Day 1327

Friday.

1710.09465
Parameter constraints from cross-correlation of CMB lensing with galaxy clustering
Schmittfull, Seljak

The lensing convergence measurable with future CMB surveys like CMB-S4 will be highly correlated with the clustering observed by deep photometric LSS surveys such as the LSST, with cross-correlation coefficient as high as 95%.  This will enable use of sample variance cancellation techniques to determine cosmological parameters, and use of cross-correlation measurements to break parameter degeneracies.  Assuming large sky overlap between CMB-S4 and LSST, show that a joint analysis of CMB-S4 lensing and LSST clustering can yield very tight constraints on the matter amplitude sigma8(z), halo bias, and f_NL, competitive with the best stage IV experiment predictions, but using complementary methods, which may carry different and possibly lower systematics.  Having no sky overlap between experiments degrades the precision of sigma8(z) by a factor of 20, and that of f_NL by a factor of 1.5 to 2.  Without CMB lensing, the precision always degrades by an order of magnitude or more, showing that a joint analysis is critical.  The results also suggest that CMB lensing in combination with LSS photomtetric surveys is a competitive probe of the evolution of structure in the range z~1-7, probing a regime that is not well tested observationally.  Explore predictions against other surveys and experiment configurations, finding that wide patches with maximal sky overlap between CMB and LSS surveys are most powerful for sigma8(z) and f_NL.


1710.09573
Time resolved 2 million year old supernova activity discovered in Earth's microfossil record
Ludwig, et al

Massive stars, which terminate their evolution as core collapse supernovae, are theoretically predicted to eject more than 1e-5 Msun of the radioisotope 60Fe.  If such an event occurs sufficiently close to the solar system, traces of the supernova debris could be deposited on Earth.  Report a time resolved 60Fe signal residing, at least partially, in a biogenic reservoir.  Using accelerator mass spectrometry, this signal was found through the direct detection of live 60Fe atoms contained within secondary iron oxides, among which are magnetofossils, the fossilized chains of magnitite crystals produced by magnetotactic bacteria.  The magnetofossiles were chemically extracted from two Pasific Ocean sediment drill cores.  The results show that the 60Fe signal onset occurs around 2.6 Ma to 2.8 Ma, near the lower Pleistocene boundary, terminates around 1.7 Ma, and peaks at about 2.2 Ma.