Search

We report the discovery of four galaxy candidates observed 450–600 Myr after the Big Bang with photometric redshifts between z ∼ 8.3 and 10.2 measured using James Webb Space Telescope (JWST) NIRCam imaging of the galaxy cluster WHL0137−08 observed in eight filters spanning 0.8–5.0 μ m, plus nine Hubble Space Telescope filters spanning 0.4–1.7 μ m. One candidate is gravitationally lensed with a magnification of μ ∼ 8, while the other three are located in a nearby NIRCam module with expected magnifications of μ ≲ 1.1. Using SED fitting, we estimate the stellar masses of these galaxies are typically in the range log M ⋆ / M ⊙ = 8.3–8.7. All appear young, with mass-weighted ages <240 Myr, low dust content A V < 0.15 mag, and specific star formation rates sSFR ∼0.25–10 Gyr−1 for most. One z ∼ 9 candidate is consistent with an age <5 Myr and an sSFR ∼10 Gyr−1, as inferred from a strong F444W excess, implying [O iii ]+H β rest-frame equivalent width ∼2000 Å, although an older z ∼ 10 object is also allowed. Another z ∼ 9 candidate is lensed into an arc 2.″4 long with a magnification of μ ∼ 8. This arc is the most spatially resolved galaxy at z ∼ 9 known to date, revealing structures ∼30 pc across. Follow-up spectroscopy of WHL0137−08 with JWST/NIRSpec will be useful to spectroscopically confirm these high-redshift galaxy candidates and to study their physical properties in more detail. [ABSTRACT FROM AUTHOR]

We report the discovery of a transient seen in a strongly lensed arc at redshift z s = 1.2567 in Hubble Space Telescope imaging of the Abell 370 galaxy cluster. The transient is detected at 29.51 ± 0.14 AB mag in a WFC3/UVIS F200LP difference image made using observations from two different epochs, obtained in the framework of the Flashlights programme, and is also visible in the F350LP band (m F350LP ≈ 30.53 ± 0.76 AB mag). The transient is observed on the negative-parity side of the critical curve at a distance of ∼0.6 arcsec from it, greater than previous examples of lensed stars. The large distance from the critical curve yields a significantly smaller macromagnification, but our simulations show that bright, O/B-type supergiants can reach sufficiently high magnifications to be seen at the observed position and magnitude. In addition, the observed transient image is a trailing image with an observer-frame time delay of ∼+0.8 d from its expected counterpart, so that any transient lasting for longer than that should have also been seen on the minima side and is thus excluded. This, together with the blue colour we measure for the transient (m F200LP − m F350LP ≈ [−0.3, −1.6] AB), rules out most other transient candidates such as (kilo)novae, for example, and makes a lensed star the prime candidate. Assuming that the transient is indeed a lensed star as suggested, many more such events should be detected in the near future in cluster surveys with the Hubble Space Telescope and JWST. [ABSTRACT FROM AUTHOR]

We present a first strong-lensing model for the galaxy cluster RM J121218.5+273255.1 (z = 0.35; hereafter RMJ1212; also known as A1489). This cluster is among the top 0.1% richest clusters in the redMaPPer catalog; it is significantly detected in X-ray and through the Sunyaev–Zel'dovich effect in ROSAT and Planck data, respectively, and its optical luminosity distribution implies a very large lens, following mass-to-light scaling relations. Based on these properties it was chosen for the Webb Medium Deep Fields (WMDF) James Webb Space Telescope/Guaranteed Time Observations program. In preparation for this program, RMJ1212 was recently imaged with Gemini Multi-Object Spectrograph (GMOS) on Gemini North and in seven optical and near-infrared bands with the Hubble Space Telescope (HST). We use these data to map the inner mass distribution of the cluster, uncovering various sets of multiple images. We also search for high-redshift candidates in the data, as well as for transient sources. We find over a dozen high-redshift (z ≳ 6) candidates based on both photometric redshift and the dropout technique. No prominent (≳5σ) transients were found in the data between the two HST visits. Our lensing analysis reveals a relatively large lens with an effective Einstein radius of θE ≃ 32 ± 3″ (zs = 2), in broad agreement with the scaling-relation expectations. RMJ1212 demonstrates that powerful lensing clusters can be selected in a robust and automated way following the light-traces-mass assumption. [ABSTRACT FROM AUTHOR]

The nondetection of dark matter (DM) particles in increasingly stringent laboratory searches has encouraged alternative gravity theories where gravity is sourced only from visible matter. Here, we consider whether such theories can pass a two-dimensional test posed by gravitational lensing—to reproduce a particularly detailed Einstein ring in the core of the galaxy cluster A3827. We find that when we require the lensing mass distribution to strictly follow the shape (ellipticity and position angle) of the light distribution of cluster member galaxies, intracluster stars, and the X-ray emitting intracluster medium, we cannot reproduce the Einstein ring, despite allowing the mass-to-light ratios of these visible components to freely vary with radius to mimic alternative gravity theories. Alternatively, we show that the detailed features of the Einstein ring are accurately reproduced by allowing a smooth, freely oriented DM halo in the lens model, with relatively small contributions from the visible components at a level consistent with their observed brightnesses. This dominant DM component is constrained to have the same orientation as the light from the intracluster stars, indicating that the intracluster stars trace the gravitational potential of this component. The Einstein ring of A3827 therefore presents a new challenge for alternative gravity theories: not only must such theories find agreement between the total lensing mass and visible mass, but they must also find agreement between the projected sky distribution of the lensing mass and that of the visible matter, a more stringent test than has hitherto been posed by lensing data. [ABSTRACT FROM AUTHOR]

Using Planck satellite data, we construct Sunyaev–Zel'dovich (SZ) gas pressure profiles for a large, volume-complete sample of optically selected clusters. We have defined a sample of over 8000 redMaPPer clusters from the Sloan Digital Sky Survey, within the volume-complete redshift region 0.100 <z < 0.325, for which we construct SZ effect maps by stacking Planck data over the full range of richness. Dividing the sample into richness bins we simultaneously solve for the mean cluster mass in each bin together with the corresponding radial pressure profile parameters, employing an Monte Carlo Markov Chain analysis. These profiles are well detected over a much wider range of cluster mass and radius than previous work, showing a clear trend towards larger break radius with increasing cluster mass. Our SZ-based masses fall ∼16 per cent below the mass–richness relations from weak lensing, in a similar fashion as the 'hydrostatic bias' related with X-ray derived masses. Finally, we derive a tight Y500–M500 relation over a wide range of cluster mass, with a power-law slope equal to 1.70 ± 0.07, which agrees well with the independent slope obtained by the Planck team with an SZ-selected cluster sample, but extends to lower masses with higher precision. [ABSTRACT FROM AUTHOR]

We construct a large, redshift-complete sample of distant galaxy clusters by correlating Sloan Digital Sky Survey Data Release 12 redshifts with clusters identified with the red-sequence Matched-filter Probabilistic Percolation (redMaPPer) algorithm. Our spectroscopic completeness is >97 per cent for ≃7000 clusters within the redMaPPer selection limit, z ≤ 0.325, so that our cluster correlation functions aremuch more precise than earlierwork and not suppressed by uncertain photometric redshifts. We derive an accurate power-law mass-richness relation from the observed abundance with respect to the mass function from Millennium XXL (MXXL) simulations, adjusted to the Planck-weighted cosmology. The number density of clusters is found to decline by 20 per cent over the range 0.1 < z < 0.3, in good agreement with the evolution predicted by MXXL. Our projected 3D correlation function scales with richness, λ, rising from r0 = 14 h-1 Mpc at λ ≃ 25 to r0 = 22 h-1 Mpc at λ ≃ 60, with a gradient that matches MXXL when applying our mass-richness relation, whereas the observed amplitude of the correlation function at (z) = 0.24 exceeds the MXXL prediction by 20 per cent at the ≃2.5σ level. This tension cannot be blamed on spurious, randomly located clusters as this would reduce the correlation amplitude. Full consistency between the correlation function and the abundances is achievable for the pre-Planck values of σ8 = 0.9, Ωm = 0.25 and h = 0.73, matching the improved distance ladder estimate of the Hubble constant. [ABSTRACT FROM AUTHOR]

The massive cluster MACSJ1149.5+2223(z = 0.544) displays five very large lensed images of a well-resolved spiral galaxy at zspect = 1.491. It is within one of these images that the first example of a multiply lensed supernova (SN) has been detected recently as part of the Grism Lens-Amplified Survey from Space. The depth of this data also reveals many H II regions within the lensed spiral galaxy which we identify between the five counter-images. Here, we expand the capability of our free-form method to incorporate these H II regions locally, with other reliable lensed galaxies added for a global solution. This improved accuracy allows us to estimate when the Refsdal SN will appear within the other lensed images of the spiral galaxy to an accuracy of ~7 per cent. We predict this SN will reappear in one of the counter-images (RA = 11:49:36.025, Dec. = +22:23:48.11, J2000) and on 2015 November 1 (with an estimated error of ±25 d) it will be at the same phase as it was when it was originally discovered, offering a unique opportunity to study the early phases of this SN and to examine the consistency of the mass model and the cosmological model that have an impact on the time delay prediction. [ABSTRACT FROM AUTHOR]

We examine the latest data on the clusterMACSJ0717.5+3745 from the Hubble Frontier Fields campaign. The critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. Using our free-form method we obtain an accurate solution, identify here many new sets of multiple images, doubling the number of constraints and improving the reconstruction of the dark matter distribution. Our reconstructed mass map shows several distinct central substructures with shallow density profiles, clarifying earlier work and defining well the relation between the dark matter distribution and the luminous and X-ray peaks within the critically lensed region. Using our free-form method, we are able to meaningfully subtract the mass contribution from cluster members to the deflection field to trace the smoothly distributed cluster dark matter distribution. We find four distinct concentrations, three of which are coincident with the luminous matter. The fourth peak has a significant offset from both the closest luminous and X-ray peaks. These findings, together with dynamical data from the motions of galaxies and gas will be important for uncovering the potentially important implications of this extremely massive and intriguing system. [ABSTRACT FROM AUTHOR]

A clean measurement of the evolution of the galaxy cluster mass function can significantly improve our understanding of cosmology from the rapid growth of cluster masses below z < 0.5. Here, we examine the consistency of cluster catalogues selected from the Sloan Digital Sky Survey by applying two independent gravity-based methods using all available spectroscopic redshifts from the DR10 release. First, we detect a gravitational redshift related signal for 20,119 and 13,128 clusters with spectroscopic redshifts contained in the Gaussian Mixture Brightest Cluster Galaxy (GMBCG) and red-sequence Matched-filter Probabilistic Percolation (redMaPPer) catalogues, respectively, at a level of ~-10 km s-1. This we show is consistent with the magnitude expected using the richness-mass relations provided by the literature and after applying recently clarified relativistic and flux bias corrections. This signal is also consistent with the richest clusters in the larger catalogue of Wen et al., corresponding to M200m ≳ 2 × 1014 M⊙ h-1; however, we find no significant detection of a gravitational redshift signal for lower richness clusters, which may be related to bulk motions from substructure and spurious cluster detections. Secondly, we find all three catalogues generate mass-dependent levels of lensing magnification bias, which enhances the mean redshift of flux-selected background galaxies from the Baryon Oscillation Spectroscopic Survey survey. The magnitude of this lensing effect is generally consistent with the corresponding richness-mass relations advocated for the surveys. We conclude that all catalogues comprise a high proportion of reliable clusters, and that the GMBCG and redMaPPer cluster finder algorithms favour more relaxed clusters with a meaningful gravitational redshift signal, as anticipated by the red-sequence colour selection of the GMBCG and redMaPPer samples. [ABSTRACT FROM AUTHOR]

We present a free-form mass reconstruction of the massive lensing cluster MACS J0416.1−2403 using the latest Hubble Frontier Fields data. Our free-form method finds that the extended lensing pattern is generated by two elongated, closely projected clusters of similar mass. Our lens model identifies new lensed images with which we improve the accuracy of the dark matter distribution. We find that the bimodal mass distribution is nearly coincident with the bimodal X-ray emission, but with the two dark matter peaks lying closer together than the centroids of the X-ray emission. We can reproduce this behaviour with our hydrodynamical model, concluding that the clusters are significantly deflected around each other with the plane of the collision lying close to the line of sight. The projected mass profiles of both subclusters are well constrained in the region 30–165 kpc because of the many interior lensed images, leading to surprisingly flat mass profiles of both components at distances 30–100 kpc from the centre, in agreement with recent simulations of self-interacting dark matter. Using N-body simulations, we discuss the extent to which this may be generated by projection effects in our model as the cores grazeeach other. The relative velocity between the two cores is estimated to be about 1200 km s−1 and mostly along the line of sight so that our simulation is consistent with the relative redshift difference between the two cD galaxies (δz ≈ 0.04). [ABSTRACT FROM AUTHOR]

We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and A383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was ∼1.0 ± 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is ∼0.2 ± 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak-lensing maps of the clusters (in magnitude units, 2.5 log10μ): 0.83 ± 0.16 mag for SN CLO12Car, 0.28 ± 0.08 mag for SN CLN12Did, and 0.43 ± 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications. [ABSTRACT FROM AUTHOR]

Since the discovery of the “Bullet Cluster,” several similar cases have been uncovered that suggest relative velocities well beyond the tail of high speed collisions predicted by the concordance ΛCDM model. However, quantifying such post-merger events with hydrodynamical models requires a wide coverage of possible initial conditions. Here, we show that it is simpler to interpret pre-merger cases, such as A1750, where the gas between the colliding clusters is modestly affected, so that the initial conditions are clear. We analyze publicly available Chandra data confirming a significant increase in the projected X-ray temperature between the two cluster centers in A1750 consistent with our expectations for a merging cluster. We model this system with a self-consistent hydrodynamical simulation of dark matter and gas using the FLASH code. Our simulations reproduce well the X-ray data and the measured redshift difference between the two clusters in the phase before the first core passage viewed at an intermediate projection angle. The deprojected initial relative velocity derived using our model is 1460 km s–1, which is considerably higher than the predicted mean impact velocity for simulated massive haloes derived by recent ΛCDM cosmological simulations, but is within the allowed range. Our simulations demonstrate that such systems can be identified using a multi-wavelength approach and numerical simulations, for which the statistical distribution of relative impact velocities may provide a definitive examination of a broad range of dark matter scenarios. [ABSTRACT FROM AUTHOR]

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]

We show that the fast-moving component of the "Bullet Cluster" (1E0657-56) can induce potentially resolvable redshift differences between multiply lensed images of background galaxies. This moving cluster effect, due to the tangential peculiar velocity of the lens, can be expressed as the scalar product of the lensing deflection angle with the tangential velocity of the mass components; the effect is maximal for clusters colliding in the plane of the sky with velocities boosted by their mutual gravity. The Bullet Cluster is likely to be the best candidate for the first measurement of this effect due to the large collision velocity and because the lensing deflection and the cluster fields can be calculated in advance. We derive the deflection field using multiply lensed background galaxies detected with the Hubble Space Telescope. The velocity field is modeled using self-consistent N-body/hydrodynamical simulations constrained by the observed X-ray and gravitational lensing features of this system. We predict that the triply lensed images of systems "G" and "H" straddling the critical curve of the bullet component will show the largest frequency shifts up to ~0.5 kms-1. These shifts are within the range of the Atacama Large Millimeter/ Submillimeter Array for molecular emission, and are near the resolution limit of the newgeneration high-throughput optical-IR spectrographs. The detection of this effect measures the tangential motion of the subclusters directly, thereby clarifying the tension with ΛCDM, which is inferred from the gas motion less directly. This method may be extended to smaller redshift differences using the Lyα forest toward QSOs lensed by more typical clusters of galaxies. More generally, the tangential component of the peculiar velocities of clusters derived by our method complements the radial component determined by the kinematic Sunyaev-Zel'dovich effect, providing a full three-dimensional description of velocities. [ABSTRACT FROM AUTHOR]

We report the first detection of a redshift-depth enhancement of background galaxies magnified by foreground clusters. Using 300,000 BOSS survey galaxies with accurate spectroscopic redshifts, we measure their mean redshift depth behind four large samples of optically selected clusters from the Sloan Digital Sky Survey (SDSS) surveys, totaling 5000-15,000 clusters. A clear trend of increasing mean redshift toward the cluster centers is found, averaged over each of the four cluster samples. In addition, we find similar but noisier behavior for an independent X-ray sample of 158 clusters lying in the foreground of the current BOSS sky area. By adopting the mass-richness relationships appropriate for each survey, we compare our results with theoretical predictions for each of the four SDSS cluster catalogs. The radial form of this redshift enhancement is well fitted by a richness-to-mass weighted composite Navarro-Frenk-White profile with an effective mass ranging between M200 ~ 1.4-1.8 × 1014M☉ for the optically detected cluster samples, and M200 ~ 5.0 × 1014M☉ for the X-ray sample. This lensing detection helps to establish the credibility of these SDSS cluster surveys, and provides a normalization for their respective mass-richness relations. In the context of the upcoming bigBOSS, Subaru Prime Focus Spectrograph, and EUCLIDNISP spectroscopic surveys, this method represents an independent means of deriving the masses of cluster samples for examining the cosmological evolution, and provides a relatively clean consistency check of weak-lensing measurements, free from the systematic limitations of shear calibration. [ABSTRACT FROM AUTHOR]

ABSTRACT We characterize the typical offset between the dark matter (DM) projected centre and the brightest cluster galaxy (BCG) in 10 000 Sloan Digital Sky Survey clusters. To place constraints on the centre of DM, we use an automated strong lensing (SL) analysis, mass-modelling technique which is based on the well-tested assumption that light traces mass. The cluster galaxies are modelled with a steep power law, and the DM component is obtained by smoothing the galaxy distribution fitting a low-order two-dimensional polynomial (via spline interpolation), while probing a whole range of polynomial degrees and galaxy power laws. We find that the offsets between the BCG and the peak of the smoothed light map representing the DM, Δ, are distributed equally around zero with no preferred direction, and are well described by a log-normal distribution with [ABSTRACT FROM AUTHOR]

ABSTRACT We present results from strong lens modelling of 10 000 Sloan Digital Sky Survey (SDSS) clusters, to establish the universal distribution of Einstein radii. Detailed lensing analyses have shown that the inner mass distribution of clusters can be accurately modelled by assuming light traces mass, successfully uncovering large numbers of multiple images. Approximate critical curves and the effective Einstein radius of each cluster can therefore be readily calculated, from the distribution of member galaxies and scaled by their luminosities. We use a subsample of 10 well-studied clusters covered by both SDSS and Hubble Space Telescope ( HST) to calibrate and test this method, and show that an accurate determination of the Einstein radius and mass can be achieved by this approach 'blindly', in an automated way, and without requiring multiple images as input. We present the results of the first 10 000 clusters analysed in the range 0.1 < z < 0.55 and compare them to theoretical expectations. We find that for this all-sky representative sample the Einstein radius distribution is lognormal in shape, with , , and with higher abundance of large θe clusters than predicted by Λ cold dark matter. We visually inspect each of the clusters with ( zs= 2) and find that ∼20 per cent are boosted by various projection effects detailed here, remaining with ∼40 real giant-lens candidates, with a maximum of ( zs= 2) for the most massive candidate, in agreement with semi-analytic calculations. The results of this work should be verified further when an extended calibration sample is available. [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 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]

We present a strong-lensing analysis of the galaxy cluster MS 1358.4+6245 (), in deep six-band HST/ACS imaging. In addition to the well-studied system at , our modelling method uncovers 19 new multiply lensed images belonging to seven background sources, so that a total of 23 images and their redshifts are used to accurately constrain the inner mass distribution. We derive a relatively shallow inner mass profile, ( kpc), with a much higher magnification than estimated previously by models constrained only by the system. Using these many new images we can apply a non-parametric adaptive-grid method, which also yields a shallow mass profile without prior assumptions, strengthening our conclusions. The total magnification of the galaxy is high, about a times over its four images, so that the inferred source size, luminosity and star formation rate are about times smaller than previous estimates, corresponding to a dwarf-sized galaxy of radius kpc. A detailed image of the interior morphology of the source is generated with a high effective resolution of only 50 pc, thanks to the high magnification and to the declining angular diameter distance above for the standard cosmology, so that this image apparently represents the best resolved object known at high redshift. [ABSTRACT FROM AUTHOR]

ABSTRACT We present the results of a strong-lensing analysis of a complete sample of 12 very luminous X-ray clusters at z > 0.5 using HST/ACS images. Our modelling technique has uncovered some of the largest known critical curves outlined by many accurately predicted sets of multiple images. The distribution of Einstein radii has a median value of ≃ 28 arcsec (for a source redshift of zs∼ 2), twice as large as other lower z samples, and extends to 55 arcsec for MACS J0717.5 +3745, with an impressive enclosed Einstein mass of 7.4 × 1014 M⊙. We find that nine clusters cover a very large area ( > 2.5 arcmin 2) of high magnification ( μ > 10×) for a source redshift of zs∼ 8, providing primary targets for accessing the first stars and galaxies. We compare our results with theoretical predictions of the standard Λ cold dark matter ( ΛCDM) model which we show systematically fall short of our measured Einstein radii by a factor of ≃ 1.4, after accounting for the effect of lensing projection. Nevertheless, a revised analysis, once arc redshifts become available, and similar analyses of larger samples, is needed in order to establish more precisely the level of discrepancy with ΛCDM predictions. [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]

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with ‘overdensities’ of galaxies that are bright in the Lyman-a line of hydrogen. A powerful technique for detecting high-redshift galaxies is to search for the characteristic ‘Lyman break’ feature in the galaxy colour, at wavelengths just shortwards of Lya, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate protocluster, TN J1338-1942 at a redshift z ˜ 4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TN J1338-1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age. [ABSTRACT FROM AUTHOR]

We present results from a comprehensive lensing analysis in Hubble Space Telescope (HST) data of the complete Cluster Lensing And Supernova survey with Hubble cluster sample. We identify previously undiscovered multiple images, allowing improved or first constraints on the cluster inner mass distributions and profiles. We combine these strong lensing constraints with weak lensing shape measurements within the HST field of view (FOV) to jointly constrain the mass distributions. The analysis is performed in two different common parameterizations (one adopts light-traces-mass for both galaxies and dark matter while the other adopts an analytical, elliptical Navarro-Frenk-White form for the dark matter) to provide a better assessment of the underlying systematics—which is most important for deep, cluster-lensing surveys, especially when studying magnified high-redshift objects. We find that the typical (median), relative systematic differences throughout the central FOV are ∼40% in the (dimensionless) mass density, κ, and ∼20% in the magnification, μ. We show maps of these differences for each cluster, as well as the mass distributions, critical curves, and two-dimensional (2D)-integrated mass profiles. For the Einstein radii (zs = 2) we find that all typically agree within 10% between the two models, and Einstein masses agree, typically, within ∼15%. At larger radii, the total projected, 2D-integrated mass profiles of the two models, within r ∼ 2′, differ by ∼30%. Stacking the surface-density profiles of the sample from the two methods together, we obtain an average slope of dlog (Σ)/dlog (r) ∼ –0.64 ± 0.1, in the radial range [5350] kpc. Last, we also characterize the behavior of the average magnification, surface density, and shear differences between the two models as a function of both the radius from the center and the best-fit values of these quantities. All mass models and magnification maps are made publicly available for the community. [ABSTRACT FROM AUTHOR]

The distinctive cometary X-ray morphology of the recently discovered massive galaxy cluster “El Gordo” (ACT-CT J0102–4915; z = 0.87) indicates that an unusually high-speed collision is ongoing between two massive galaxy clusters. A bright X-ray “bullet” leads a “twin-tailed” wake, with the Sunyaev-Zel'dovich (SZ) centroid at the end of the northern tail. We show how the physical properties of this system can be determined using our FLASH-based, N-body/hydrodynamic model, constrained by detailed X-ray, SZ, and Hubble lensing and dynamical data. The X-ray morphology and the location of the two dark matter components and the SZ peak are accurately described by a simple binary collision viewed about 480 million years after the first core passage. We derive an impact parameter of ≃300 kpc, and a relative initial infall velocity of ≃2250 km s–1 when separated by the sum of the two virial radii assuming an initial total mass of 2.15 × 1015M☼ and a mass ratio of 1.9. Our model demonstrates that tidally stretched gas accounts for the northern X-ray tail along the collision axis between the mass peaks, and that the southern tail lies off axis, comprising compressed and shock heated gas generated as the less massive component plunges through the main cluster. The challenge for ΛCDM will be to find out if this physically extreme event can be plausibly accommodated when combined with the similarly massive, high-infall-velocity case of the Bullet cluster and other such cases being uncovered in new SZ based surveys. [ABSTRACT FROM AUTHOR]

We present profiles of temperature, gas mass, and hydrostatic mass estimated from new and archival X-ray observations of CLASH clusters. We compare measurements derived from XMM and Chandra observations with one another and compare both to gravitational lensing mass profiles derived with CLASH Hubble Space Telescope and Subaru Telescope lensing data. Radial profiles of Chandra and XMM measurements of electron density and enclosed gas mass are nearly identical, indicating that differences in hydrostatic masses inferred from X-ray observations arise from differences in gas-temperature measurements. Encouragingly, gas temperatures measured in clusters by XMM and Chandra are consistent with one another at ∼100-200 kpc radii, but XMM temperatures systematically decline relative to Chandra temperatures at larger radii. The angular dependence of the discrepancy suggests that additional investigation on systematics such as the XMM point-spread function correction, vignetting, and off-axis responses is yet required. We present the CLASH-X mass-profile comparisons in the form of cosmology-independent and redshift-independent circular-velocity profiles. We argue that comparisons of circular-velocity profiles are the most robust way to assess mass bias. Ratios of Chandra hydrostatic equilibrium (HSE) mass profiles to CLASH lensing profiles show no obvious radial dependence in the 0.3-0.8 Mpc range. However, the mean mass biases inferred from the weak-lensing (WL) and SaWLens data are different. As an example, the weighted-mean value at 0.5 Mpc is 〈 b〉 = 0.12 for the WL comparison and 〈 b〉 = –0.11 for the SaWLens comparison. The ratios of XMM HSE mass profiles to CLASH lensing profiles show a pronounced radial dependence in the 0.3-1.0 Mpc range, with a weighted mean mass bias value rising to 〈 b〉 ≳ 0.3 at ∼1 Mpc for the WL comparison and 〈 b〉 ≈ 0.25 for the SaWLens comparison. The enclosed gas mass profiles from both Chandra and XMM rise to a value ≈1/8 times the total-mass profiles inferred from lensing at ≈0.5 Mpc and remain constant outside of that radius, suggesting that Mgas × 8 profiles may be an excellent proxy for total-mass profiles at ≳ 0.5 Mpc in massive galaxy clusters. [ABSTRACT FROM AUTHOR]

We discuss how Type Ia supernovae (SNe) strongly magnified by foreground galaxy clusters should be self-consistently treated when used in samples fitted for the cosmological parameters. While the cluster lens magnification of a SN can be well constrained from sets of multiple images of various background galaxies with measured redshifts, its value is typically dependent on the fiducial set of cosmological parameters used to construct the mass model. In such cases, one should not naively demagnify the observed SN luminosity by the model magnification into the expected Hubble diagram, which would create a bias, but instead take into account the cosmological parameters a priori chosen to construct the mass model. We quantify the effect and find that a systematic error of typically a few percent, up to a few dozen percent per magnified SN may be propagated onto a cosmological parameter fit unless the cosmology assumed for the mass model is taken into account (the bias can be even larger if the SN is lying very near the critical curves). We also simulate how such a bias propagates onto the cosmological parameter fit using the Union2.1 sample supplemented with strongly magnified SNe. The resulting bias on the deduced cosmological parameters is generally at the few percent level, if only few biased SNe are included, and increases with the number of lensed SNe and their redshift. Samples containing magnified Type Ia SNe, e.g., from ongoing cluster surveys, should readily account for this possible bias. [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]

We report statistical results for dark matter (DM) velocity anisotropy, β, from a sample of some 6000 cluster-size halos (at redshift zero) identified in a ΛCDM hydrodynamical adaptive mesh refinement simulation performed with the ENZO code. These include profiles of β in clusters with different masses, relaxation states, and at several redshifts, modeled both as spherical and triaxial DM configurations. Specifically, although we find a large scatter in the DM velocity anisotropy profiles of different halos (across elliptical shells extending to at least ∼1.5rvir), universal patterns are found when these are averaged over halo mass, redshift, and relaxation stage. These are characterized by a very small velocity anisotropy at the halo center, increasing outward to ∼0.27 and leveling off at ∼0.2rvir. Indirect measurements of the DM velocity anisotropy fall on the upper end of the theoretically expected range. Though measured indirectly, the estimations are derived by using two different surrogate measurements—X-ray and galaxy dynamics. Current estimates of the DM velocity anisotropy are based on a very small cluster sample. Increasing this sample will allow theoretical predictions to be tested, including the speculation that the decay of DM particles results in a large velocity boost. We also find, in accord with previous works, that halos are triaxial and likely to be more prolate when unrelaxed, whereas relaxed halos are more likely to be oblate. Our analysis does not indicate that there is significant correlation (found in some previous studies) between the radial density slope, γ, and β at large radii, 0.3 rvir < r < rvir. [ABSTRACT FROM AUTHOR]