Extensive Lensing Survey of Optical and Near-infrared Dark Objects (El Sonido): HST H-faint Galaxies behind 101 Lensing Clusters

We present a Spitzer/IRAC survey of H-faint (H 160 ≳ 26.4, < 5σ) sources in 101 lensing cluster fields. Across a CANDELS/Wide-like survey area of ∼648 arcmin2 (effectively ∼221 arcmin2 in the source plane), we have securely discovered 53 sources in the IRAC Channel-2 band (CH2, 4.5 μm; median CH2 = 22.46 ± 0.11 AB mag) that lack robust HST/WFC3-IR F160W counterparts. The most remarkable source in our sample, namely ES-009 in the field of Abell 2813, is the brightest H-faint galaxy at 4.5 μm known so far (CH2 = 20.48 ± 0.03 AB mag). We show that the H-faint sources in our sample are massive (median M star = 1010.3±0.3 M ⊙), star-forming (median star formation rate = 100 − 40 + 60 M ⊙ yr−1), and dust-obscured (A V = 2.6 ± 0.3) galaxies around a median photometric redshift of z = 3.9 ± 0.4. The stellar continua of 14 H-faint galaxies can be resolved in the CH2 band, suggesting a median circularized effective radius (R e,circ; lensing corrected) of 1.9 ± 0.2 kpc and <1.5 kpc for the resolved and whole samples, respectively. This is consistent with the sizes of massive unobscured galaxies at z ∼ 4, indicating that H-faint galaxies represent the dusty tail of the distribution of a wider galaxy population. Comparing with the ALMA dust continuum sizes of similar galaxies reported previously, we conclude that the heavy dust obscuration in H-faint galaxies is related to the compactness of both stellar and dust continua (R e,circ ∼ 1 kpc). These H-faint galaxies make up 16 − 7 + 13 % of the galaxies in the stellar-mass range of 1010 − 1011.2 M ⊙ at z = 3 ∼ 5, contributing to 8 − 4 + 8 % of the cosmic star formation rate density in this epoch and likely tracing the early phase of massive galaxy formation.

Shocks in the stacked Sunyaev–Zel’dovich profiles of clusters – I. Analysis with the Three Hundred simulations

ABSTRACT Gas infalling into the gravitational potential wells of massive galaxy clusters is expected to experience one or more shocks on its journey to becoming part of the intracluster medium (ICM). These shocks are important for setting the thermodynamic properties of the ICM and can therefore impact cluster observables such as X-ray emission and the Sunyaev–Zel’dovich (SZ) effect. We investigate the possibility of detecting signals from cluster shocks in the averaged thermal SZ profiles of galaxy clusters. Using zoom-in hydrodynamic simulations of massive clusters from the Three Hundred Project, we show that if cluster SZ profiles are stacked as a function of R/R200m, shock-induced features appear in the averaged SZ profile. These features are not accounted for in standard fitting formulae for the SZ profiles of galaxy clusters. We show that the shock features should be detectable with samples of clusters from ongoing and future SZ surveys. We also demonstrate that the location of these features is correlated with the cluster accretion rate, as well as the location of the cluster splashback radius. Analyses of ongoing and future surveys, such as SPT-3g, AdvACT, Simons Observatory, and CMB-S4, which include gas shocks will gain a new handle on the properties and dynamics of the outskirts of massive haloes, both in gas and in mass.

The history of metal enrichment traced by X-ray observations of high redshift galaxy clusters

We present the analysis of deep X-ray observations of 10 massive galaxy clusters at redshifts 1.05 &lt; z &lt; 1.71, with the primary goal of measuring the metallicity of the intracluster medium (ICM) at intermediate radii, to better constrain models of the metal enrichment of the intergalactic medium. The targets were selected from X-ray and Sunyaev-Zel’dovich (SZ) effect surveys, and observed with both the XMM-Newton and Chandra satellites. For each cluster, a precise gas mass profile was extracted, from which the value of r500 could be estimated. This allows us to define consistent radial ranges over which the metallicity measurements can be compared. In general, the data are of sufficient quality to extract meaningful metallicity measurements in two radial bins, r &lt; 0.3r500 and 0.3 &lt; r/r500 &lt; 1.0. For the outer bin, the combined measurement for all ten clusters, Z/Z⊙ = 0.21 ± 0.09, represents a substantial improvement in precision over previous results. This measurement is consistent with, but slightly lower than, the average metallicity of 0.315 Solar measured at intermediate-to-large radii in low-redshift clusters. Combining our new high-redshift data with the previous low-redshift results allows us to place the tightest constraints to date on models of the evolution of cluster metallicity at intermediate radii. Adopting a power law model of the form Z∝(1 + z)γ, we measure a slope $\gamma = -0.5^{+0.4}_{-0.3}$, consistent with the majority of the enrichment of the ICM having occurred at very early times and before massive clusters formed, but leaving open the possibility that some additional enrichment in these regions may have occurred since a redshift of 2.

The stellar mass function and evolution of the density profile of galaxy clusters from the Hydrangea simulations at 0 < z < 1.5

ABSTRACT Galaxy clusters are excellent probes to study the effect of environment on galaxy formation and evolution. Along with high-quality observational data, accurate cosmological simulations are required to improve our understanding of galaxy evolution in these systems. In this work, we compare state-of-the-art observational data of massive galaxy clusters ($\gt 10^{14}\, \textrm {M}_{\odot }$) at different redshifts (0 &lt; z &lt; 1.5) with predictions from the Hydrangea suite of cosmological hydrodynamic simulations of 24 massive galaxy clusters ($\gt 10^{14}\, \textrm {M}_{\odot }$ at z = 0). We compare three fundamental observables of galaxy clusters: the total stellar mass-to-halo mass ratio, the stellar mass function, and the radial mass density profile of the cluster galaxies. In the first two of these, the simulations agree well with the observations, albeit with a slightly too high abundance of $M_\star \lesssim 10^{10} \, \mathrm{M}_\odot$ galaxies at z ≳ 1. The Navarro–Frenk–White concentrations of cluster galaxies increase with redshift, in contrast to the decreasing dark matter (DM) halo concentrations. This previously observed behaviour is therefore due to a qualitatively different assembly of the smooth DM halo compared to the satellite population. Quantitatively, we, however, find a discrepancy in that the simulations predict higher stellar concentrations than observed at lower redshifts (z &lt; 0.3), by a factor of ≈2. This may be due to selection bias in the simulations, or stem from shortcomings in the build-up and stripping of their inner satellite halo.

The environment of QSO triplets at 1 ≲ z ≲ 1.5

We present an analysis of the environment of six QSO triplets at 1 ≲ z ≲ 1.5 by analyzing multiband (r, i, z, or g, r, i) images obtained with Megacam at the CFHT telescope, aiming to investigate whether they are associated or not with galaxy protoclusters. This was done by using photometric redshifts trained using the high accuracy photometric redshifts of the COSMOS2015 catalogue. To improve the quality of our photometric redshift estimation, we included in our analysis near-infrared photometry (3.6 and 4.5μm) from the unWISE survey available for our fields and the COSMOS survey. This approach allowed us to obtain good photometric redshifts with dispersion, as measured with the robust σNMAD statistics (which scales as (1 + z)−1), of ∼0.04 for our six fields. Our analysis setup was reproduced on lightcones constructed from the Millennium Simulation data and the latest version of the L-GALAXIES semi-analytic model to verify the protocluster detectability in such conditions. The density field in a redshift slab containing each triplet was then analyzed with a Gaussian kernel density estimator. We did not find any significant evidence of the triplets inhabiting dense structures, such as a massive galaxy cluster or protocluster.