Day 1029

Tuesday.


1512.06268
Evolution of galaxy shapes from prolate to oblate through compaction events
Tomassetti, Dekel, et al

Study the evolution of global shapes of galaxies using cosmo sims.  The shapes refer to the components of DM, stars and gas at the stellar half-mass radius.  Most galaxies undergo a characteristic compaction event into a blue nugget at z~2-4, which marks the transition from a DM-dominated central body to a self-gravitating baryonic core.  Find that in the high-z, DM-dominated phase, the stellar and DM systems tend to be triaxial, preferentially prolate and mutually aligned.  The elongation is supported by an anisotropic velocity dispersion that originates form the assembly of the galaxy along a dominant large-scale filament.  Estimate that torques by the dominant halo are capable of inducing the elongation of the stellar system and its alignment with the halo.  Then, in association with the transition to self-gravity, small-pericenter orbits puff up and the DM and stellar systems evolve into a more spherical and oblate configuration, aligned with the gas disc and associated with rotation.  This transition typically occurs when the stellar mass is ~1e9 Msun and the escape velocity in the core is ~100 km/s, indicating that SN feedback may be effective in keeping the core DM-dominated and the system prolate.  The early elongated phase itself may be responsible for the compaction event, and the transition to the oblate phase may be associated with the subsequent quenching in the core.


1512.06507
Constraints on the identity of the dark matter from strong gravitational lenses
Li, Frenk, Cole, Gao, Bose, Hellwing

The CDM model unambiguously predicts that a large number of haloes should survive as sub haloes when they are accreted into a larger halo.  The CDM model would be ruled out if such substructures were shown not to exist.  By contrast, if the DM consists of WDM particles, then below a threshold mass that depends on the particle mass far fewer substructures would be present.  Finding sub haloes below a certain mass would then rule out warm particle masses below some value.  Strong gravitational lensing provides a clean method to measure the sub halo mass function through distortions in the structure of Einstein rings and giant arcs.  Using mock lensing observations constructed from high-resolution N-body simulations, show that measurements of approximately 20 strong lens systems with a detection limit of 1e7 Msun/h would clearly distinguish CDM from WDM in the case where this consists of 7 keV sterile neutrinos such as those that might be responsible for the 3.5 keV X-ray emission line recently detected in galaxies and clusters.