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Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and pervaded by a diffuse, hot intracluster medium (ICM) that dominates the baryonic content of these systems. The formation and evolution of the ICM across cosmic time 1 is thought to be driven by the continuous accretion of matter from the large-scale filamentary surroundings and energetic merger events with other clusters or groups. Until now, however, direct observations of the intracluster gas have been limited only to mature clusters in the later three-quarters of the history of the Universe, and we have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed. Here we report the detection (about 6 σ ) of the thermal Sunyaev–Zeldovich (SZ) effect 2 in the direction of a protocluster. In fact, the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing the thermal history of cosmic structures 3 . This result indicates the presence of a nascent ICM within the Spiderweb protocluster at redshift z  = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster. Analysis of observations from the Atacama Large Millimeter/submillimeter Array showed evidence of the thermal Sunyaev–Zeldovich effect in the direction of the Spiderweb protocluster at a redshift of 2.156.

Gravitationally magnified images of a faint galaxy from only 500 million years after the Big Bang suggest that galaxies of that age may be the dominant source of the radiation responsible for the re-ionization of the intergalactic medium. A young galaxy captured by a cosmic lens Young galaxies at a cosmic age of less than 500 million years remain largely unexplored because they are at or beyond the sensitivity limits of current large telescopes. This paper reports the use of strong gravitational lensing from a massive cluster of galaxies to observe a galaxy from the early Universe, at a redshift of z ≈ 9.6, equivalent to a cosmic age of approximately 490 million years. The authors suggest that because faint galaxies seem to be abundant at such a young cosmic age they are probably the dominant source for the early re-ionization of the intergalactic medium. 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 1 . 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 2 . 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.

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5 m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 deg2, with at least ∼2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5 m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25% best-seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described here publicly available via the Spitzer Science Center.

Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to ~50. Here we report an image of an individual star at redshift z  = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than ×2,000. A separate image, detected briefly 0.26″ from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of ≳3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars’ light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images’ long-term brightness ratio. An individual star at z  = 1.49 is gravitationally lensed and highly magnified by a foreground galaxy cluster. Fluctuations in the star’s emission provide insight on the mass function of intracluster stars, compact objects and the presence of dark-matter subhaloes.

We present a semi-automatic interactive code, ROma Stellar Spectroscopic Analyzer (ROSSA), to measure radial velocities (RVs) from stellar spectra, covering a broad range of spectral resolutions. The measurement is supported by a graphical interface to change the fitting function (Gaussian or Moffat) and their parameters such as, e.g., symmetry and wings contribution. ROSSA has been applied to the kinematical structure of the Carina dwarf spheroidal galaxy, in order to obtain homogeneous RV measurements of ~1 400 stars collected with various VLT spectrographs (FORS2, FLAMES/GIRAFFE medium- and high-resolution grisms). The spectroscopic targets cover different evolutionary phases and stellar populations of Carina, from the red giant branch to phases of old (horizontal branch) and intermediate age (red clump) helium burning stars. These stars are the tracers of two different star formation episodes (2-6 and 12 Gyr).

We derived stellar ages and metallicities [Z/H] for \\(\\sim\\)70 passive early type galaxies (ETGs) selected from VANDELS survey over the redshift range 1.0$<$$z$$<\\(1.4 and stellar mass range 10\\)<\\(log(M\\)_*\\(/M\\)_\\odot\\()\\)<\\(11.6. We find significant systematics in their estimates depending on models and wavelength ranges considered. Using the full-spectrum fitting technique, we find that both [Z/H] and age increase with mass as for local ETGs. Age and metallicity sensitive spectral indices independently confirm these trends. According to EMILES models, for 67 per cent of the galaxies we find [Z/H]\\)>\\(0.0, a percentage which rises to \\)\\sim\\(90 per cent for log(M\\)_*\\(/M\\)_\\odot\\()\\)>\\(11 where the mean metallicity is [Z/H]=0.17\\)\\pm\\(0.1. A comparison with homogeneous measurements at similar and lower redshift does not show any metallicity evolution over the redshift range 0.0\\(11.0 host stellar populations with [Z/H]>0.05, formed over short timescales (\\)\\Delta{t50}$$<\\(1 Gyr) at early epochs (t\\)_{form}$$<\\(2 Gyr), implying high star formation rates (SFR\\)>\\(100 M\\)_\\odot\\(/yr) in high mass density regions (log(\\)\\Sigma_{1kpc}\\()\\)>\\(10 M\\)_\\odot\\(/kpc\\)^2\\(). This sharp picture tends to blur at lower masses: log(M\\)_*\\(/M\\)_\\odot\\()\\)\\sim\\(10.6 galaxies can host either old stars with [Z/H]\\)<\\(0.0 or younger stars with [Z/H]\\)>\\(0.0, depending on the duration (\\)\\Delta{t50}$) of the SF. The relations between galaxy mass, age and metallicities are therefore largely set up ab initio as part of the galaxy formation process. Mass, SFR and SF time-scale all contribute to shape up the stellar mass-metallicity relation with the mass that modulates metals retention.

From Hubble Frontier Fields photometry, and data from the Multi Unit Spectroscopic Explorer on the Very Large Telescope, we build the Fundamental Plane (FP) relation for the early-type galaxies of the cluster Abell S1063. We use this relation to develop an improved strong lensing model of the total mass distribution of the cluster, determining the velocity dispersions of all 222 cluster members included in the model from their measured structural parameters. Fixing the hot gas component from X-ray data, the mass density distributions of the diffuse dark matter haloes are optimised by comparing the observed and model-predicted positions of 55 multiple images of 20 background sources, distributed over the redshift range \\(0.73-6.11\\). We determine the uncertainties on the model parameters with Monte Carlo Markov chains. Compared to previous works, our model allows for the inclusion of a scatter on the relation between the total mass and the velocity dispersion of cluster members, which also shows a shallower slope. We notice a lower statistical uncertainty on the value of some parameters, such as the core radius, of the diffuse mass component of the cluster. Thanks to a new estimate of the stellar mass of all members, we measure the cumulative projected mass profiles out to a radius of 350 kpc, for all baryonic and dark matter components of the cluster. At the outermost radius, we find a baryon fraction of \\(0.147 \\pm 0.002\\). We compare the sub-haloes as described by our model with recent hydrodynamical cosmological simulations. We find good agreement in terms of the stellar over total mass fraction. On the other hand, we report some discrepancies in terms of the maximum circular velocity, which is an indication of their compactness, and the sub-halo mass function in the central cluster regions.

We present a new weak lensing analysis of the Hubble Frontier Fields galaxy cluster Abell 2744 (\\(z\\) = 0.308) using new Magellan/MegaCam multi-band \\(gri\\) imaging data. We carry out our study by applying brand-new PSF and shape measurement softwares that allow for the use of multi-band data simultaneously, which we first test on Subaru/Suprime-Cam \\(BR_cz'\\) imaging data of the same cluster. The projected total mass of this system within \\(2.35 \\, \\mathrm{Mpc}\\) from the south-west BCG is \\((2.56 \\pm 0.26) \\times 10^{15} \\, \\mathrm{M}_\\odot\\), which makes Abell 2744 one of the most massive clusters known. This value is consistent, within the errors, with previous weak lensing and dynamical studies. Our analysis reveals the presence of three high-density substructures, thus supporting the picture of a complex merging scenario. This result is also confirmed by a comparison with a recent strong lensing study based on high-resolution JWST imaging. Moreover, our reconstructed total mass profile nicely agrees with an extrapolation of the strong lensing best-fit model up to several Mpc from the BCG centre.

James Webb Space Telescope NIRCam images have revealed 154 reliable globular cluster (GC) candidates around the \\(z = 0.0513\\) elliptical galaxy VV~191a after subtracting 34 likely interlopers from background galaxies inside our search area. NIRCam broadband observations are made at 0.9-4.5 \\(\\mu\\)m using the F090W, F150W, F356W, and F444W filters. Using PSF-matched photometry, the data are analyzed to present color-magnitude diagrams (CMDs) and color distributions that suggest a relatively uniform population of GCs, except for small fractions of reddest (5-8%) and bluest (2-4%) outliers. GC models in the F090W vs. (F090-F150W) diagram fit the NIRCam data well and show that the majority of GCs detected have a mass of approximately $\\sim$$10^{6.5}$$M_{\\odot}\\(, with metallicities [Fe/H] spanning the typical range expected for GCs (-2.5\\)\\le\\( [Fe/H]\\)\\le\\( 0.5). However, the models predict \\)\\sim\\(0.3-0.4 mag bluer (F356W-F444W) colors than the NIRCam data for a reasonable range of GC ages, metallicities, and reddening. Although our data does not quite reach the luminosity function turnover, the measured luminosity function is consistent with previous measurements, suggesting an estimated peak at \\)m_{\\rm AB}$$\\sim\\(-9.4 mag, \\)\\pm$0.2 mag in the F090W filter.

The HST treasury program BUFFALO provides extended wide-field imaging of the six Hubble Frontier Fields galaxy clusters. Here we present the combined strong and weak-lensing analysis of Abell 370, a massive cluster at z=0.375. From the reconstructed total projected mass distribution in the 6arcmin x 6arcmin BUFFALO field-of-view, we obtain the distribution of massive substructures outside the cluster core and report the presence of a total of seven candidates, each with mass \\(\\sim 5 \\times 10^{13}M_{\\odot}\\). Combining the total mass distribution derived from lensing with multi-wavelength data, we evaluate the physical significance of each candidate substructure, and conclude that 5 out of the 7 substructure candidates seem reliable, and that the mass distribution in Abell 370 is extended along the North-West and South-East directions. While this finding is in general agreement with previous studies, our detailed spatial reconstruction provides new insights into the complex mass distribution at large cluster-centric radius. We explore the impact of the extended mass reconstruction on the model of the cluster core and in particular, we attempt to physically explain the presence of an important external shear component, necessary to obtain a low root-mean-square separation between the model-predicted and observed positions of the multiple images in the cluster core. The substructures can only account for up to half the amplitude of the external shear, suggesting that more effort is needed to fully replace it by more physically motivated mass components. We provide public access to all the lensing data used as well as the different lens models.