Day 1362

Wednesday.

1801.08001
Curvature from strong gravitational lensing: a spatially closed Universe or systematics?
Li, et al

Model-independent constraints on the spatial curvature are not only closely related to important problems such as the evolution of the Universe and properties of DE, but also provide a test of the validity of the fundamental Copernican principle.  In this paper, with the distance sum rule in the Friedmann-Lemaitre-Robertson-Walker metric, achieve model-independent measurements of the spatial curvature from the latest type Ia SNe and SL observations.  Find that a spatially closed Universe is preferred.  Moreover, by considering different kinds of velocity dispersion and subsample, study possible factors which might affect model-independent estimations for the spatial curvature from SL observations.  It is suggested that the combination of observational data from different surveys might cause a systematic bias and the tension between the spatially flat Universe and SL observations is alleviated when the subsample only from the Sloan Lens ACS Survey is used or a more complex treatment for the density profile of lenses is considered.


1801.08559
The impact of baryons on the matter power spectrum from the Horizon-AGN cosmological hydrodynamical simulation
Chisari, et al

Accurate cosmology from upcoming WL surveys relies on knowledge of the total matter power spectrum at percent level at scales k<10 h/Mpc, for which modeling the impact of baryonic physics is crucial.  Compare measurements of the total matter power spectrum from the Horizon cosmological hydrodynamical simulations.  A DM-only run, one with full baryonic physics, and another lacking AGN feedback.  Baryons cause a suppression of power at k~=10 h/Mpc of <15% at z=0, and an enhancement of a factor of a few at smaller scales due to the more efficient cooling and SF.  The results are sensitive to the presence of the highest mass haloes in the simulation and the distribution of DM is also impacted up to a few percent.  The redshift evolution of the effect is non-monotonic throughout z=0-5 due to an interplay between AGN feedback and gas pressure, and the growth of structure.  Investigate the effectiveness of the "baryonic correction model" proposed by Schneider & Teyssier (2015) in describing the results.  Require a different redshift evolution and propose an alternative fitting function with 4 free parameters that reproduces the results within 5%.  Compared to other simulations, find the impact of baryonic processes on the total matter power spectrum to be smaller at z=0.  Nevertheless, the results also suggest that AGN feedback is not strong enough in the simulation.  Total matter power spectra from the Horizon simulations are made publicly available at https://www.horizon-simulation.org/catalogues.html.


1801.09070
Fast cosmic web simulations with generative adversarial networks
Rodriguez, et al

DM in the universe evolves through gravity to form a complex network of haloes, filaments, sheets and voids, that is known as the cosmic web.  Computational models of the underlying physical processes, such as classical N-body simulations, are extremely resource intensive, as they track the action of gravity in an expanding universe using billions of particles as tracers of the cosmic matter distribution.  Therefore, upcoming cosmology experiments will face a computational bottleneck that may limit the exploitation of their full scientific potential.  To address this challenge, demonstrate the application of a machine learning technique called Generative Adversairal Networks (GAN) to learn models that can efficiently generate new, physical realistic realizations of the cosmic web.  The training set is a small, representative sample of 2D image snapshots from N-body sims of size 500 and 100 Mpc.  Show that the GAN-produced results are qualitatively and quantitatively very similar to the originals.  Generation of a new cosmic web realization with a GAN takes a fraction of a second, compared to the many hours needed by the N-body technique.  Anticipate that GANs will therefore play an important role in providing extremely fast and precise simulations of cosmic web in the era of large cosmological surveys, such as Euclid and LSST.