Day 980

Friday.


1510.00019
Gaussianisation for fast and accurate inference from cosmological data
Schuhmann, Joachimi, Peiris

Present a method to transform multivariate unimodal non-Gaussian posterior probability densities into approximately Gaussian ones via non-linear mappings, such as Box-Cox transformations and generalizations thereof.  This permits an analytical reconstruction of the posterior from a point sample, like a Markov chain, and simplifies the subsequent joint analysis with other experiments.  This way, a multivariate poster density can be reported efficiently, by compressing the information contained in MCMC samples.  Further, the model evidence integral (i.e., the marginal likelihood) can be computed analytically.  This method is analogous to the search for normal parameters in the CMB, but is more general.  The search for the optimally Gaussianising transformation is performed computationally through a maximum-likelihood formalism; its quality an be judged by how well the credible regions of the posterior are reproduced.  Demonstrate that the method outperforms kernel density estimates in this objective.  Further, select marginal posterior samples from Planck data with several distinct strongly non-Gaussian features, and verify the reproduction of the marginal contours.  To demonstrate evidence computation, Gaussianise the joint distribution of data from WL and BAO, for different cosmo models, and find a preference for flat LCDM.  Comparing to values computed with Savage-Dickey density ratio, and Population Monte Carlo, find good agreement of the method within the spread of the other two.


1510.00227
The True origin of Wolf-Rayed stars
Vink

The WR phenomenon is widespread in astronomy.  It involves classical WRs, very massive stars (VMS), WR central stars of planetary nebula CSPN [WRs], and SNe.  But what is the root cause for a certain type of object to turn int on emission-line star?  In this contribution, discuss the basic aspects of radiation-driven winds that might reveal the ultimate difference between WR stars and canonical O-type stars.  Discuss the aspects of (i) weld-enrichment via CNO elements, (ii) high effective temperatures Teff, (iii) an increase in the He abundance Y, and finally (iv) the Eddington factor Gamma.  Over the last couple of years, made a breakthrough in the understanding of Gamma-dependent mass loss, which will have far-reaching consequences for the evolution and fate of the most massive stars in the Universe.  Finally, discuss the prospects for studies of the WR phenomenon in the highest redshift Ly-alpha and He II emitting galaxies.


1510.00242
Compound lensing: Einstein Zig-Zags and high multiplicity lensed images
Collett, Bacon

Compound strong gravitational lensing is a rare phenomenon, but a handful of such lensed systems are likely to be discovered in forthcoming surveys.  In this work, use a double SIS lens model to analytically understand how the properties of the system impact image multiplicity for the final source.  Find that up to six images of a background source can form, but only if the second lens is multiply imaged by the first and the Einstein radius of the second lens is comparable to, but does not exceed that of the first.  Then build a model of compound lensing masses in the Universe, using SIE lenses, and assess how the optical depth for multiple imaging by a galaxy-galaxy compound lens varies with source redshift.  For a source redshift of 4, find optical depths of 6e-6 for multiple imaging and 5e-8 for multiplicity of 6 or greater.  Find that extreme magnifications of 100 or more for 6e-9 of z=10 sources with 0.1 kpc radii.  Show some of the image configurations that can be generated by compound lenses, and demonstrate that they are qualitatively different to those generated by single-plane lenses; dedicated compound lens finders will be necessary if these systems are to be discovered in forthcoming surveys.