Day 1318

Thursday.

1710.01303
Cosmic shear with Einstein Rings
Birrer, Referier, Amara

Explore a new technique to measure cosmic shear using Einstein rings as standard shapes.  Einstein rings are formed the a strong lensing system has circular symmetry.  These rings can become elliptical due to WL by foreground structures.  Birrer+(2017) showed that the detailed modeling of Einstein rings can be used to measure external shear to high precision.  In this letter, explore how a collection of Einstein rings can be used as a statistical probe of cosmic shear.  Present a forecast of the cosmic shear information available in Einstein rings for different strong lensing survey configurations.  Find that, assuming that the number density of Einstein rings in the COSMOS survey is representative, future strong lensing surveys should have a cosmological precision comparable to the current ground based WL surveys.  Discuss how this technique is complementary to the standard cosmic shear analyses since it is sensitive to different systematic and can be used for cross-calibration.


1710.01314
The Herschel Space Observatory has revealed a very different galaxyscape from that shown by optical surveys which presents a challenge for galaxy-evolution models.  The Herschel surveys reveal (1) that there was rapid galaxy evolution in the very recent past and (2) that galaxies lie on a single Galaxy Sequence (GS) rather than a star-forming `main sequence' and a separate region of `passive' or `red-and-dead' galaxies.  The form of the GS is now clearer because FIR surveys such as the Herschel ATLAS pick up a population of optically-red SF galaxies that would have been classified as passive using most optical criteria.  The space-density of this population is at least as high as the traditional SF population.  By stacking spectra of H-ATLAS galaxies over the range 0.001<z<0.4, show that the galaxies responsible for the rapid low-z evolution have high stellar masses, high SF rates but, even several billion years in the past, old stellar populations - they are thus likely to be relatively recent ancestors of early-type galaxies in the Universe today.  The form of the GS is inconsistent with rapid quenching models and neither the analytic bathtub model nor the hydrodynamical EAGLE simulation can reproduce the rapid cosmic evolution.  Propose a new gentler model of galaxy evolution that can explain the new Herschel results and other key properties of the galaxy population.