Day 1733

Tuesday.

2007.05579

One, no one, and one hundred thousand -- inferring the properties of a population in presence of selection effects

Vitale

This document contains a pedagogical introduction to hierarchical Bayesian inference in presence of selection effects. The main equations are obtained from first principles, step by step. Two examples are provided which show how things work, in practice. While I had in mind gravitational-wave astrophysics as I drafted these notes, they should be generic enough to be useful to anyone who wants to learn about the inference on the properties of a population of sources.

2007.05603

Geometric support for dark matter by an unaligned Einstein Ring in Abell 2837

Chen, Broadhurst, et al

The non-detection of dark matter (DM) particles in increasingly stringent laboratory searches has encouraged alternative gravity theories where gravity is sourced only from visible matter. Here, we consider whether such theories can pass a two-dimensional test posed by gravitational lensing -- to reproduce a particularly detailed Einstein ring in the core of the galaxy cluster Abell 3827. We find that when we require the lensing mass distribution to strictly follow the shape (ellipticity and position angle) of the light distribution of cluster member galaxies, intracluster stars, and the X-ray emitting intracluster medium, we cannot reproduce the Einstein ring, despite allowing the mass-to-light ratios of these visible components to freely vary with radius to mimic alternative gravity theories. Alternatively, we show that the detailed features of the Einstein ring are accurately reproduced by allowing a smooth, freely oriented DM halo in the lens model, with relatively small contributions from the visible components at a level consistent with their observed brightnesses. This dominant DM component is constrained to have the same orientation as the light from the intracluster stars, indicating that the intracluster stars trace the gravitational potential of this component. The Einstein ring of Abell 3827 therefore presents a new challenge for alternative gravity theories: not only must such theories find agreement between the total lensing mass and visible mass, but they must also find agreement between the projected sky distribution of the lensing mass and that of the visible matter, a more stringent test than has hitherto been posed by lensing data.

2007.05736

Synchronized neutrino communications over intergalactic distances

Santos, Fischbach, Gruenwald

We discuss how high energy neutrino communications could be synchronized to large-scale astrophysical events either in addition to or instead of electromagnetic signals.