Search

The galaxy cluster MACS J0717.5+3745 (z = 0.55) is the largest known cosmic lens, with complex internal structures seen in deep X-ray, Sunyaev-Zel'dovich effect, and dynamical observations. We perform a combined weak- and strong-lensing analysis with wide-field BVRci′z′ Subaru/Suprime-Cam observations and 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble. We find consistent weak distortion and magnification measurements of background galaxies and combine these signals to construct an optimally estimated radial mass profile of the cluster and its surrounding large-scale structure out to 5 Mpc h–1. We find consistency between strong-lensing and weak-lensing in the region where these independent data overlap, <500 kpc h–1. The two-dimensional weak-lensing map reveals a clear filamentary structure traced by distinct mass halos. We model the lensing shear field with nine halos, including the main cluster, corresponding to mass peaks detected above 2.5σκ. The total mass of the cluster as determined by the different methods is Mvir ≈ (2.8 ± 0.4) × 1015M☼. Although this is the most massive cluster known at z > 0.5, in terms of extreme value statistics, we conclude that the mass of MACS J0717.5+3745 by itself is not in serious tension with ΛCDM, representing only a ∼2σ departure above the maximum simulated halo mass at this redshift. [ABSTRACT FROM AUTHOR]

The amplitude of weak lensing should increase with source distance, rising steeply behind a lens and saturating at high redshift, providing a model-independent means of measuring cosmic geometry. We measure the amplitude of weak lensing with redshift for three massive clusters, A370 (), ZwCl0024+17 () and RXJ134711 (), using deep, three-colour Subaru imaging. We define the depth of lensed populations with reference to the COSMOS and GOODS fields, providing a consistency check of photo- z estimates over a wide range of redshift and magnitude. The predicted distance-redshift relation is followed well for the deepest data set, A370, for a wide range of cosmologies, and is consistent with less accurate data for the other two clusters. Scaling this result to a new survey of massive clusters should provide a useful cosmological constraint on , complementing existing techniques, with distance measurements covering the untested redshift range, . [ABSTRACT FROM AUTHOR]

Weak lensing work can be badly compromised by unlensed foreground and cluster members which dilute the true lensing signal. We show how the lensing amplitude in multicolour space can be harnessed to securely separate cluster members from the foreground and background populations for three massive clusters, A1703 ( z= 0.258), A370 ( z= 0.375) and RXJ1347−11 ( z= 0.451) imaged with Subaru. The luminosity functions of these clusters when corrected for dilution show similar faint-end slopes, α≃− 1.0, with no marked faint-end upturn to our limit of MR≃− 15.0, and only a mild radial gradient. In each case, the radial profile of the mass-to-light ratio ( M/ L) peaks at intermediate radius, ≃ 0.2 rvir, at a level of 300–500( M/ LR)⊙, and then falls steadily towards ∼ 100( M/ LR)⊙ at the virial radius, similar to the mean field level. This behaviour is likely due to the relative paucity of central late-type galaxies, whereas for the E/S0 sequence only a mild radial decline in M/ L is found for each cluster. We discuss this behaviour in the context of detailed simulations where predictions for tidal stripping may now be tested accurately with observations. [ABSTRACT FROM AUTHOR]

We present a joint shear-and-magnification weak-lensing analysis of a sample of 16 X-ray-regular and 4 high-magnification galaxy clusters at 0.19 ≲ z ≲ 0.69 selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). Our analysis uses wide-field multi-color imaging, taken primarily with Suprime-Cam on the Subaru Telescope. From a stacked-shear-only analysis of the X-ray-selected subsample, we detect the ensemble-averaged lensing signal with a total signal-to-noise ratio of ≃ 25 in the radial range of 200-3500 kpc h–1, providing integrated constraints on the halo profile shape and concentration-mass relation. The stacked tangential-shear signal is well described by a family of standard density profiles predicted for dark-matter-dominated halos in gravitational equilibrium, namely, the Navarro-Frenk-White (NFW), truncated variants of NFW, and Einasto models. For the NFW model, we measure a mean concentration of at an effective halo mass of . We show that this is in excellent agreement with Λ cold dark matter (ΛCDM) predictions when the CLASH X-ray selection function and projection effects are taken into account. The best-fit Einasto shape parameter is , which is consistent with the NFW-equivalent Einasto parameter of ∼0.18. We reconstruct projected mass density profiles of all CLASH clusters from a joint likelihood analysis of shear-and-magnification data and measure cluster masses at several characteristic radii assuming an NFW density profile. We also derive an ensemble-averaged total projected mass profile of the X-ray-selected subsample by stacking their individual mass profiles. The stacked total mass profile, constrained by the shear+magnification data, is shown to be consistent with our shear-based halo-model predictions, including the effects of surrounding large-scale structure as a two-halo term, establishing further consistency in the context of the ΛCDM model. [ABSTRACT FROM AUTHOR]

We derive an accurate mass distribution of the galaxy cluster MACS J1206.2-0847 (z = 0.439) from a combined weak-lensing distortion, magnification, and strong-lensing analysis of wide-field Subaru BVRcIcz′ imaging and our recent 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble program. We find good agreement in the regions of overlap between several weak- and strong-lensing mass reconstructions using a wide variety of modeling methods, ensuring consistency. The Subaru data reveal the presence of a surrounding large-scale structure with the major axis running approximately northwest-southeast (NW-SE), aligned with the cluster and its brightest galaxy shapes, showing elongation with a ∼2: 1 axis ratio in the plane of the sky. Our full-lensing mass profile exhibits a shallow profile slope dln Σ/dln R ∼ –1 at cluster outskirts (R ≳ 1 Mpc h–1), whereas the mass distribution excluding the NW-SE excess regions steepens farther out, well described by the Navarro-Frenk-White form. Assuming a spherical halo, we obtain a virial mass Mvir = (1.1 ± 0.2 ± 0.1) × 1015M☼h–1 and a halo concentration cvir = 6.9 ± 1.0 ± 1.2 (cvir ∼ 5.7 when the central 50 kpc h–1 is excluded), which falls in the range 4 ≲ 〈 c〉 ≲ 7 of average c(M, z) predictions for relaxed clusters from recent Λ cold dark matter simulations. Our full-lensing results are found to be in agreement with X-ray mass measurements where the data overlap, and when combined with Chandra gas mass measurements, they yield a cumulative gas mass fraction of 13.7+4.5– 3.0% at 0.7 Mpc h–1(≈ 1.7 r2500), a typical value observed for high-mass clusters. [ABSTRACT FROM AUTHOR]

We present a statistical weak-lensing magnification analysis on an optically selected sample of 3029 CAMIRA (Cluster finding Algorithm based on Multiband Identification of Red-sequence gAlaxies) galaxy clusters with richness N > 15 at redshift 0.2 ≤ z < 1.1 in the Subaru Hyper Suprime-Cam survey. We use two distinct populations of colour-selected, flux-limited background galaxies, namely the low- z and high- z samples at mean redshifts of ≈1.1 and ≈1.4, respectively, from which to measure the weak-lensing magnification signal by accounting for cluster contamination as well as masking effects. Our magnification bias measurements are found to be uncontaminated according to validation tests against the 'null-test' samples for which the net magnification bias is expected to vanish. The magnification bias for the full CAMIRA sample is detected at a significance level of 9.51σ, which is dominated by the high- z background. We forward-model the observed magnification data to constrain the normalization of the richness-to-mass (N – M) relation for the CAMIRA sample with informative priors on other parameters. The resulting scaling relation is N ∝ (M 500)0.92 ± 0.13(1 + z)−0.48 ± 0.69, with a characteristic richness of N = 17.72 ± 2.60 and intrinsic lognormal scatter of 0.15 ± 0.07 at M 500 = 1014  h −1 M⊙. With the derived N – M relation, we provide magnification-calibrated mass estimates of individual CAMIRA clusters, with the typical uncertainty of ≈39 and ≈32  per cent at richness of ≈20 and ≈40, respectively. We further compare our magnification-inferred N – M relation with those from the shear-based results in the literature, finding good agreement. [ABSTRACT FROM AUTHOR]

Abell 2744, a massive Hubble Frontier Fields merging galaxy cluster with many multiple images in the core has been the subject of many lens inversions using different methods. While most existing studies compare various inversion methods, we focus on a comparison of reconstructions that use different input lensing data. Since the quantity and quality of lensing data are constantly improving, it makes sense to ask if the estimated uncertainties are robust against changes in the data. We address this question using free-form grale , which takes only image information as input, and nothing pertaining to cluster galaxies. We reconstruct Abell 2744 using two sets of strong lensing data from the Hubble Frontier Fields community. Our first and second reconstructions use 55 and 91 images, respectively, and only 10 of the 91 images have the same positions and redshifts as in the first reconstruction. Comparison of the two mass maps shows that grale  uncertainties are robust against these changes, as well as small modifications in the inversion routine. Additionally, applying the methods used in Sebesta et al. for MACS J0416, we conclude that, in a statistical sense, light follows mass in Abell 2744, with brighter galaxies clustering stronger with the recovered mass than the fainter ones. We also show that the faintest galaxies are anticorrelated with mass, which is likely the result of light contamination from bright galaxies, and lensing magnification bias acting on galaxies background to the cluster. [ABSTRACT FROM AUTHOR]

Collisions and interactions between gas-rich galaxies are thought to be pivotal stages in their formation and evolution, causing the rapid production of new stars, and possibly serving as a mechanism for fueling supermassive black holes (BH). Harnessing the exquisite spatial resolution (~0.5 arcsec) afforded by the first ~170 deg2 of the Hyper Suprime-Cam (HSC) Survey, we present our new constraints on the importance of galaxy-galaxy major mergers (1:4) in growing BHs throughout the last ~8 Gyrs. Utilizing mid-infrared observations in the WISE All-Sky survey, we robustly select active galactic nuclei (AGN) and mass-matched control galaxy samples, totaling ~140,000 spectroscopically confirmed systems at i<22 mag. We identify galaxy interaction signatures using a novel machine-learning random forest decision tree technique allowing us to select statistically significant samples of major-mergers, minor-mergers/irregular-systems, and non-interacting galaxies. We use these samples to show that galaxies undergoing mergers are a factor ~2-7 more likely to contain luminous obscured AGN than non-interacting galaxies, and this is independent of both stellar mass and redshift to z < 0.9. Furthermore, based on our comparison of AGN fractions in mass-matched samples, we determine that the most luminous AGN population (LAGN > 1045 erg/s) systematically reside in merging systems over non-interacting galaxies. Our findings show that galaxy-galaxy interactions do, on average, trigger luminous AGN activity substantially more often than in secularly evolving non-interacting galaxies, and we further suggest that the BH growth rate may be closely tied to the dynamical time of the merger system. [ABSTRACT FROM AUTHOR]

We provide a new observational test for a key prediction of the ΛCDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth. We perform this test by dynamically analyzing 7 galaxy clusters, spanning the redshift range 0.13 < zc < 0.45 and caustic mass range 0.4-1.5 M☼, with an average of 293 spectroscopically confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall region, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, we identify bound galaxies. Out of these galaxies, we identify infalling and accreted halos and estimate their masses and their dynamical states. Using the estimated masses, we derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ∼0.2 and ∼0.7, we find a ∼1σ agreement with ΛCDM expectations based on the Millennium simulations I and II. At low mass ratios, ≲ 0.2, our derived contribution is underestimated since the detection efficiency decreases at low masses, ∼2 × 1014M☼. At large mass ratios, ≳ 0.7, we do not detect halos probably because our sample, which was chosen to be quite X-ray relaxed, is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated. [ABSTRACT FROM AUTHOR]

ABSTRACT Extensive surveys of galaxy clusters motivate us to assess the likelihood of cluster-cluster lensing (CCL), namely, gravitational lensing of a background cluster by a foreground cluster. We briefly describe the characteristics of CCLs in optical, X-ray and Sunyaev-Zel'dovich effect measurements, and calculate their predicted numbers for Λ cold dark matter (ΛCDM) parameters and a viable range of cluster mass functions and their uncertainties. The predicted number of CCLs in the strong-lensing regime varies from several (<10) to as high as a few dozen, depending mainly on whether lensing triaxiality bias is accounted for, through the c- M relation. A much larger number is predicted when taking into account also CCL in the weak-lensing regime. In addition to few previously suggested CCLs, we report a detection of a possible CCL in A383, where background candidate high- z structures are magnified, as seen in deep Subaru observations. [ABSTRACT FROM AUTHOR]

We outline our methods for obtaining high-precision mass profiles, combining independent weak-lensing distortion, magnification, and strong-lensing measurements. For massive clusters, the strong- and weak-lensing regimes contribute equal logarithmic coverage of the radial profile. The utility of high-quality data is limited by the cosmic noise from large-scale structure along the line of sight. This noise is overcome when stacking clusters, as too are the effects of cluster asphericity and substructure, permitting a stringent test of theoretical models. We derive a mean radial mass profile of four similar mass clusters of high-quality Hubble Space Telescope and Subaru images, in the range R = 40-2800 kpc h-1, where the inner radial boundary is sufficiently large to avoid smoothing from miscentering effects. The stacked mass profile is detected at 58σ significance over the entire radial range, with the contribution from the cosmic noise included. We show that the projected mass profile has a continuously steepening gradient out to beyond the virial radius, in remarkably good agreement with the standard Navarro-Frenk-White form predicted for the family of cold dark matter (CDM) dominated halos in gravitational equilibrium. The central slope is constrained to lie in the range, Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. The mean concentration is Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed (at Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed), which is high for relaxed, high-mass clusters, but consistent with ACDM when a sizable projection bias estimated from N-body simulations is considered. This possible tension will be more definitively explored with new cluster surveys, such as CLASH, LoCuSS, Subaru Hyper Suprime-Cam, and XXM-XXL, to construct the cvir-Mvir relation over a wider mass range. [ABSTRACT FROM AUTHOR]

The inner mass profile of the relaxed cluster Abell 1703 is analysed by two very different strong-lensing techniques applied to the deep Advanced Camera for Surveys and the Wide Field Channel 3 imaging. Our parametric method has the accuracy required to reproduce many sets of multiple images, based on the assumption that mass approximately traces light. We test this assumption with a fully non-parametric, adaptive grid method, with no knowledge of the galaxy distribution. Differences between the methods are seen on fine scales due to member galaxies which must be included in models designed to search for lensed images, but on the larger scale the general distribution of dark matter is in good agreement, with very similar radial mass profiles. We add undiluted weak-lensing measurements from deep multicolour Subaru imaging to obtain a fully model-independent mass profile out to the virial radius and beyond. Consistency is found in the region of overlap between the weak and strong lensing, and the full mass profile is well described by a Navarro, Frenk & White (NFW) model of a concentration parameter, (and ). Abell 1703 lies above the standard c- M relation predicted for the standard Λ cold dark matter model, similar to other massive relaxed clusters with accurately determined lensing-based profiles. [ABSTRACT FROM AUTHOR]

We present an improved strong-lensing analysis of Cl0024+1654 using deep Hubble Space Telescope ( HST)/Advanced Camera for Surveys (ACS)/NIC3 images, based on 33 multiply-lensed images of 11 background galaxies. These are found with a model that assumes mass approximately traces light, with a low-order expansion to allow for flexibility on large scales. The model is constrained initially by the well-known five-image system and refined as new multiply-lensed systems are identified using the model. Photometric redshifts of these new systems are then used to constrain better the mass profile by adopting the standard cosmological relation between redshift and lensing distance. Our model requires only six free parameters to describe well all positional and redshift data. The resulting inner mass profile has a slope of , consistent with new weak-lensing measurements where the data overlap, at . The combined profile is well fitted by a high-concentration Navarro, Frenk & White (NFW) mass profile, , similar to other well-studied clusters, but larger than predicted with standard Λ cold dark matter (ΛCDM). A well-defined radial critical curve is generated by the model and is clearly observed at arcsec, outlined by elongated images pointing towards the centre of mass. The relative fluxes of the multiply-lensed images are found to agree well with the modelled magnifications, providing an independent consistency check. [ABSTRACT FROM AUTHOR]

Re-ionization of the intergalactic medium occurred in the early Universe at redshift z???6-11, following the formation of the first generation of stars. Those young galaxies (where the bulk of stars formed) at a cosmic age of less than about 500 million years (z???10) remain largely unexplored because they are at or beyond the sensitivity limits of existing large telescopes. Understanding the properties of these galaxies is critical to identifying the source of the radiation that re-ionized the intergalactic medium. Gravitational lensing by galaxy clusters allows the detection of high-redshift galaxies fainter than what otherwise could be found in the deepest images of the sky. Here we report multiband observations of the cluster MACS J1149+2223 that have revealed (with high probability) a gravitationally magnified galaxy from the early Universe, at a redshift of z = 9.6?±?0.2 (that is, a cosmic age of 490?±?15 million years, or 3.6 per cent of the age of the Universe). We estimate that it formed less than 200 million years after the Big Bang (at the 95 per cent confidence level), implying a formation redshift of ?14. Given the small sky area that our observations cover, faint galaxies seem to be abundant at such a young cosmic age, suggesting that they may be the dominant source for the early re-ionization of the intergalactic medium. [ABSTRACT FROM AUTHOR]

We present multi-wavelength studies of optically defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable us to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers that is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple peaks and single clusters with single peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of merging clusters is categorized into major mergers. The average halo concentration for the merging clusters is ∼70% smaller than that of the single-peak clusters, which agrees well with predictions of numerical simulations. The spatial distribution of subhalos is less centrally concentrated than the mass distribution of the main halo. The fractions of red galaxies in the merging clusters are not higher than those of the single-peak clusters. We find a signature of the merger boost of the ICM from the stacked Planck Sunyaev–Zel'dovich effect and ROSAT X-ray luminosity, but not in optical richness. The stacked X-ray surface brightness distribution, aligned with the main subhalo pairs of low-redshift and massive clusters, shows that the central gas core is elongated along the merger axis, and overall gas distribution is misaligned by ∼60°. The homogeneous, unbiased sample of cluster mergers and multi-wavelength follow-up studies provide a unique opportunity to make a complete picture of merger physics over the whole process. [ABSTRACT FROM AUTHOR]

We precisely constrain the inner mass profile of A2261 (z = 0.225) for the first time and determine that this cluster is not “overconcentrated” as found previously, implying a formation time in agreement with ΛCDM expectations. These results are based on multiple strong-lensing analyses of new 16-band Hubble Space Telescope imaging obtained as part of the Cluster Lensing and Supernova survey with Hubble. Combining this with revised weak-lensing analyses of Subaru wide-field imaging with five-band Subaru + KPNO photometry, we place tight new constraints on the halo virial mass Mvir = (2.2 ± 0.2) × 1015M☼h–170 (within rvir ≈ 3 Mpc h–170) and concentration cvir = 6.2 ± 0.3 when assuming a spherical halo. This agrees broadly with average c(M, z) predictions from recent ΛCDM simulations, which span 5 ≲ 〈 c〉 ≲ 8. Our most significant systematic uncertainty is halo elongation along the line of sight (LOS). To estimate this, we also derive a mass profile based on archival Chandra X-ray observations and find it to be ∼35% lower than our lensing-derived profile at r2500 ∼ 600 kpc. Agreement can be achieved by a halo elongated with a ∼2:1 axis ratio along our LOS. For this elongated halo model, we find Mvir = (1.7 ± 0.2) × 1015M☼h–170 and cvir = 4.6 ± 0.2, placing rough lower limits on these values. The need for halo elongation can be partially obviated by non-thermal pressure support and, perhaps entirely, by systematic errors in the X-ray mass measurements. We estimate the effect of background structures based on MMT/Hectospec spectroscopic redshifts and find that these tend to lower Mvir further by ∼7% and increase cvir by ∼5%. [ABSTRACT FROM AUTHOR]

Hubble Space Telescope images of the galaxy cluster A2261, obtained as part of the Cluster Lensing And Supernova survey with Hubble, show that the brightest galaxy in the cluster, A2261-BCG, has the largest core yet detected in any galaxy. The cusp radius of A2261-BCG is 3.2 kpc, twice as big as the next largest core known, and ∼3 × bigger than those typically seen in the most luminous brightest cluster galaxies. The morphology of the core in A2261-BCG is also unusual, having a completely flat interior surface brightness profile, rather than the typical shallow cusp rising into the center. This implies that the galaxy has a core with constant or even centrally decreasing stellar density. Interpretation of the core as an end product of the “scouring” action of a binary supermassive black hole implies a total black hole mass ∼1010M☼ from the extrapolation of most relationships between core structure and black hole mass. The core falls 1σ above the cusp radius versus galaxy luminosity relation. Its large size in real terms, and the extremely large black hole mass required to generate it, raises the possibility that the core has been enlarged by additional processes, such as the ejection of the black holes that originally generated the core. The flat central stellar density profile is consistent with this hypothesis. The core is also displaced by 0.7 kpc from the center of the surrounding envelope, consistent with a local dynamical perturbation of the core. [ABSTRACT FROM AUTHOR]