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Extensive surveys with the Hubble Space Telescope over the past decade, targeting some of the most massive clusters in the sky, have uncovered dozens of galaxy cluster strong lenses. The massive cluster strong-lens scale is typically θE ∼ 10″ to ∼30″–35″, with only a handful of clusters known with Einstein radii θE ∼ 40″ or above (for zsource = 2, nominally). Here we report another very large cluster lens, RXC J0032.1+1808 (z = 0.3956), the second-richest cluster in the redMapper cluster catalog and the 85th most massive cluster in the Planck Sunyaev–Zel'dovich catalog. With our light-traces-mass and fully parametric approaches, we construct strong-lensing models based on 18 multiple images of five background galaxies newly identified in the Hubble data, mainly from the Reionization Lensing Cluster Survey (RELICS), in addition to a known sextuply imaged system in this cluster. Furthermore, we compare these models to Lenstool and GLAFIC models that were produced independently as part of the RELICS program. All models reveal a large effective Einstein radius of θE ≃ 40″ (zsource = 2), owing to the obvious concentration of substructures near the cluster center. Although RXC J0032.1+1808 has a very large critical area and high lensing strength, only three magnified high-redshift candidates are found within the field targeted by RELICS. Nevertheless, we expect many more high-redshift candidates will be seen in wider and deeper observations with Hubble or the James Webb Space Telescope. Finally, the comparison between several algorithms demonstrates that the total error budget is largely dominated by systematic uncertainties. [ABSTRACT FROM AUTHOR]

We used a set of moderately deep and high-resolution optical observations obtained with the Hubble Space Telescope to investigate the properties of the stellar population in the heavily obscured bulge globular cluster (GC) NGC 6256. The analysis of the color–magnitude diagram (CMD) revealed a stellar population with an extended blue horizontal branch severely affected by differential reddening, which was corrected, taking into account color excess variations up to δE(B − V) ∼ 0.51. We implemented a Monte Carlo Markov Chain technique to perform the isochrone fitting of the observed CMD in order to derive the stellar age, the cluster distance, and the average color excess in the cluster direction. Using three different sets of isochrones we found that NGC 6256 is characterized by a very old stellar age around 13.0 Gyr, with a typical uncertainty of ∼0.5 Gyr. We also found an average color excess of E(B − V) = 1.19 and a distance from the Sun of 6.8 kpc. We then derived the cluster gravitational center and measured its absolute proper motion using the Gaia-DR2 catalog. All this was used to back-integrate the cluster orbit in a Galaxy-like potential and measure its integrals of motion. It turned out that NGC 6256 is currently in a low-eccentricity orbit entirely confined within the bulge and its integrals of motion are fully compatible with a cluster purely belonging to the Galaxy native GC population. All these pieces of evidence suggest that NGC 6256 is an extremely old relic of the past history of the Galaxy, formed during the very first stages of its assembly. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Large surveys of galaxy clusters with the Hubble Space Telescope (HST) and Spitzer, including the Cluster Lensing And Supernova survey with Hubble and the Frontier Fields, have demonstrated the power of strong gravitational lensing to efficiently deliver large samples of high-redshift galaxies. We extend this strategy through a wider, shallower survey named RELICS, the Reionization Lensing Cluster Survey, described here. Our 188-orbit Hubble Treasury Program observed 41 clusters at 0.182 ≤ z ≤ 0.972 with Advanced Camera for Surveys (ACS) and WFC3/IR imaging spanning 0.4–1.7 μm. We selected 21 of the most massive clusters known based on Planck PSZ2 estimates and 20 additional clusters based on observed or inferred lensing strength. RELICS observed 46 WFC3/IR pointings (∼200 arcmin2) each with two orbits divided among four filters (F105W, F125W, F140W, and F160W) and ACS imaging as needed to achieve single-orbit depth in each of three filters (F435W, F606W, and F814W). As previously reported by Salmon et al., we discovered over 300 z ∼ 6–10 candidates, including the brightest z ∼ 6 candidates known, and the most distant spatially resolved lensed arc known at z ∼ 10. Spitzer IRAC imaging (945 hr awarded, plus 100 archival, spanning 3.0–5.0 μm) has crucially enabled us to distinguish z ∼ 10 candidates from z ∼ 2 interlopers. For each cluster, two HST observing epochs were staggered by about a month, enabling us to discover 11 supernovae, including 3 lensed supernovae, which we followed up with 20 orbits from our program. Reduced HST images, catalogs, and lens models are available on MAST, and reduced Spitzer images are available on IRSA. [ABSTRACT FROM AUTHOR]

Strong gravitational lensing (SL) is a powerful means of mapping the distribution of dark matter. In this work, we perform an SL analysis of the prominent X-ray cluster RXJ0152.7-1357 (z = 0.83, also known as CL0152.7-1357) in Hubble Space Telescope images, taken in the framework of the Reionization Lensing Cluster Survey (RELICS). On top of a previously known z = 3.93 galaxy multiply imaged by RXJ0152.7-1357, for which we identify an additional multiple image, guided by a light-traces-mass approach, we identify seven new sets of multiply imaged background sources lensed by this cluster, spanning the redshift range [1.79–3.93]. A total of 25 multiple images are seen over a small area of ∼0.4 arcmin2, allowing us to put relatively high-resolution constraints on the inner matter distribution. Although modestly massive, the high degree of substructure, together with its very elongated shape, makes RXJ0152.7-1357 a very efficient lens for its size. This cluster also comprises the third-largest sample of z ∼ 6–7 candidates in the RELICS survey. Finally, we present a comparison of our resulting mass distribution and magnification estimates with those from a Lenstool model. These models are made publicly available through the Mikulski Archive for Space Telescopes. [ABSTRACT FROM AUTHOR]