1708.04526
OzDES multifire spectroscopy for the Dark Energy Survey: Three year results and first data release
Childress, et al
Present results for the first 3 years of OzDES, a 6-yr program to obtain z for objects in DES SN fields using the 2dF fibre positioned and AAOmega spectrograph on the Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey targeting multiple types of targets at multiple epochs over a multi-year baseline, and is one of the first multi-object spectroscopic surveys to dynamically include transients in to the large list soon after their discovery. At the end of 3 years, OzDES has spectorsopically confirmed almost 100 SNe, and has measured z for 17k objects, including the z of 2,566 SN hosts. Examine how the ability to measure z for targets of various types depends on S/N, magnitude, and exposure time, finding that the z success rate increases singifincatly at a S/N of 2 to 3 per 1-Angstrom bin. Also find that the change in S/N with exposure time closely matches the Poisson limit for stacked exposures as long as 10 hrs. Use these results to predict the z yield of the full OzDES survey, as well as the potential yields of future surveys on other facilities such as the 4mMOST, the Subaru PFS, and the Maunakea Spectroscopic Explorer. This work marks the first OzDES data release, comprising 14,693 redshifts. OzDES is on target to obtain over a yield of approximately 5,700 SN host-galaxy redshifts.
1708.04892
Accurate modeling of galaxy clustering on small scales: testing the standard $\Lambda\mathrm{CDM}$ + halo model
Snha, et al
Interpreting the small-scale clustering of galaxies with halo models can elucidate the connection between galaxies and DM halos. Unfortunately, the modeling is typically not sufficiently accurate for ruling out models in a statistical sense. It is thus difficult to use the information encoded in small scales to test cosmological models or probe subtle features of the galaxy-halo connection. Attempt to push halo modeling into the "accurate" regime with a fully numerical mock-based methodology and careful treatment of statistical and systematic errors. An advantage of this approach is that it can easily incorporate clustering statistic beyond the traditional 2pt statistics. Use this modeling methodology to test the standard LCDM + halo model against the clustering of SDSS DR7 galaxies. Specifically, use the projected correlation function, group multiplicity function and galaxy number density as constraints. Find that while the model provides a good match to each statistic separately, it struggles to fit them jointly. Adding group statistics leads to a more stringent test of the model and significantly tighter constraints on model parameters. Explore the impact of varying the adopted halo definition and cosmological model and find that changing the cosmology makes a significant difference. The most successful model tried (Planck cosmology with Mir halos) matches the clustering of low luminosity galaxies, but exhibits a 2.3 sigma tension with the clustering of luminous galaxies, thus providing evidence that the "standard" halo model needs to be extended. This work represents the most accurate modeling of small-scale clustering to date and opens the door to adding interesting freedom to the halo model and including additional clustering statistics as constraints.
1708.05177
PyCosmo: an integrated cosmological Boltzmann solver
Refregier, Camper, Amara, Heisenberg
As wide-field surveys yield ever more precise measurements, cosmology has entered a phase of high precision requiring highly accurate and fast theoretical predictions. At the heart of most cosmo model predictions is a numerical solution of the EInstein-Boltzmann equations governing the evolution of linear perturbations in the Universe. Present PyCosmo, a new Python based framework to solve this set of equations using a special purpose solver based on symbolic manipulations, automatic generation of C++ code and sparsity optimization. The code uses a consistency relation of the field equations to adapt the time steps and does not rely on physical approximations for speed-up. After reviewing the system of first-order linear homogeneous differential equations to be solved, describe the numerical scheme implemented in PyCosmo. Then compare the predictions and performance of the code for the computation of the transfer functions of cosmological perturbations and compare it to existing cosmological Boltzmann codes. Find that it achieves comparable execution times for comparable accuracies. While PyCosmo does not yet have all the features of other codes, the approach is complementary to existing cosmo Boltzmann solvers and can be used as an independent test of their numerical solutions. The symbolic representation of the Einstein-Boltzmann equation system in PyCosmo provides a convenient interface for implementing extended cosmological models. Also discuss how the PyCosmo framework can also be used as a general framework to compute cosmological quantities as well as observables for both interactive and high-performance batch jobs applications. Information about the PyCosmo package and future code releases are available at www.cosmology.ethz.ch/research/software-lab.html.
No comments:
Post a Comment