Day 871

Tuesday.


1504.04623
Cosmological tests of gravity
Koyama

Einstein's GR is tested accurately within the local universe (SS), but this leaves open the possibility that it is not a good description at the largest scales in the Universe.  The standard model of cosmology assumes GR as the theory to describe gravity on all scales.  In 1998, astronomers made the discovery that the expansion of the Universe is accelerating, not slowing down.  This late-time acceleration of the Universe has become the most challenging problem in theoretical physics.  Within the framework of GR, the acceleration would originate from an unknown DE.  Alternatively, it could be that there is no DE and GR itself is in error on cosmological scales.  The standard model of cosmology is based on a huge extrapolation of the limited knowledge of gravity.  This discovery of the late time acceleration of the Universe may require a revision of the theory of gravity and the standard model of cosmology based on GR.  Review recent progress in constructing modified gravity model as an alternative to DE and developing cosmological tests of gravity.


1504.04988
Formation of elongated galaxies with low masses at high redshift
Ceverino, Primack, Dekel

Report the identification of elongated (triaxial or prolate) galaxies in cosmological sims at z~2. These are preferentially low-mass galaxies (M_s<1e9.5 Msun), residing in DM haloes with strongly elongated inner parts, a common feature of high-z DM haloes in the LCDM cosmology.  Feedback slows formation of stars at the centers of these haloes, so that a dominant and prolate DM distribution gives rise to galaxies elongated along the DM major axis.  As galaxies grow in stellar mass, stars dominate the total mass within the galaxy half-mass radius, making stars and DM rounder and more oblate.  A large population of elongated galaxies produces a very asymmetric distribution of projected axis ratios, as observed in high-z galaxy surveys.  This indicates that the majority of the galaxies at high z are not discs or spheroids but rather galaxies with elongated morphologies.