty from five lens systems (B1608+656, RXJ1131-1231, HE 0435-1223, WFI2033-4723 and HE 1104-1805). We have been acquiring (1) time delays through COSMOGRAIL and Very Large Array monitoring, (2) high-resolution Hubble Space Telescope imaging for the lens mass modelling, (3) wide-field imaging and spectroscopy to characterize the lens environment and (4) moderate-resolution spectroscopy to obtain the stellar velocity dispersion of the lenses for mass modelling. In cosmological models with one-parameter extension to flat Λ cold dark matter, we expect to measure H0 to <3.5 per cent in most models, spatial curvature Ωk to 0.004, w to 0.14 and the effective number of neutrino species to 0.2 (1σ uncertainties) when combined with current cosmic microwave background (CMB) experiments. These are, respectively, a factor of ~15, ~2 and ~1.5 tighter than CMB alone. Our data set will further enable us to study the stellar initial mass function of the lens galaxies, and the co-evolution of supermassive black holes and their host galaxies. This program will provide a foundation for extracting cosmological distances from the hundreds of time-delay lenses that are expected to be discovered in current and future surveys. [ABSTRACT FROM AUTHOR]

We present a new measurement of the Hubble Constant H0 and other cosmological parameters based on the joint analysis of three multiply imaged quasar systems with measured gravitational time delays. First, we measure the time delay of HE 0435-1223 from 13-yr light curves obtained as part of the COSMOGRAIL project. Companion papers detail the modelling of the main deflectors and line-of-sight effects, and how these data are combined to determine the time-delay distance of HE 0435-1223. Crucially, the measurements are carried out blindly with respect to cosmological parameters in order to avoid confirmation bias. We then combine the time-delay distance of HE 0435-1223 with previous measurements from systems B1608+656 and RXJ1131-1231 to create a Time Delay Strong Lensing probe (TDSL). In flat Λ cold dark matter (ΛCDM) with free matter and energy density, we find H0 =71.9-3.0+2.4 kms-1Mpc-1 and ΩΛ=0.62-0.35+0.24 . This measurement is completely independent of, and in agreement with, the local distance ladder measurements of H0. We explore more general cosmological models combining TDSL with other probes, illustrating its power to break degeneracies inherent to other methods. The joint constraints from TDSL and Planck are H0 = 69.2-2.2+1.4 kms-1Mpc-1, ΩΛ=0.70-0.01+0.01 and Ωk=0.003-0.006+0.004 in open ΛCDM and H0 =79.0-4.2+4.4 kms-1Mpc-1, Ωde=0.77-0.03+0.02 and w=-1.38-0.16+0.14 in flat wCDM. In combination with Planck and baryon acoustic oscillation data, when relaxing the constraints on the numbers of relativistic species we find Neff = 3.34-0.21+0.21 in NeffΛCDM and when relaxing the total mass of neutrinos we find Σmv ≤ 0.182 eV in mvΛCDM. Finally, in an open wCDM in combination with Planck and cosmic microwave background lensing, we find H0 =77.9-4.2+5.0 kms-1 Mpc-1, Ωde=0.77-0.03+0.03, Ωk=-0.003-0.004+0.004 and w=-1.37-0.23+0.18. [ABSTRACT FROM AUTHOR]

We present spectroscopic confirmation of two new gravitationally lensed quasars, discovered in the Dark Energy Survey (DES) and Wide-field Infrared Survey Explorer (WISE) based on their multiband photometry and extended morphology in DES images. Images of DES J0115-5244 show a red galaxy with two blue point sources at either side, which are images of the same quasar at zs = 1.64 as obtained by our long-slit spectroscopic data. The Einstein radius estimated from the DES images is 0.51 arcsec. DES J2146-0047 is in the area of overlap between DES and the Sloan Digital Sky Survey (SDSS). Two blue components are visible in the DES and SDSS images. The SDSS fibre spectrum shows a quasar component at zs = 2.38 and absorption by Mg II and Fe II at zl = 0.799, which we tentatively associate with the foreground lens galaxy. Our long-slit spectra show that the blue components are resolved images of the same quasar. The Einstein radius is 0.68 arcsec, corresponding to an enclosed mass of 1.6 × 1011M๏. Three other candidates were observed and rejected, two being low-redshift pairs of starburst galaxies, and one being a quasar behind a blue star. These first confirmation results provide an important empirical validation of the data mining and model-based selection that is being applied to the entire DES data set. [ABSTRACT FROM AUTHOR]

Strong gravitational lenses can be used to detect low-mass subhaloes, based on deviations in image fluxes and positions from what can be achieved with a smooth mass distribution. So far, this method has been limited by the small number of (radio-loud, microlensing-free) systems which can be analysed for the presence of substructure. Using the gravitational lens B1422+231, we demonstrate that adaptive optics integral field spectroscopy can also be used to detect dark substructures. We analyse data obtained with OH Suppressing Infra-Red Imaging Spectrograph on the Keck i Telescope, using a Bayesian method that accounts for uncertainties relating to the point spread function and image positions in the separate exposures. The narrow-line [O iii] fluxes measured for the lensed images are consistent with those measured in the radio, and show a significant deviation from what would be expected in a smooth mass distribution, consistent with the presence of a perturbing low-mass halo. Detailed lens modelling shows that image fluxes and positions are fitted significantly better when the lens is modelled as a system containing a single perturbing subhalo in addition to the main halo, rather than by the main halo on its own, indicating the significant detection of substructure. The inferred mass of the subhalo depends on the subhalo mass density profile: the 68 per cent confidence intervals for the perturber mass within 600 pc are 8.2$^{+0.6}_{-0.8}$, 8.2$^{+0.6}_{-1}$ and 7.6 ± 0.3 log10[Msub/M⊙], respectively, for a singular isothermal sphere, a pseudo-Jaffe and a Navarro–Frenk–White mass profile. This method can extend the study of flux ratio anomalies to virtually all quadruply imaged quasars, and therefore offers great potential to improve the determination of the subhalo mass function in the near future. [ABSTRACT FROM AUTHOR]

We present the results of a search for galaxy substructures in a sample of 11 gravitational lens galaxies from the Sloan Lens ACS Survey by Bolton et al. We find no significant detection of mass clumps, except for a luminous satellite in the system SDSS J0956+5110. We use these non-detections, in combination with a previous detection in the system SDSS J0946+1006, to derive constraints on the substructure mass function in massive early-type host galaxies with an average redshift 〈zlens〉 ∼ 0.2 and an average velocity dispersion 〈σeff〉 ∼ 270 km s−1. We perform a Bayesian inference on the substructure mass function, within a median region of about 32 kpc2 around the Einstein radius (〈Rein〉 ∼ 4.2 kpc). We infer a mean projected substructure mass fraction f = $0.0076_{-0.0052}^{+0.0208}$ at the 68 per cent confidence level and a substructure mass function slope α < 2.93 at the 95 per cent confidence level for a uniform prior probability density on α. For a Gaussian prior based on cold dark matter (CDM) simulations, we infer f = $0.0064^{+0.0080}_{-0.0042}$ and a slope of α = $1.90^{+0.098}_{-0.098}$ at the 68 per cent confidence level. Since only one substructure was detected in the full sample, we have little information on the mass function slope, which is therefore poorly constrained (i.e. the Bayes factor shows no positive preference for any of the two models). The inferred fraction is consistent with the expectations from CDM simulations and with inference from flux ratio anomalies at the 68 per cent confidence level. [ABSTRACT FROM AUTHOR]

Strong gravitational lenses with measured time delays between the multiple images and models of the lens mass distribution allow a one-step determination of the time-delay distance, and thus a measure of cosmological parameters. We present a blind analysis of the gravitational lens RXJ1131-1231 incorporating (1) the newly measured time delays from COSMOGRAIL, the COSmological MOnitoring of GRAvItational Lenses, (2) archival Hubble Space Telescope imaging of the lens system, (3) a new velocity-dispersion measurement of the lens galaxy of 323 ± 20 km s-1 based on Keck spectroscopy, and (4) a characterization of the line-of-sight structures via observations of the lens' environment and ray tracing through the Millennium Simulation. Our blind analysis is designed to prevent experimenter bias. The joint analysis of the data sets allows a time-delay distance measurement to 6% precision that takes into account all known systematic uncertainties. In combination with the Wilkinson Microwave Anisotropy Probe seven-year (WMAP7) data set in flat wCDM cosmology, our unblinded cosmological constraints for RXJ1131-1231 are H0 = 80.0+5.8-5.7 km s-1 Mpc-1, Ωde = 0.79 ± 0.03, and w = -1.25+0.17 -0.21. We find the results to be statistically consistent with those from the analysis of the gravitational lens B1608+656, permitting us to combine the inferences from these two lenses. The joint constraints from the two lenses and WMAP7 are H0 = 75.2+4.4 -4.2 km s-1 Mpc-1, Ωde = 0.76+0.02 -0.03, and w = -1.14+0.17 -0.20 in flat wCDM, and H0 = 73.1+2.4 -3.6 km s-1 Mpc-1, Ω⋀ = 0.75+0.01 -0.02, and Ωk = 0.003+0.005 -0.006 in open ⋀CDM. Time-delay lenses constrain especially tightly the Hubble constant H0 (5.7% and 4.0% respectively in wCDM and open ⋀CDM) and curvature of the universe. The overall information content is similar to that of Baryon Acoustic Oscillation experiments. Thus, they complement well other cosmological probes, and provide an independent check of unknown systematics. Our measurement of the Hubble constant is completely independent of those based on the local distance ladder method, providing an important consistency check of the standard cosmological model and of general relativity. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the possibility of constraining the dark energy equation of state by measuring the ratio of Einstein radii in a strong gravitational lens system with two source planes. This quantity is independent of the Hubble parameter and directly measures the growth of angular diameter distances as a function of redshift. We investigate the prospects for a single double-source plane system and for a forecast population of systems discovered by re-observing a population of single-source lenses already known from a photometrically selected catalogue such as Cambridge and Sloan survey of wide arcs in the sky or from a spectroscopically selected catalogue such as Sloan Lens ACS survey. We find that constraints comparable to current data sets (σ( w) ∼ 15 per cent) are possible with a handful of double-source plane systems. We also find that the method's degeneracy between ΩM and w is almost orthogonal to that of cosmic microwave background and Baryon Acoustic Oscillations measurements, making this method highly complimentary to current probes. [ABSTRACT FROM AUTHOR]

ABSTRACT We present new mass models for the gravitational lens system B1938+666, using multiwavelength data acquired from Keck adaptive optics (AO) and Hubble Space Telescope ( HST) observations. These models are the first results from the Strong lensing at High Angular Resolution Program (SHARP), a project designed to study known quadruple image and Einstein ring lenses using high-resolution imaging, in order to probe their mass distributions in unprecedented detail. Here, we specifically highlight differences between AO- and HST-derived lens models, finding that - at least when the lens and source galaxies are both bright and red, and the system has a high degree of circular symmetry - AO-derived models place significantly tighter constraints on model parameters. Using this improved precision, we infer important physical properties about the B1938+666 system, including the mass density slope of the lensing galaxy (γ = 2.045), the projected dark matter mass fraction within the Einstein radius ( Mdark/ Mlens = 0.55) and the total magnification factor of the source galaxy (∼13). Additionally, we measure an upper-limit constraint on luminous substructure ( MV > 16.2), based on the non-detection of bright satellite galaxies in all data sets. Finally, we utilize the improved image resolution of the AO data to reveal the presence of faint arcs outside of the primary Einstein ring. The positions and orientations of these arcs raise the intriguing possibility that B1938+666 has a second source galaxy, located at a more distant redshift. However, future work is needed to verify this hypothesis. [ABSTRACT FROM AUTHOR]

Measuring the relative mass contributions of luminous and dark matter in spiral galaxies is important for understanding their formation and evolution. The combination of a galaxy rotation curve and strong lensing is a powerful way to break the disk--halo degeneracy that is inherent in each of the methods individually. We present an analysis of the 10 image radio spiral lens B1933+503 at z1 = 0.755, incorporating (1) new global very long baseline interferometry observations, (2) new adaptive-optics-assisted K-band imaging, and (3) new spectroscopic observations for the lens galaxy rotation curve and the source redshift. We construct a three-dimensionally axisymmetric mass distribution with three components: an exponential profile for the disk, a point mass for the bulge, and a Navarro--Frenk--White (NFW) profile for the halo. The mass model is simultaneously fitted to the kinematics and the lensing data. The NFW halo needs to be oblate with a flattening of a/c = 0.33-0.05+0.07 to be consistent with the radio data. This suggests that baryons are effective at making the halos oblate near the center. The lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we obtain a lower limit on the halo scale radius of 16 kpc (95% credible intervals). The dark matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is fDM,2.2 = 0.43-0.09+0.10. The contribution of the disk to the total circular velocity at 2.2 disk +0.05 scale lengths is 0.76-0.06+0.05, suggesting that the disk is marginally submaximal. The stellar mass of the disk from our modeling is log10 (M* /M☉) = 11.06-0.11+0.09 assuming that the cold gas contributes ~20% to the total disk mass. In comparison to the stellar masses estimated from stellar population synthesis models, the stellar initial mass function of Chabrier is preferred to that of Salpeter by a probability factor of 7.2. [ABSTRACT FROM AUTHOR]

We use Keck laser guide star adaptive optics imaging and exploit the magnifying effects of strong gravitational lensing (the effective resolution is FWHM ≈ 200 pc) to investigate the sub-kpc scale of an intermediate-redshift (), massive early-type galaxy being lensed by a foreground early-type galaxy; we dub this class of strong gravitational lens systems EELs, i.e. early-type/early-type lenses. We find that the background source is massive ( M) and compact (), and a two-component fit is required to model accurately the surface brightness distribution, including an extended low-surface-brightness component. This extended component may arise from the evolution of higher redshift 'red nuggets' or may already be in place at but is unobservable due to cosmological surface brightness dimming. [ABSTRACT FROM AUTHOR]

The gravitational lens system CLASS B2108+213 has two radio-loud lensed images separated by 4.56 arcsec. The relatively large image separation implies that the lensing is caused by a group of galaxies. In this paper, new optical imaging and spectroscopic data for the lensing galaxies of B2108+213 and the surrounding field galaxies are presented. These data are used to investigate the mass and composition of the lensing structure. The redshift and stellar velocity dispersion of the main lensing galaxy (G1) are found to be and km s−1, respectively. The optical spectrum of the lensed quasar shows no obvious emission or absorption features, and is consistent with a BL Lac type radio source. However, the tentative detection of the G-band and Mg-b absorption lines, and a break in the spectrum of the host galaxy of the lensed quasar gives a likely source redshift of . Spectroscopy of the field around B2108+213 finds 51 galaxies at a similar redshift to G1, thus confirming that there is a much larger structure at associated with this system. The width of the group velocity distribution is 694 ± 93 km s−1, but is non-Gaussian, implying that the structure is not yet viralized. The main lensing galaxy is also the brightest group member and has a surface brightness profile consistent with a typical cD galaxy. A lensing and dynamics analysis of the mass distribution, which also includes the newly found group members, finds that the logarithmic slope of the mass density profile is on average isothermal inside the Einstein radius, but steeper at the location of the Einstein radius. This apparent change in slope can be accounted for if an external convergence gradient, representing the underlying parent halo of the galaxy group, is included in the mass model. [ABSTRACT FROM AUTHOR]

The mass function of dwarf satellite galaxies that are observed around Local Group galaxies differs substantially from simulations based on cold dark matter: the simulations predict many more dwarf galaxies than are seen. The Local Group, however, may be anomalous in this regard. A massive dark satellite in an early-type lens galaxy at a redshift of 0.222 was recently found using a method based on gravitational lensing, suggesting that the mass fraction contained in substructure could be higher than is predicted from simulations. The lack of very low-mass detections, however, prohibited any constraint on their mass function. Here we report the presence of a (1.9?±?0.1)?×?108 dark satellite galaxy in the Einstein ring system JVAS B1938+666 (ref. 11) at a redshift of 0.881, where denotes the solar mass. This satellite galaxy has a mass similar to that of the Sagittarius galaxy, which is a satellite of the Milky Way. We determine the logarithmic slope of the mass function for substructure beyond the local Universe to be , with an average mass fraction of per cent, by combining data on both of these recently discovered galaxies. Our results are consistent with the predictions from cold dark matter simulations at the 95 per cent confidence level, and therefore agree with the view that galaxies formed hierarchically in a Universe composed of cold dark matter. [ABSTRACT FROM AUTHOR]

We infer the normalization and the radial and angular distributions of the number density of satellites of massive galaxies (log10[M*h/M☼] > 10.5) between redshifts 0.1 and 0.8 as a function of host stellar mass, redshift, morphology, and satellite luminosity. Exploiting the depth and resolution of the COSMOS Hubble Space Telescope images, we detect satellites up to 8 mag fainter than the host galaxies and as close as 0.3 (1.4) arcsec (kpc). Describing the number density profile of satellite galaxies to be a projected power law such that , we find γp = –1.1 ± 0.3. We find no dependency of γp on host stellar mass, redshift, morphology, or satellite luminosity. Satellites of early-type hosts have angular distributions that are more flattened than the host light profile and are aligned with its major axis. No significant average alignment is detected for satellites of late-type hosts. The number of satellites within a fixed magnitude contrast from a host galaxy is dependent on its stellar mass, with more massive galaxies hosting significantly more satellites. Furthermore, high-mass late-type hosts have significantly fewer satellites than early-type galaxies of the same stellar mass, possibly indicating that they reside in more massive halos. No significant evolution in the number of satellites per host is detected. The cumulative luminosity function of satellites is qualitatively in good agreement with that predicted using SubHalo Abundance Matching techniques. However, there are significant residual discrepancies in the absolute normalization, suggesting that properties other than the host galaxy luminosity or stellar mass determine the number of satellites. [ABSTRACT FROM AUTHOR]

Stars and dark matter account for most of the mass of early-type galaxies, but uncertainties in the stellar population and the dark matter profile make it challenging to distinguish between the two components. Nevertheless, precise observations of stellar and dark matter are extremely valuable for testing the many models of structure formation and evolution. We present a measurement of the stellar mass and inner slope of the dark matter halo of a massive early-type galaxy at z = 0.222. The galaxy is the foreground deflector of the double Einstein ring gravitational lens system SDSSJ0946+1006, also known as the “Jackpot.” By combining the tools of lensing and dynamics we first constrain the mean slope of the total mass density profile () within the radius of the outer ring to be γ′ = 1.98 ± 0.02 ± 0.01. Then we obtain a bulge-halo decomposition, assuming a power-law form for the dark matter halo. Our analysis yields γDM = 1.7 ± 0.2 for the inner slope of the dark matter profile, in agreement with theoretical findings on the distribution of dark matter in ellipticals, and a stellar mass from lensing and dynamics MLD* = 5.5–1.3+0.4 × 1011M☼. By comparing this measurement with stellar masses inferred from stellar population synthesis fitting we find that a Salpeter initial mass function (IMF) provides a good description of the stellar population of the lens while the probability of the IMF being heavier than Chabrier is 95%. Our data suggest that growth by accretion of small systems from a compact red nugget is a plausible formation scenario for this object. [ABSTRACT FROM AUTHOR]

We report on an investigation of the environments of the Sloan Lens ACS Survey (SLACS) sample of gravitational lenses. The local and global environments of the lenses are characterized using Sloan Digital Sky Survey (SDSS) photometry and, when available, spectroscopy. We find that the lens systems that are best modelled with steeper than isothermal density profiles are more likely to have close companions than lenses with shallower than isothermal profiles. This suggests that the profile steepening may be caused by interactions with a companion galaxy as indicated by N-body simulations of group galaxies. The global environments of the SLACS lenses are typical of non-lensing SDSS galaxies with comparable properties to the lenses, and the richnesses of the lens groups are not as strongly correlated with the lens density profiles as are the local environments. Furthermore, we investigate the possibility of line-of-sight contamination affecting the lens models, but do not find a significant over-density of sources compared to lines of sight without lenses. [ABSTRACT FROM AUTHOR]