1803.09410
Projection effects of large-scale structures on weak-lensing peak abundances
Yuan, et al
High peaks in WL maps originate dominantly from the lensing effects of single massive haloes. Their abundance is therefore closely related to the halo mass function and thus a powerful cosmological probe. On the other hand, however, besides individual massive halos, LSS along lines of sight also contribute to the peak signals. In this paper, with ray tracing simulations, investigate the LSS projection effects. Show that for current surveys with a large shape noise, the stochastic LSS effects are subdominant. For future WL surveys with source galaxies having a median redshift z_med~1 or higher, however, they are significant. For the cosmological constraints derived from observed WL high peak counts, severe biases can occur if the LSS effects are not taken into account properly. Extend the model of Fan2010 by incorporating the LSS projection effects into the theoretical considerations. By comparing with simulation results, demonstrate the good performance of the improved model and its applicability in cosmological studies.
1803.09463
Gaia: 3-dimensional census of the Milky Way Galaxy
Gilmore
Astrometry from space has unique advantages over ground-based observations: the all-sky coverage, relatively stable, and temperature and gravity invariant operating environment delivers precision, accuracy and sample volume several orders of magnitude greater than ground-based results. Even more importantly, absolute astrometry is possible. The ESA Cornerstone mission Gaia is delivering that promise. Gaia provides 5-D phase space measurements - 3 spatial coordinates and two space motions in the plane of the sky - for a representative sample of the MW's stellar populations, including over two billion stars, being about 1% of the stars over about 50% of the radius. Full 6-D phase space data is delivered from Gaia's line-of-sight (radial) velocities for the 300 million brightest stars. These data make substantial contributions to astrophysics and fundamental physics on scales from the Solar System to Cosmology. A knowledge revolution is underway.
1803.09746
Lenstronomy: multi-purpose gravitational lens modeling software package
Birrer, Amara
Present Lenstronomy, a multi-purpose open-source gravitational lens modeling python package. Lenstronomy is able to reconstruct the lens mass and surface brightness distributions of strong lensing systems using forward modeling. Lenstronomy supports wide range of analytic lens and light models in arbitrary combination. The software is also able to reconstruct complex extended sources (Birrer+2015) as well as being able to model point sources. Lenstronomy was designed to be stable, flexible and numerically accurate, with a clear user interface that could be deployed across different platforms. Throughout its development, have actively used Lenstronomy to make several measurements including deriving constraints on DM properties in strong lenses, measuring the expansion history of the universe with time-delay cosmography, measuring cosmic shear with Einstein rings and decomposing quasar and host galaxy light. The SW is distributed under the MIT license. The documentation, starter guild, example notebooks, source code and installation guidelines can be found at https://lenstronomy.readthdocs.io.
1803.09795
DES Y1 results: validating cosmological parameter estimation using simulated Dark Energy Surveys
MacCrann, et al
Use mock galaxy survey simulations designed to resemble the DES Y1 data to validate and inform cosmological parameter estimation. When similar analysis tools are applied to both simulations and real survey data, they provide powerful validation tests of the DES Y1 cosmo analyses presented in companion papers. Use two suites of galaxy simulations produced using different methods, which therefore provide independent tests of the cosmological parameter inference. The cosmological analysis that is aimed to validate is presented in DES Collaboration+(2017) and uses angular two-point correlation functions of galaxy number counts and WL shear, as well as their cross-correlation, in multiple redshift bins. While the constraints depend on the specific set of simulated realizations available, for both suites of simulations find that the input cosmology is consistent with the combined constraints from multiple simulated DES Y1 realizations in the Omega_m-sigma_8 plane. For one of the suites, able to show with high confidence that any biases in the inferred S8=sigma_8(Omega_m/0.3)^0.5 and Omega_m are smaller than the DES Y1 1sigma uncertainties. For the other suite, for which there are fewer realizations, was unable to be this conclusive; infer a roughly 70% probability that systematic biases in the recovered Omega_m and S8 are sub-dominant to the DES Y1 uncertainty. As cosmological analyses of this kind become increasingly more precise, validation of parameter inference using survey simulations will be essential to demonstrate robustness.
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