Cluster Lensing And Supernova Survey With Hubble Research Articles

Multi-probe analysis of the galaxy cluster CL J1226.9+3332

The precise estimation of the mass of galaxy clusters is a major issue for cosmology. Large galaxy cluster surveys rely on scaling laws that relate cluster observables to their masses. From the high-resolution observations of ∼45 galaxy clusters with the NIKA2 and XMM-Newton instruments, the NIKA2 Sunyaev-Zel’dovich Large Program should provide an accurate scaling relation between the thermal Sunyaev-Zel’dovich effect and the hydrostatic mass. In this paper we present an exhaustive analysis of the hydrostatic mass of the well-known galaxy cluster CL J1226.9+3332, the highest-redshift cluster in the NIKA2 Sunyaev-Zel’dovich Large Program at z = 0.89. We combined the NIKA2 observations with thermal Sunyaev-Zel’dovich data from the NIKA, Bolocam, and MUSTANG instruments and XMM-Newton X-ray observations, and tested the impact of the systematic effects on the mass reconstruction. We conclude that slight differences in the shape of the mass profile can be crucial when defining the integrated mass at R500, which demonstrates the importance of the modelling in the mass determination. We prove the robustness of our hydrostatic mass estimates by showing the agreement with all the results found in the literature. Another key factor for cosmology is the bias of the masses estimated assuming the hydrostatic equilibrium hypothesis. Based on the lensing convergence maps from the Cluster Lensing And Supernova survey with Hubble (CLASH) data, we obtain the lensing mass estimate for CL J1226.9+3332. From this we are able to measure the hydrostatic-to-lensing mass bias for this cluster, which spans from 1 − bHSE/lens ∼ 0.7 to 1, presenting the impact of data sets and mass reconstruction models on the bias.

The LPSZ-CLASH galaxy cluster sample: Combining lensing and hydrostatic mass estimates

Starting from the clusters included in the NIKA sample and in the NIKA2 Sunyaev-Zel’dovich Large Program (LPSZ) we have selected a sample of six common objects with the Cluster Lensing And Supernova survey with Hubble (CLASH) lensing data. For the LPSZ clusters we have at our disposal both high-angular resolution observations of the thermal SZ with NIKA and NIKA2 and X-ray observations with XMM-Newton from which hydrostatic mass estimates can be derived. In addition, the CLASH dataset includes lensing convergence maps that can be converted into lensing estimates of the total mass of the cluster. One-dimensional mass profiles are used to derive integrated mass estimates accounting for systematic effects (data processing, modeling, etc.). Two-dimensional analysis of the maps can reveal substructures in the cluster and, therefore, inform us about the dynamical state of each system. Moreover, we are able to study the hydrostatic mass to lensing mass bias, across different morphology and a range of redshift clusters to give more insight on the hydrostatic mass bias. The analysis presented in this proceeding follows the study discussed in [20].

Molecular gas in CLASH brightest cluster galaxies at z ∼ 0.2 – 0.9

Brightest cluster galaxies (BCGs) are excellent laboratories for the study of galaxy evolution in dense Mpc-scale environments. We used the IRAM-30 m to observe, in CO(1→0), CO(2→1), CO(3→2), or CO(4→3), 18 BCGs at z ∼ 0.2 − 0.9 drawn from the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Our sample includes RX1532, which is our primary target as it is among the BCGs with the highest star formation rate (SFR ≳100 M⊙ yr−1) in the CLASH sample. We unambiguously detected both CO(1→0) and CO(3→2) in RX1532, yielding a large reservoir of molecular gas, MH2 = (8.7 ± 1.1)×1010 M⊙, and a high level of excitation, r31 = 0.75 ± 0.12. A morphological analysis of the Hubble Space Telescope I-band image of RX1532 reveals the presence of clumpy substructures both within and outside the half-light radius re = (11.6 ± 0.3) kpc, similarly to those found independently both in ultraviolet and in Hα in previous works. We tentatively detected CO(1→0) or CO(2→1) in four other BCGs, with molecular gas reservoirs in the range of MH2 = 2 × 1010 − 11 M⊙. For the remaining 13 BCGs, we set robust upper limits of MH2/M⋆ ≲ 0.1, which are among the lowest molecular-gas-to-stellar-mass ratios found for distant ellipticals and BCGs. In comparison with distant cluster galaxies observed in CO, our study shows that RX1532 (MH2/M⋆ = 0.40 ± 0.05) belongs to the rare population of star-forming and gas-rich BCGs in the distant universe. By using the available X-ray based estimates of the central intra-cluster medium entropy, we show that the detection of large reservoirs of molecular gas MH2 ≳ 1010 M⊙ in distant BCGs is possible when the two conditions are met: (i) high SFR and (ii) low central entropy, which favors the condensation and the inflow of gas onto the BCGs themselves, similarly to what has been previously found for some local BCGs.

Shapes and alignments of dark matter haloes and their brightest cluster galaxies in 39 strong lensing clusters

ABSTRACT We study shapes and alignments of 45 dark matter (DM) haloes and their brightest cluster galaxies (BCGs) using a sample of 39 massive clusters from Hubble Frontier Field (HFF), Cluster Lensing And Supernova survey with Hubble (CLASH), and Reionization Lensing Cluster Survey (RELICS). We measure shapes of the DM haloes by strong gravitational lensing, whereas BCG shapes are derived from their light profiles in Hubble Space Telescope images. Our measurements from a large sample of massive clusters presented here provide new constraints on DM and cluster astrophysics. We find that DM haloes are on average highly elongated with the mean ellipticity of 0.482 ± 0.028, and position angles of major axes of DM haloes and their BCGs tend to be aligned well with the mean value of alignment angles of 22.2 ± 3.9 deg. We find that DM haloes in our sample are on average more elongated than their BCGs with the mean difference of their ellipticities of 0.11 ± 0.03. In contrast, the Horizon-AGN cosmological hydrodynamical simulation predicts on average similar ellipticities between DM haloes and their central galaxies. While such a difference between the observations and the simulation may well be explained by the difference of their halo mass scales, other possibilities include the bias inherent to strong lensing measurements, limited knowledge of baryon physics, or a limitation of cold DM.

K-CLASH: Strangulation and ram pressure stripping in galaxy cluster members at 0.3 < z < 0.6

ABSTRACT Galaxy clusters have long been theorized to quench the star formation of their members. This study uses integral-field unit observations from the K-band MultiObject Spectrograph (KMOS) – Cluster Lensing And Supernova survey with Hubble (CLASH) survey (K-CLASH) to search for evidence of quenching in massive galaxy clusters at redshifts 0.3 < z < 0.6. We first construct mass-matched samples of exclusively star-forming cluster and field galaxies, then investigate the spatial extent of their H α emission and study their interstellar medium conditions using emission line ratios. The average ratio of H α half-light radius to optical half-light radius ($r_{\mathrm{e}, {\rm {H}\,\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$) for all galaxies is 1.14 ± 0.06, showing that star formation is taking place throughout stellar discs at these redshifts. However, on average, cluster galaxies have a smaller $r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$ ratio than field galaxies: 〈$r_{\mathrm{e}, {\rm {H}\alpha }}/r_{\mathrm{e}, R_{\mathrm{c} } }$〉 = 0.96 ± 0.09 compared to 1.22 ± 0.08 (smaller at a 98 per cent credibility level). These values are uncorrected for the wavelength difference between H α emission and Rc-band stellar light but implementing such a correction only reinforces our results. We also show that whilst the cluster and field samples follow indistinguishable mass–metallicity (MZ) relations, the residuals around the MZ relation of cluster members correlate with cluster-centric distance; galaxies residing closer to the cluster centre tend to have enhanced metallicities (significant at the 2.6σ level). Finally, in contrast to previous studies, we find no significant differences in electron number density between the cluster and field galaxies. We use simple chemical evolution models to conclude that the effects of disc strangulation and ram-pressure stripping can quantitatively explain our observations.

The Radial Acceleration Relation in CLASH Galaxy Clusters

Abstract The radial acceleration relation (RAR) in galaxies describes a tight empirical scaling law between the total acceleration observed in galaxies and that expected from their baryonic mass , with a characteristic acceleration scale of m s−2. Here, we examine if such a correlation exists in galaxy clusters using weak-lensing, strong-lensing, and X-ray data sets available for 20 high-mass clusters targeted by the Cluster Lensing And Supernova survey with Hubble (CLASH). By combining our CLASH data with stellar mass estimates for the brightest cluster galaxies (BCGs) and accounting for the stellar baryonic component in clusters, we determine, for the first time, an RAR on BCG–cluster scales. The resulting RAR is well described by a tight power-law relation, , with lognormal intrinsic scatter of . The slope is consistent with the low acceleration limit of the RAR in galaxies, , whereas the intercept implies a much higher acceleration scale of m s−2, indicating that there is no universal RAR that holds on all scales from galaxies to clusters. We find that the observed RAR in CLASH clusters is consistent with predictions from a semianalytical model developed in the standard ΛCDM framework. Our results also predict the presence of a baryonic Faber–Jackson relation ( ) on cluster scales.

K-CLASH: spatially resolving star-forming galaxies in field and cluster environments at z ≈ 0.2–0.6

ABSTRACT We present the KMOS-CLASH (K-CLASH) survey, a K-band Multi-Object Spectrograph (KMOS) survey, of the spatially resolved gas properties and kinematics of 191 (pre-dominantly blue) H α-detected galaxies at 0.2 ≲ z ≲ 0.6 in field and cluster environments. K-CLASH targets galaxies in four Cluster Lensing And Supernova survey with Hubble (CLASH) fields in the KMOS IZ-band, over 7 arcmin radius (≈2–3 Mpc) fields of view. K-CLASH aims to study the transition of star-forming galaxies from turbulent, highly star-forming disc-like and peculiar systems at z ≈ 1–3, to the comparatively quiescent, ordered late-type galaxies at z ≈ 0, and to examine the role of clusters in the build-up of the red sequence since z ≈ 1. In this paper, we describe the K-CLASH survey, present the sample, and provide an overview of the K-CLASH galaxy properties. We demonstrate that our sample comprises star-forming galaxies typical of their stellar masses and epochs, residing both in field and cluster environments. We conclude K-CLASH provides an ideal sample to bridge the gap between existing large integral-field spectroscopy surveys at higher and lower redshifts. We find that star-forming K-CLASH cluster galaxies at intermediate redshifts have systematically lower stellar masses than their star-forming counterparts in the field, hinting at possible ‘downsizing’ scenarios of galaxy growth in clusters at these epochs. We measure no difference between the star formation rates of H α-detected, star-forming galaxies in either environment after accounting for stellar mass, suggesting that cluster quenching occurs very rapidly during the epochs probed by K-CLASH, or that star-forming K-CLASH galaxies in clusters have only recently arrived there, with insufficient time elapsed for quenching to have occurred.

Gas Density Perturbations in the Cool Cores of CLASH Galaxy Clusters

We present a systematic study of gas density perturbations in cool cores of high-mass galaxy clusters. We select 12 relaxed clusters from the Cluster Lensing And Supernova survey with Hubble (CLASH) sample and analyze their cool core features observed with the Chandra X-ray Observatory. We focus on the X-ray residual image characteristics after subtracting their global profile of the X-ray surface brightness distribution. We find that all the galaxy clusters in our sample have, at least, both one positive and one negative excess regions in the X-ray residual image, indicating the presence of gas density perturbations. We identify and characterize the locally perturbed regions using our detection algorithm, and extract X-ray spectra of the intracluster medium (ICM). The ICM temperature in the positive excess region is lower than that in the negative excess region, whereas the ICM in both regions is in pressure equilibrium in a systematic manner. These results indicate that gas sloshing in cool cores takes place in more than 80% of relaxed clusters (95% CL). We confirm this physical picture by analyzing synthetic X-ray observations of a cool-core cluster from a hydrodynamic simulation, finding that our detection algorithm can accurately extract both the positive and negative excess regions and can reproduce the temperature difference between them. Our findings support the picture that the gas density perturbations are induced by gas sloshing, and a large fraction of cool-core clusters have undergone gas sloshing, indicating that gas sloshing may be capable of suppressing runaway cooling of the ICM.

RELICS: The Reionization Lensing Cluster Survey and the Brightest High-z Galaxies

Abstract Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here the candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ≈200 arcmin2. These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ∼ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ∼ 6 candidates are as bright as AB mag ∼23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope.

Strong lensing models of eight CLASH clusters from extensive spectroscopy: Accurate total mass reconstructions in the cores

We carried out a detailed strong lensing analysis of a sub-sample of eight galaxy clusters of the Cluster Lensing And Supernova survey with Hubble (CLASH) in the redshift range of zcluster = [0.23 − 0.59] using extensive spectroscopic information, primarily from the Multi Unit Spectroscopic Explorer (MUSE) archival data and complemented with CLASH-VLT redshift measurements. The observed positions of the multiple images of strongly lensed background sources were used to constrain parametric models describing the cluster total mass distributions. Different models were tested in each cluster depending on the complexity of its mass distribution and on the number of detected multiple images. Four clusters show more than five spectroscopically confirmed multiple image families. In this sample, we did not make use of families that are only photometrically identified in order to reduce model degeneracies between the values of the total mass of a cluster source redshifts, in addition to systematics due to the potential misidentifications of multiple images. For the remaining four clusters, we used additional families without any spectroscopic confirmation to increase the number of strong lensing constraints up to the number of free parameters in our parametric models. We present spectroscopic confirmation of 27 multiply lensed sources, with no previous spectroscopic measurements, spanning over the redshift range of zsrc = [0.7 − 6.1]. Moreover, we confirm an average of 48 galaxy members in the core of each cluster thanks to the high efficiency and large field of view of MUSE. We used this information to derive precise strong lensing models, projected total mass distributions, and magnification maps. We show that, despite having different properties (i.e. number of mass components, total mass, redshift, etc.), the projected total mass and mass density profiles of all clusters have very similar shapes when rescaled by independent measurements of M200c and R200c. Specifically, we measured the mean value of the projected total mass of our cluster sample within 10 (20)% of R200c to be 0.13 (0.32) of M200c, with a remarkably small scatter of 5 (6)%. Furthermore, the large number of high-z sources and the precise magnification maps derived in this work for four clusters add up to the sample of high-quality gravitational telescopes to be used to study the faint and distant Universe.

Multiband Galaxy Morphologies for CLASH: A Convolutional Neural Network Transferred from CANDELS

We present visual-like morphologies over 16 photometric bands, from ultraviolet to near-infrared, for 8412 galaxies in the Cluster Lensing And Supernova survey with Hubble (CLASH) obtained using a convolutional neural network (ConvNet) model. Our model follows the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) main morphological classification scheme, obtaining the probability for each galaxy at each CLASH band of being spheroid, disk, irregular, point source, or unclassifiable. Our catalog contains morphologies for each galaxy with Hmag < 24.5 in every filter where the galaxy is observed. We trained an initial ConvNet model using approximately 7500 expert eyeball labels from CANDELS. We created eyeball labels for 100 randomly selected galaxies per each of the 16-filter set of CLASH (1600 galaxy images in total), where each image was classified by at least five of us. We use these labels to fine-tune the network to accurately predict labels for the CLASH data and to evaluate the performance of our model. We achieve a root-mean-square error of 0.0991 on the test set. We show that our proposed fine-tuning technique reduces the number of labeled images needed for training, as compared to directly training over the CLASH data, and achieves a better performance. This approach is very useful to minimize eyeball labeling efforts when classifying unlabeled data from new surveys. This will become particularly useful for massive data sets such as those coming from near-future surveys such as EUCLID or the LSST. Our catalog consists of prediction of probabilities for each galaxy by morphology in their different bands and is made publicly available at http://www.inf.udec.cl/~guille/data/Deep-CLASH.csv.

On the Origin of the Scatter in the Red Sequence: An Analysis of Four CLASH Clusters

Abstract In clusters of galaxies, the red sequence is believed to be a consequence of a correlation between stellar mass and chemical abundances, with more massive galaxies being more metal-rich and, as a consequence, redder. However, there is a color scatter around the red sequence that holds even with precision photometry, implying that the galaxy population is more complicated than as described by a mass–metallicity relation. We use precision photometry from the Cluster Lensing and Supernova survey with Hubble (CLASH) to investigate what drives this scatter. In four CLASH clusters at z = 0.355 ± 0.007, we find that the optical–IR galaxy colors confirm the previously known trend of metallicity along the red sequence but also show a strong connection between stellar age and red sequence offset, with ages ranging from 3 to 8 Gyr. Starting with fixed-age color–magnitude relations motivated by the mass–metallicity correlations of CLASH cluster galaxies, and by adjusting galaxy colors through stellar population models to put them all at the age of our red sequence, we are able to reduce the, e.g., F625W–F814W scatter from 0.051 to 0.026 mag with median photometric errors of 0.029 mag. While we will extend this analysis to the full CLASH sample, in four clusters our technique already provides a color precision in near-total-light apertures to resolve the spread in stellar population formation ages that drives the scatter in the red sequence.

Constraints on the Mass, Concentration, and Nonthermal Pressure Support of Six CLASH Clusters from a Joint Analysis of X-Ray, SZ, and Lensing Data

Abstract We present a joint analysis of Chandra X-ray observations, Bolocam thermal Sunyaev–Zel’dovich (SZ) effect observations, Hubble Space Telescope (HST) strong-lensing data, and HST and Subaru Suprime-Cam weak-lensing data. The multiwavelength data set is used to constrain parametric models for the distribution of dark and baryonic matter in a sample of six massive galaxy clusters selected from the Cluster Lensing And Supernova survey with Hubble (CLASH). For five of the six clusters, the multiwavelength data set is well described by a relatively simple model that assumes spherical symmetry, hydrostatic equilibrium, and entirely thermal pressure support. The joint analysis yields considerably better constraints on the total mass and concentration of the clusters compared to analysis of any one data set individually. The resulting constraints are consistent with simulation-based predictions for the concentration–mass relation. The subsample of five galaxy clusters is used to place an upper limit on the fraction of pressure support in the intracluster medium (ICM) due to nonthermal processes, such as turbulence and bulk flow of the gas. We constrain the nonthermal pressure fraction at r 500c to be &lt;0.11 at 95% confidence. This is in tension with state-of-the-art hydrodynamical simulations, which predict a nonthermal pressure fraction of ≈0.25 at r 500c for clusters of similar mass and redshift. This tension may be explained by the sample selection and/or our assumption of spherical symmetry.

CLUMP-3D: Testing ΛCDM with Galaxy Cluster Shapes

Abstract The ΛCDM model of structure formation makes strong predictions on the concentration and shape of dark matter (DM) halos, which are determined by mass accretion processes. Comparison between predicted shapes and observations provides a geometric test of the ΛCDM model. Accurate and precise measurements needs a full three-dimensional (3D) analysis of the cluster mass distribution. We accomplish this with a multi-probe 3D analysis of the X-ray regular Cluster Lensing and Supernova survey with Hubble (CLASH) clusters combining strong and weak lensing, X-ray photometry and spectroscopy, and the Sunyaev–Zel’dovich effect (SZe). The cluster shapes and concentrations are consistent with ΛCDM predictions. The CLASH clusters are randomly oriented, as expected given the sample selection criteria. Shapes agree with numerical results for DM-only halos, which hints at baryonic physics being less effective in making halos rounder.

JVLA 1.5 GHz Continuum Observation of CLASH Clusters. I. Radio Properties of the BCGs

We present high-resolution ($\sim 1"$), 1.5 GHz continuum observations of the brightest cluster galaxies (BCGs) of 13 CLASH (Cluster Lensing And Supernova survey with Hubble) clusters at $0.18<z<0.69$ with the Karl G. Jansky Very Large Array (JVLA). Radio emission is clearly detected and characterized for 11 BCGs, while for two of them we obtain only upper limits to their radio flux ($<0.1$ mJy at 5$\sigma$ confidence level). We also consider five additional clusters whose BCG is detected in FIRST or NVSS. We find radio powers in the range from $2\times 10^{23}$ to $\sim 10^{26}$ $W~Hz^{-1}$ and radio spectral indices $\alpha_{1.5}^{30}$ (defined as the slope between 1.5 and 30 GHz) distributed from $\sim -1$ to $-0.25$ around the central value $\langle \alpha \rangle= - 0.68$. The radio emission from the BCGs is resolved in three cases (Abell 383, MACS J1931, and RX J2129), and unresolved or marginally resolved in the remaining eight cases observed with JVLA. In all the cases the BCGs are consistent with being powered by active galactic nuclei (AGN). The radio power shows a positive correlation with the BCG star formation rate, and a negative correlation with the central entropy of the surrounding intracluster medium (ICM) except in two cases (MACS J1206 and CL J1226). Finally, over the restricted range in radio power sampled by the CLASH BCGs, we observe a significant scatter between the radio power and the average mechanical power stored in the ICM cavities.

Calibrating thePlanckcluster mass scale with CLASH

We determine the mass scale ofPlanckgalaxy clusters using gravitational lensing mass measurements from the Cluster Lensing And Supernova survey withHubble(CLASH). We have compared the lensing masses to thePlanckSunyaev-Zeldovich (SZ) mass proxy for 21 clusters in common, employing a Bayesian analysis to simultaneously fit an idealized CLASH selection function and the distribution between the measured observables and true cluster mass. We used a tiered analysis strategy to explicitly demonstrate the importance of priors on weak lensing mass accuracy. In the case of an assumed constant bias,bSZ, between true cluster mass,M500, and thePlanckmass proxy,MPL, our analysis constrains 1−bSZ= 0.73 ± 0.10 when moderate priors on weak lensing accuracy are used, including a zero-mean Gaussian with standard deviation of 8% to account for possible bias in lensing mass estimations. Our analysis explicitly accounts for possible selection bias effects in this calibration sourced by the CLASH selection function. Our constraint on the cluster mass scale is consistent with recent results from the Weighing the Giants program and the Canadian Cluster Comparison Project. It is also consistent, at 1.34σ, with the value needed to reconcile thePlanckSZ cluster counts withPlanck’s base ΛCDM model fit to the primary cosmic microwave background anisotropies.

CLASH: accurate photometric redshifts with 14 HST bands in massive galaxy cluster cores

We present accurate photometric redshifts for galaxies observed by the Cluster Lensing and Supernova survey with Hubble (CLASH). CLASH observed 25 massive galaxy cluster cores with the Hubble Space Telescope in 16 filters spanning 0.2 - 1.7 $\mu$m. Photometry in such crowded fields is challenging. Compared to our previously released catalogs, we make several improvements to the photometry, including smaller apertures, ICL subtraction, PSF matching, and empirically measured uncertainties. We further improve the Bayesian Photometric Redshift (BPZ) estimates by adding a redder elliptical template and by inflating the photometric uncertainties of the brightest galaxies. The resulting photometric redshift accuracies are dz/(1+z) $\sim$ 0.8\%, 1.0\%, and 2.0\% for galaxies with I-band F814W AB magnitudes $<$ 18, 20, and 23, respectively. These results are consistent with our expectations. They improve on our previously reported accuracies by a factor of 4 at the bright end and a factor of 2 at the faint end. Our new catalog includes 1257 spectroscopic redshifts, including 382 confirmed cluster members. We also provide stellar mass estimates. Finally, we include lensing magnification estimates of background galaxies based on our public lens models. Our new catalog of all 25 CLASH clusters is available via MAST. The analysis techniques developed here will be useful in other surveys of crowded fields, including the Frontier Fields and surveys carried out with J-PAS and JWST.

A Multiply-Imaged z ∼ 6.3 Lyman Alpha Emitter candidate behind Abell 2261

While the Lyman-$\alpha$ ($\mathrm{Ly}\alpha$) emission line serves as an important tool in the study of galaxies at $z\lesssim 6$, finding Ly$\alpha$ emitters (LAE) at significantly higher redshifts has been more challenging, probably because of the increasing neutrality of the intergalactic medium above $z\sim6$. Galaxies with extremely high rest-frame Ly$\alpha$ equivalent widths, EW(Ly$\alpha$) $\gtrsim 150$ \AA{}, at $z>6$ are good candidates for Ly$\alpha$ follow-up observations, and can stand out in multiband imaging surveys because of their unusual colors. We have conducted a photometric search for such objects in the Cluster Lensing And Supernova survey with Hubble (CLASH), and report here the identification of three likely gravitationally-lensed images of a single LAE candidate at $z\sim6.3$, behind the galaxy cluster Abell 2261($z = 0.225$). In the process, we also measured with Keck/MOSFIRE the first spectroscopic redshift of a multiply-imaged galaxy behind Abell 2261, at $z = 3.337$. This allows us to calibrate the lensing model, which in turn is used to study the properties of the candidate LAE. Population III galaxy spectral energy distribution (SED) model fits to the CLASH broadband photometry of the possible LAE provide a slightly better fit than Population I/II models. The best fitted model suggests intrinsic EW(Ly$\alpha$) $\approx 160$ \AA{} after absorption in the interstellar and intergalactic medium. Future spectroscopic observations will examine this prediction as well as shed more light on the morphology of this object, which indicates it may be a merger of two smaller galaxies.

M32 Analogs? A Population of Massive Ultra-compact Dwarf and Compact Elliptical Galaxies in Intermediate-redshift Clusters

Abstract We report the discovery of relatively massive, M32-like ultra compact dwarf (UCD) and compact elliptical (CE) galaxy candidates in massive galaxy clusters imaged by the Cluster Lensing And Supernova survey with Hubble (CLASH) survey. Examining the nearly unresolved objects in the survey, we identify a sample of compact objects concentrated around the cluster central galaxies with colors similar to cluster red sequence galaxies. Their colors and magnitudes suggest stellar masses around . More than half of these galaxies have half-light radii smaller than 200 pc, falling into the category of massive UCDs and CEs, with properties similar to M32. The properties are consistent with a tidal stripping origin, but we cannot rule out the possibility that they are early-formed compact objects trapped in massive dark matter halos. The 17 CLASH clusters studied in this work on average contain 2.7 of these objects in their central 0.3 Mpc and 0.6 in their central 50 kpc. Our study demonstrates the possibility of statistically characterizing UCDs/CEs with a large set of uniform imaging survey data.

CLASH-VLT: testing the nature of gravity with galaxy cluster mass profiles

We use high-precision kinematic and lensing measurements of the total mass profile of the dynamically relaxed galaxy cluster MACS J1206.2-0847 at z=0.44 to estimate the value of the ratio η=Ψ/Φ between the two scalar potentials in the linear perturbed Friedmann-Lemaitre-Robertson-Walker metric. An accurate measurement of this ratio, called anisotropic stress, could show possible, interesting deviations from the predictions of the theory of General Relativity, according to which Ψ should be equal to Φ. Complementary kinematic and lensing mass profiles were derived from exhaustive analyses using the data from the Cluster Lensing And Supernova survey with Hubble (CLASH) and the spectroscopic follow-up with the Very Large Telescope (CLASH-VLT). Whereas the kinematic mass profile tracks only the time-time part of the perturbed metric (i.e. only Φ), the lensing mass profile reflects the contribution of both time-time and space-space components (i.e. the sum Φ+Ψ). We thus express η as a function of the mass profiles and perform our analysis over the radial range 0.5 Mpc≤ r≤ r200=1.96 Mpc. Using a spherical Navarro-Frenk-White mass profile, which well fits the data, we obtain η(r200)=1.01 −0.28+0.31 at the 68% C.L. We discuss the effect of assuming different functional forms for mass profiles and of the orbit anisotropy in the kinematic reconstruction. Interpreting this result within the well-studied f(R) modified gravity model, the constraint on η translates into an upper bound to the interaction length (inverse of the scalaron mass) smaller than 2 Mpc. This tight constraint on the f(R) interaction range is however substantially relaxed when systematic uncertainties in the analysis are considered. Our analysis highlights the potential of this method to detect deviations from general relativity, while calling for the need of further high-quality data on the total mass distribution of clusters and improved control on systematic effects.