Day 1214

Wednesday.

1702.01921
Pure iron grains are rare in the universe
Kimura, et al

The abundant forms in which the major elements in the universe exist have been determined from numerous astronomical observations and meteoritic analyses.  Fe is an exception, in that only depletion of gaseous Fe has been detected in the ISM, suggesting that Fe is condensed into a solid, possibly the astronomical invisible metal.  To determine the primary form of Fe replicate the formation of Fe grains in gaseous ejecta of evolved stars by means of microgravity experiments.  Find that the sticking probability for formation of Fe grains is extremely small; only several atoms will stick per hundred thousand collisions, so that homogeneous nucleation of metallic Fe grains is highly ineffective, even in the Fe-rich ejecta of SNe Ia.  This implies that most Fe is locked up as grains of Fe compounds or as impurities accreted onto other grains in the ISM.


1702.02064
The separate and combined effects of baryon physics and neutrino free-streaming on large-scale structure
Mummery, et al

Use the cosmo-OWLS and BAHAMAS suites of cosmo hydro sims to explore the separate and combined effects of baryon physics (particularly feedback from AGN) and free-streaming of massive neutrinos on LSS.  Focus on 5 diagnostics: i) the halo mass function, ii) halo mass density profiles, iii) the halo mass-concentration relation, iv) the clustering of haloes, and v) the clustering of matter; and explore the extent to which the effects of baryon physics and neutrino free-streaming can be treated independently.    Consistent with previous studies, find that both AGN feedback and neutrino free-streaming suppress the total matter power spectrum, although their scale and redshift dependences differ significantly.  The inclusion of AGN feedback can significantly reduce the masses of groups and clusters, and increase their scale radii.  These effects lead to a decrease in the amplitude of the mass-concentration relation and an increase in the halo autocorrelation function at fixed mass.  Neutrinos also lower the masses of groups and clusters while having no significant effect on the shape of their density profiles (thus also affecting the mass-concentration relation and halo clustering in a qualitatively similar way to feedback).  Show that, with only a small number of exceptions, the combined effects of baryon physics and neutrino free-streaming on all 5 diagnostics can be estimated to typically better than a few percent accuracy by reading these processes independently (i.e. by multiplying their separate effects).