[en] Since galaxy clusters sit at the high end of the mass function, the number of galaxy clusters both massive and concentrated enough to yield particularly large Einstein radii poses useful constraints on cosmological and structure formation models. To date, less than a handful of clusters are known to have Einstein radii exceeding $\sim <!--\; ???\; -->{40}^{\mathrm{\prime <!--\; ???\; -->}\mathrm{\prime <!--\; ???\; -->}}$ (for a source at $z_s\simeq <!--\; ???\; -->2$, nominally). Here, we report an addition to that list of the Sunyaev–Zel’dovich (SZ) selected cluster, PLCK G287.0+32.9 (z = 0.38), the second-highest SZ-mass (M ₅₀₀) cluster from the Planck catalog. We present the first strong-lensing analysis of the cluster, identifying 20 sets of multiply imaged galaxies and candidates in new Hubble Space Telescope (HST) data, including a long, $l\sim <!--\; ???\; -->{22}^{\mathrm{\prime <!--\; ???\; -->}\mathrm{\prime <!--\; ???\; -->}}$ giant arc, as well as a quadruply imaged, apparently bright (magnified to $J_{\mathrm{F}110\mathrm{W}}=25.3$ AB), likely high-redshift dropout galaxy at $z_{\mathrm{p}\mathrm{h}\mathrm{o}\mathrm{t}}=6.90$ [6.13–8.43] (95% C.I.). Our analysis reveals a very large critical area (1.55 arcmin², $z_s\simeq <!--\; ???\; -->2$), corresponding to an effective Einstein radius of ${\mathrm{\theta <!--\; ??\; -->}}_{\mathrm{E}}\sim <!--\; ???\; -->{42}^{\mathrm{\prime <!--\; ???\; -->}\mathrm{\prime <!--\; ???\; -->}}$. The model suggests the critical area will expand to 2.58 arcmin² (${\mathrm{\theta <!--\; ??\; -->}}_{\mathrm{E}}\sim <!--\; ???\; -->{54}^{\mathrm{\prime <!--\; ???\; -->}\mathrm{\prime <!--\; ???\; -->}}$) for sources at $z_s\sim <!--\; ???\; -->10$. Our work adds to recent efforts to model very massive clusters toward the launch of the James Webb Space Telescope, in order to identify the most useful cosmic lenses for studying the early universe. Spectroscopic redshifts for the multiply imaged galaxies and additional HST data will be necessary for refining the lens model and verifying the nature of the $z\sim <!--\; ???\; -->7$ dropout.

[en] We combine deep Hubble Space Telescope grism spectroscopy with a new Bayesian method to derive maps of gas-phase metallicity for 10 star-forming galaxies at high redshift ($1.2\lesssim <!--\; ???\; -->z\lesssim <!--\; ???\; -->2.3$). Exploiting lensing magnification by the foreground cluster MACS1149.6+2223, we reach sub-kiloparsec spatial resolution and push the limit of stellar mass associated with such high-z spatially resolved measurements below ${10}^8{M}_{\odot <!--\; ???\; -->}$ for the first time. Our maps exhibit diverse morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, and other physical processes that can affect the gas and metallicity distributions in individual galaxies. Based upon an exhaustive sample of all existing sub-kiloparesec resolution metallicity gradient measurements at high z, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk-formation phase can explain the majority of observed metallicity gradients, without involving galactic feedback or radial outflows. We observe a tentative correlation between stellar mass and metallicity gradients, consistent with the “downsizing” galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. In addition to the spatially resolved analysis, we compile a sample of homogeneously cross-calibrated integrated metallicity measurements spanning three orders of magnitude in stellar mass at z ∼ 1.8. We use this sample to study the mass–metallicity relation (MZR) and find that the slope of the observed MZR can rule out the momentum-driven wind model at a 3σ confidence level.

[en] We provide a new observational test for a key prediction of the ΛCDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth. We perform this test by dynamically analyzing 7 galaxy clusters, spanning the redshift range 0.13 < z_c < 0.45 and caustic mass range 0.4-1.5 10¹⁵ h_0.73^-1 M_☉, with an average of 293 spectroscopically confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall region, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, we identify bound galaxies. Out of these galaxies, we identify infalling and accreted halos and estimate their masses and their dynamical states. Using the estimated masses, we derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ∼0.2 and ∼0.7, we find a ∼1σ agreement with ΛCDM expectations based on the Millennium simulations I and II. At low mass ratios, ∼< 0.2, our derived contribution is underestimated since the detection efficiency decreases at low masses, ∼2 × 10¹⁴ h_0.73^-1 M_☉. At large mass ratios, ∼> 0.7, we do not detect halos probably because our sample, which was chosen to be quite X-ray relaxed, is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated

[en] A pressureless scenario for the dark matter (DM) fluid is a widely adopted hypothesis, despite the absence of direct observational evidence. According to general relativity, the total mass-energy content of a system shapes the gravitational potential well, but different test particles perceive this potential in different ways depending on their properties. Cluster galaxy velocities, being << c, depend solely on the gravitational potential, whereas photon trajectories reflect the contributions from the gravitational potential plus a relativistic-pressure term that depends on the cluster mass. We exploit this phenomenon to constrain the equation of state (EoS) parameter of the fluid, primarily DM, contained in galaxy clusters. We use complementary information provided by the kinematic and lensing mass profiles of the galaxy cluster MACS 1206.2–0847 at z = 0.44, as obtained in an extensive imaging and spectroscopic campaign within the Cluster Lensing And Supernova survey with Hubble. The unprecedented high quality of our data set and the properties of this cluster are well suited to determine the EoS parameter of the cluster fluid. Since baryons contribute at most 15% to the total mass in clusters and their pressure is negligible, the EoS parameter we derive describes the behavior of the DM fluid. We obtain the most stringent constraint on the DM EoS parameter to date, w = (p_r + 2 p_t )/(3 c ²ρ) = 0.00 ± 0.15 (stat) ± 0.08 (syst), averaged over the radial range 0.5 Mpc ≤ r ≤ r ₂₀₀, where p_r and p_t are the radial and tangential pressure, and ρ is the density. We plan to further improve our constraint by applying the same procedure to all clusters from the ongoing Cluster Lensing And Supernova Survey with Hubble-Very Large Telescope program

[en] We present high resolution (9″) imaging of the Sunyaev–Zel’dovich Effect (SZE) toward two massive galaxy clusters, MACS J0647.7+7015 (z = 0.591) and MACS J1206.2–0847 (z = 0.439). We compare these 90 GHz measurements, taken with the Multiplexed Squid/TES Array at Ninety Gigahertz (MUSTANG ) receiver on the Green Bank Telescope, with generalized Navarro–Frenk–White (gNFW) models derived from Bolocam 140 GHz SZE data as well as maps of the thermal gas derived from Chandra X-ray observations. We adopt a serial-fitting approach, in which gNFW models are first fit to the Bolocam data and then compared to the MUSTANG data to determine an overall best-fit model. For MACS J0647.7+7015, we find a gNFW profile with core slope parameter γ = 0.9 fits the MUSTANG image with ${\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{r}\mathrm{e}\mathrm{d}}^2=1.005$ and probability to exceed (PTE) = 0.34. For MACS J1206.2–0847, we find $\mathrm{\gamma <!--\; ??\; -->}=0.7$, ${\mathrm{\chi <!--\; ??\; -->}}_{\mathrm{r}\mathrm{e}\mathrm{d}}^2=0.993$, and PTE = 0.70. In addition, we find a significant (>3σ) residual SZE feature in MACS J1206.2–0847 coincident with a group of galaxies identified in Very Large Telescope data and filamentary structure found in a weak-lensing mass reconstruction. We suggest the detected sub-structure may be the SZE decrement from a low mass foreground group or an infalling group. Giant Metrewave Radio Telescope measurements at 610 MHz reveal diffuse extended radio emission to the west, which we posit is either an active galactic nucleus-driven radio lobe, a bubble expanding away from disturbed gas associated with the SZE signal, or a bubble detached and perhaps re-accelerated by sloshing within the cluster. Using the spectroscopic redshifts available, we find evidence for a foreground (z = 0.423) or infalling group, coincident with the residual SZE feature.