1701.02307
Intrinsic alignment of redMaPPer clusters: cluster shape - matter density correlation
van Uitert, Joachimi
Measure the alignment of the shapes of galaxy clusters, as traced by their satellite distributions, with the matter density field using the public redMaPPer catalogue based on SDSS-DR8, which contains 26111 clusters up to z~0.6. The clusters are split into nine redshift and richness samples; in each of them a positive alignment is detected, showing that clusters point towards density peaks. Interpret the measurements within the tidal alignment paradigm, allowing for a richness and redshift dependence. The IA amplitude at the pivot redshift z=0.3 and pivot richness lambda=30 is A_IA^gen = 12.6±1.5. Obtain tentative evidence that the signal increases towards higher richness and lower redshift. The measurements agree well with results of maxBCG clusters and with DM-only sims. Comparing the results to IA measurement of luminosities red galaxies, find that the IA amplitude of galaxy cluster forms a smooth extension towards higher mass. This suggests that these systems share a common alignment mechanism, which can be exploited to improve the physical understanding of IA.
1701.02739
Fast weak lensing simulations with halo model
Giocoli, et al
Full ray-tracing maps of GL, constructed from N-body sims, represent a fundamental tool to interpret present and future WL data. However the limitation of computational resources and storage capabilities severely restrict the number of realisations that can be performed in order to accurately sample both the cosmic shear models and covariance matrices. In this paper, present a halo model formalism for WL that allows to alleviate these issues by producing WL mocks at a reduced computational cost. The model as input the halo population within a desired light-cone and the linear power spectrum of the underlined cosmo model. Examine the contribution given by the presence of substructures within haloes to the cosmic shear power spectrum and quantify it to the percent level. The method allows to reconstruct high-resolution convergence maps, for any desired source redshifts, of light-cones that realistically trace the matter density distribution in the universe, account for masked area and sample selections. Compare the analysis on the same large scale structures constructed using ray-tracing techniques and find very good agreements both in the linear and non-linear regimes up to few percent levels. The accuracy and speed of the method demonstrate the potential of the halo model for WL statistics and the possibility to generate a large sample of convergence maps for different cosmological models as needed for the analysis of large galaxy redshift surveys.
1701.02743
ZOMG II: does the halo assembly history influence central galaxies and gas accretion?
Romano-Diaz, et al
The growth-rate and the internal dynamics of galaxy-sized DM haloes depend on their location within the cosmic web. Haloes that sit at the nodes grow in mass till the present time and are dominated by radial orbits. Using zoom hydrodynamical sims including SF and feedback, study how gas accretes onto these different classes of objects that, for simplicity, dub 'accreting' and 'stalled' haloes. Find that all haloes get a fresh supply of newly accreted gas in their inner regions, although this slowly decreases with time, in particular of the stalled haloes. The inflow of new gas is always higher than (but comparable with) that of recycled material. Overall, the cold-gas fraction increases (decreases) with time for the accreting (stalled) haloes. In all cases, a stellar disc and a bulge form at at the centre of the simulated haloes. The total stellar mass is in excellent agreement with expectations based on the abundance-matching technique. Many properties of the central galaxies do not seem to correlate with the large-scale environment in which the haloes reside. However, there are two notable exceptions that characterize stalled haloes with respect to their accreting counterparts: i) the galaxy disc contains much older stellar populations; ii) its vertical scale-height is larger by a factor of two or more. This thickening is likely due to the heating of the long-lived discs by mergers and close flybys.
1701.02954
Searching for galaxy clusters in the Kilo-Degree Survey
Radovich, et al
Present the tools used to search for galaxy clusters in KiDS, and the first results. The cluster detection is based on an implementation of the optimal filtering technique that enables to identify clusters as over-densities in the distribution of galaxies using their positions on the sky, magnitudes, and photometric redshifts. The contamination and completeness of the cluster catalog are derived using mock catalogs based on the data themselves. The optimal signal to noise threshold for the cluster detection is obtained by randomizing the galaxy positions and selecting the value that produces a contamination of less than 20%. Starting from a subset of clusters detected with high significance at low redshifts, shift them to higher redshifts to estimate the completeness as a function of redshift: the average completeness is ~85%. An estimate of the mass of the clusters is derived using the richness as a proxy. Obtained 1858 candidate clusters with 0<z_c<0.7 and mass 13.5<log(M500/Msun)<15 in an area of 114 eq. degrees (KiDS ESO-DR2). A comparison with publicly available SDSS-based cluster catalogs shows that 50% of the clusters are matched (77% in the case of the redMaPPer catalog). Also cross-matched the cluster catalog with the Abell clusters, and clusters found by XMM and in the Planck-SZ survey; however, only a small number of them lie inside the KiDS area currently available.
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