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Aiming at comparing different morphological models of galaxy clusters, we use two new methods to make a cosmological model-independent test of the distance-duality (DD) relation. The luminosity distances come from the Union2 compilation of Supernovae Type la. The angular diameter distances are given by two cluster models (De Filippis et al. and Bonamente et al.). The advantage of our methods is that they can reduce statistical errors. Concerning the morphological hypotheses for cluster models, it is mainly focused on the comparison between the elliptical β-model and spherical β-model. The spherical β-model is divided into two groups in terms of different reduction methods of angular diameter distances, i.e., the conservative spherical β -model and corrected spherical β-model. Our results show that the DD relation is consistent with the elliptical β-model at 1σ confidence level (CL) for both methods, whereas for almost all spherical β-model parameterizations, the DD relation can only be accommodated at 3σ CL, particularly for the conservative spherical β-model. In order to minimize systematic uncertainties, we also apply the test to the overlap sample, i.e., the same set of clusters modeled by both De Filippis et al. and Bonamente et al. It is found that the DD relation is compatible with the elliptically modeled overlap sample at 1σ CL; however, for most of the parameterizations the DD relation cannot be accommodated even at 3σ CL for any of the two spherical β-models. Therefore, it is reasonable that the marked triaxial ellipsoidal model is a better geometrical hypothesis describing the structure of the galaxy cluster compared with the spherica β-model if the DD relation is valid in cosmological observations. [ABSTRACT FROM AUTHOR]

We investigate the intracluster light (ICL) in the six Hubble Frontier Field clusters at . We employ a new method, which is free from any functional form of the ICL profile, and exploit the unprecedented depth of this Hubble Space Telescope imaging to map the ICL’s diffuse light out to clustrocentric radii ( mag arcsec−2). From these maps, we construct radial color and stellar mass profiles via SED fitting and find clear negative color gradients in all systems with increasing distance from the Brightest Cluster Galaxy (BCG). While this implies older/more metal-rich stellar components in the inner part of the ICL, we find that the ICL mostly consists of a population, and plausibly originated with cluster galaxies. Furthermore, we find that 10%–15% of the ICL’s mass at large radii ( kpc) lies in a younger/bluer stellar population (∼1 Gyr), a phenomenon not seen in local samples. We attribute this light to the higher fraction of star-forming/(post-)starburst galaxies in clusters at . Ultimately, we find the ICL’s total mass to be –12, constituting 5%–20% of the clusters’ total stellar mass, or about half of the value at . The above implies distinct formation histories for the ICL and BCGs/other massive cluster galaxies; i.e., the ICL at this epoch is still being constructed rapidly ( yr−1), while the BCGs have mostly completed their evolution. To be consistent with the ICL measurements of local massive clusters, such as Virgo, our data suggest mass acquisition mainly from quiescent cluster galaxies is the principal source of ICL material in the subsequent ∼5 Gyr of cosmic time. [ABSTRACT FROM AUTHOR]

Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Survey from Space, we study 2200 cluster and 1748 field galaxies at to determine the impact of environment on galaxy size and structure at stellar masses , an unprecedented limit at these redshifts. Based on simple assumptions——we find no significant differences in half-light radii (re) between equal-mass cluster or field systems. More complex analyses——reveal local density (Σ) to induce only a 7% ± 3% (95% confidence) reduction in re beyond what can be accounted for by U − V color, Sérsic index (n), and redshift (z) effects. Almost any size difference between galaxies in high- and low-density regions is thus attributable to their different distributions in properties other than environment. Indeed, we find a clear color–re correlation in low-mass passive cluster galaxies () such that bluer systems have larger radii, with the bluest having sizes consistent with equal-mass star-forming galaxies. We take this as evidence that large-re low-mass passive cluster galaxies are recently acquired systems that have been environmentally quenched without significant structural transformation (e.g., by ram pressure stripping or starvation). Conversely, ∼20% of small-re low-mass passive cluster galaxies appear to have been in place since . Given the consistency of the small-re galaxies’ stellar surface densities (and even colors) with those of systems more than ten times as massive, our findings suggest that clusters mark places where galaxy evolution is accelerated for an ancient base population spanning most masses, with late-time additions quenched by environment-specific mechanisms mainly restricted to the lowest masses. [ABSTRACT FROM AUTHOR]