Day 1316

Tuesday.

1710.00007
A Bayesian hierarchical approach to galaxy-galaxy lensing
Sonnenfeld, Leauthaud

Present a Bayesian hierarchical inference formalism to study the relation between the properties of dark matter haloes and those of their central galaxies using WL.  Unlike traditional methods, this technique does not resort to stacking the WL signal in bins, and thus allows for a more efficient use of the information content in the data.  The method is particularly useful for constraining scaling relations between 2 or more galaxy properties and DM halo mass, and can also be used to constrain the intrinsic scatter in these scaling relations.  Show that, if observational scatter is not properly accounted for, the traditional stacking method can produce biased results when exploring correlations between multiple galaxy properties and halo mass.  For example, this bias can affect studies of the joint correlation between galaxy mass, halo mass, and galaxy size, or galaxy color.  In contrast, the method here easily and efficiently handles the intrinsic and observational scatter in multiple galaxy properties and halo mass.  Test the method on mocks with varying degrees of complexity.  Find that the mean halo mass and concentration can be recovered, each with a 0.1 dex accuracy, and the intrinsic scatter in halo mass with a 0.05 dex accuracy.  In its current version, the method will be most useful for studying the WL signal around central galaxies in groups and clusters, as well as massive galaxies samples with log(M*)>11, which have low satellite fractions.


1710.00434
Origin of the RNA World: the fate of nucleases in warm little ponds
Pearce, et al

Prior to the origin of simple cellular life, the building blocks of RNA (nucleotides) had to form and polymerize in favorable environments on the early Earth.  At this time, meteorites and interplanetary dust particles delivered organics such as nucleases (the characteristic molecules of nucleotides) to warm little ponds whose wet-dry cycles promoted rapid polymerization.  Build a comprehensive numerical model for the evolution of nucleases in warm little ponds leading to the emergence of the first nucleosides and RNA.  Couple Earth's early evolution with complex prebiotic chemistry in these environments.  Find that RNA polymers must have emerged very quickly after the deposition of meteorites (< a few years).  Their constituent nucleases were primarily meteoritic in origin and not from interplanetary dust particles.  Ponds appeared as contents rose out of the early global ocean but this increasing availability of "targets" for meteorites was offset by declining meteorite bombardment rates.  Moreover, the rapid losses of nucleases to pond seepage during wet periods, and to UV photodissociation during dry periods means that the synthesis of nucleotides and their polymerization into RNA occurred in just one of the few wet-dry cycles.  Under these conditions, RNA polymers likely appeared prior to 4.17 B years ago.  Significance: There are 2 competing hypothesis for the site at which an RNA world emerged: hydrothermal vents in the deep ocean and warm little ponds.  Because the former lacks wet and dry cycles, which are all known to promote polymerization (in this case, of nucleotides into RNA), construct a comprehensive model for the origin of RNA in the latter sites.  The model advances the story and timeline of the RNA world by constraining the source of biomolecules, the environmental conditions, the timescales of reaction, and the emergence of first RNA polymers.