1606.03092
Consistency of the growth rate in different environments with the 6dF galaxy survey: measurement of the void-galaxy & galaxy-galaxy correlation functions
Achitouv, Blake
Present a new test of gravitational physics by comparing the growth rate of cosmic structure measured around voids with that measured around galaxies in the same large-scale structure dataset, the low-redshift 6-degree Field Galaxy Survey. By fitting a self-consistent RSD model to the 2d g-g and void-galaxy correlation functions, recover growth rate values f\sigma_8=0.36±0.06 and 0.39±0.11, respectively. The environmental-dependence of cosmo statistics can potentially discriminate between modified-gravity scenarios which modulate the growth rate as a function of scale or environment and test the underlying assumptions of homogeneity and isotropy.
1606.03216
Intrinsic alignments in the Illustris simulation
Hilbert, Xu, Schneider, Springer, Vogelsberger, Hernquist
Study IA of galaxy image shapes within Illustris. Investigate how IA correlations depend on observable galaxy properties such as stellar mass, apparent magnitude, redshift, and photometric type, and on the employed shape measurement method. The correlations considered include the matter density-intrinsic ellipticity (mI), galaxy density-intrinsic ellipticity (dI), gravitational shear-intrinsic ellipticity (GI), and intrinsic ellipticity-intrinsic ellipticity (II) correlations. Find stronger correlations for more massive and more luminous galaxies, as well as for earlier photometric types, in agreement with observations. Moreover, shape measurement methods that down-weight the outer parts of galaxy images produce much weaker IA signals on intermediate and large scales than method employing flat radial weights. Thus, the expected contribution of IA to the observed ellipticity correlation in tomographic cosmic shear surveys may be below one percent or several percent of the full signal depending on the details of the shape measurement method. A comparison of the results to a tidal alignment model indicates that such a model is able to reproduce the IA correlations well on intermediate and large scales, provided the effect of varying galaxy density is correctly taken into account. Also find that the GI contributions to the observed ellipticity correlations could be inferred directly from measurements of galaxy density-intrinsic ellipticity correlations, expect on small scales, where systematic differences between mI and dI correlations are large.
1606.03399
Improving photometric redshifts with Ly$\alpha$ tomography
Schmittfull, White
Forming a 3D view of the Universe is a long-standing goal of astronomical observations, and one that becomes increasingly difficult at high z. Discuss how tomography of the IGM at z~2.5 can be used to estimate the z of massive galaxies in a large volume of the Universe based on spectra of galaxies in their background. The method is based on the fact that hierarchical structure formation leads to a strong dependence of the halo density on LS environment. A map of the latter can thus be used to refine the knowledge of the redshifts of haloes and the galaxies and AGN which they host. Show that tomographic maps of the IGM at a resolution of 2.5 Mpc/h can determine the redshifts of more than 90% of massive galaxies with uncertainty of delta(z)/(1+z) = 0.01. Higher resolution maps allow such redshift estimation for lower mass galaxies and haloes.
1606.03407
Weighing the giants V: Galaxy cluster scaling relations
Mantz, et al
Present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust WL measurements. These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses. Constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departure from self-similar scaling laws are primarily limited to cluster cores. However, the data are beginning to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations. Find a positive correlation the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters. While the evolution of the nominal scaling relations is consistent with self similarity, find tentative evidence that the luminosity and temperature scatters respectively decrease and increase with redshift. Physically, this likely related to the development of cool cores and the rate of major mergers. Also examine the scaling relations of redMaPPer richness and Compton Y from Planck. While the richness--mass relation is in excellent agreement with recent work, the measured Y--mass relation departs strongly from that assumed in the Planck cluster cosmology analysis. The latter result is consistent with easier comparisons of lensing and Planck scaling-relation-derived masses.
1606.03892
Higher order moments of lensing convergence - I. Estimate from simulations
Vicinanza, et al
Large area lensing surveys are expected to make it possible to use cosmic shear tomography as a tool to severely constrain cosmo parameters. To this end, one typically relies on second order statistics such as the two-point correlation function and its Fourier counterpart, the power spectrum. Moving a step forward, wonder whether and to which extent higher order statistics can improve the lensing FoM. In this first paper of a series, investigate how second, third and fourth order lensing convergence moments can be measured and use as probe of the underlying cosmo model. Use simulated data and investigate the impact on moments estimate of the map reconstruction procedure, the cosmic variance, and the intrinsic ellipticity noise. Demonstrate that, under realistic assumptions, it is indeed possible to use higher order moments as a further lensing probe.
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