Dark Energy Survey Year 1 Results: Cosmological Constraints from Cluster Abundances, Weak Lensing, and Galaxy Correlations.

We present the first joint analysis of cluster abundances and auto or cross-correlations of three cosmic tracer fields: galaxy density, weak gravitational lensing shear, and cluster density split by optical richness. From a joint analysis (4×2pt+N) of cluster abundances, three cluster cross-correlations, and the auto correlations of the galaxy density measured from the first year data of the Dark Energy Survey, we obtain Ω_{m}=0.305_{-0.038}^{+0.055} and σ_{8}=0.783_{-0.054}^{+0.064}. This result is consistent with constraints from the DES-Y1 galaxy clustering and weak lensing two-point correlation functions for the flat νΛCDM model. Consequently, we combine cluster abundances and all two-point correlations from across all three cosmic tracer fields (6×2pt+N) and find improved constraints on cosmological parameters as well as on the cluster observable-mass scaling relation. This analysis is an important advance in both optical cluster cosmology and multiprobe analyses of upcoming wide imaging surveys.

Detection of Cross-Correlation between Gravitational Lensing and γ Rays.

In recent years, many γ-ray sources have been identified, yet the unresolved component hosts valuable information on the faintest emission. In order to extract it, a cross-correlation with gravitational tracers of matter in the Universe has been shown to be a promising tool. We report here the first identification of a cross-correlation signal between γ rays and the distribution of mass in the Universe probed by weak gravitational lensing. We use data from the Dark Energy Survey Y1 weak lensing data and the Fermi Large Area Telescope 9-yr γ-ray data, obtaining a signal-to-noise ratio of 5.3. The signal is mostly localized at small angular scales and high γ-ray energies, with a hint of correlation at extended separation. Blazar emission is likely the origin of the small-scale effect. We investigate implications of the large-scale component in terms of astrophysical sources and particle dark matter emission.

Detection of CMB-Cluster Lensing using Polarization Data from SPTpol.

We report the first detection of gravitational lensing due to galaxy clusters using only the polarization of the cosmic microwave background (CMB). The lensing signal is obtained using a new estimator that extracts the lensing dipole signature from stacked images formed by rotating the cluster-centered Stokes QU map cutouts along the direction of the locally measured background CMB polarization gradient. Using data from the SPTpol 500 deg^{2} survey at the locations of roughly 18 000 clusters with richness λ≥10 from the Dark Energy Survey (DES) Year-3 full galaxy cluster catalog, we detect lensing at 4.8σ. The mean stacked mass of the selected sample is found to be (1.43±0.40)×10^{14}M_{⊙} which is in good agreement with optical weak lensing based estimates using DES data and CMB-lensing based estimates using SPTpol temperature data. This measurement is a key first step for cluster cosmology with future low-noise CMB surveys, like CMB-S4, for which CMB polarization will be the primary channel for cluster lensing measurements.

Wide-Field Lensing Mass Maps from Dark Energy Survey Science Verification Data.

We present a mass map reconstructed from weak gravitational lensing shear measurements over 139 deg2 from the Dark Energy Survey science verification data. The mass map probes both luminous and dark matter, thus providing a tool for studying cosmology. We find good agreement between the mass map and the distribution of massive galaxy clusters identified using a red-sequence cluster finder. Potential candidates for superclusters and voids are identified using these maps. We measure the cross-correlation between the mass map and a magnitude-limited foreground galaxy sample and find a detection at the 6.8σ level with 20 arc min smoothing. These measurements are consistent with simulated galaxy catalogs based on N-body simulations from a cold dark matter model with a cosmological constant. This suggests low systematics uncertainties in the map. We summarize our key findings in this Letter; the detailed methodology and tests for systematics are presented in a companion paper.

Nonlinear gravitational growth inside and outside the standard cosmology.

We reconsider the problem of nonlinear structure formation inside and outside General Relativity (GR), both in the weakly and strongly nonlinear regime. We show how these regimes can be explored observationally through clustering of high-order cumulants and through the epoch of formation, abundance and clustering of collapse structures, using Press and Schechter (1974, Astrophys. J. 187: 425-438) formalism and its extensions.

The transition to nonlinearity and new constraints on biasing.

We present two new dynamical tests of the biasing hypothesis. The first is based on the amplitude and the shape of the galaxy-galaxy correlation function, xi g(r), where r is the separation of the galaxy pair. The second test uses the mean relative peculiar velocity for galaxy pairs, v12(r). This quantity is a measure of the rate of growth of clustering and it is related to the two-point correlation function for the matter density fluctuations, xi (r). Under the assumption that galaxies trace the mass (xi g = xi), the expected relative velocity can be calculated directly from the observed galaxy clustering. The above assumption can be tested by confronting the expected v12 with direct measurements from velocity-distance surveys. Both our methods are checked against N-body experiments and then compared with the xi g(r) and v12 estimated from the APM galaxy survey and the Mark III catalogue, respectively. Our results suggest that cosmological density parameter is low, omega m approximately 0.3, and that the APM galaxies trace the mass at separations r > or = 5 h-1, where h is the Hubble constant in units of 100 km s-1 Mpc. The present results agree with earlier studies, based on comparing higher-order correlations in the APM with weakly nonlinear perturbation theory. Both approaches constrain the linear bias factor to be within 20% of unity. If the existence of the feature we identified in the APM xi g(r)--the inflection point near xi g = 1--is confirmed by more accurate surveys, we may have discovered gravity's smoking gun: the long awaited "shoulder" in xi, generated by gravitational dynamics and predicted by Gott and Rees 25 years ago.