Day 1504

Wednesday.

1811.10604

Astrophyiscs with radioactive isotopes

Diehl

Radioactivity was discovered as a by-product of searching for elements with suitable chemical properties.  Understanding its characteristics led to the development of nuclear physics, understanding that unstable configurations of nucleons transform into stable end products through radioactive decay.  In the universe, nuclear reactions create new nuclei under the energetic circumstances characterizing cosmic nucleosynthesis sites, such as the cores of stars and SN explosions.  Observing the radioactive decays of unstable nuclei which are by-products of such cosmic nucleosynthesis, is a special discipline of astronomy.  Understanding these special cosmic sites, their environments, their dynamics, and their physical processes, is the 'Astrophysics with Radioactivities' that makes the subject of this book.  Address the history, the candidate sites of nucleosynthesis, the different observational opportunities, and the tools of this field of astrophysics.


1811.10607
Formation of ultra-diffuse galaxies in the field and in galaxy groups
Jian, Dekel, et al

Study UDGs in zoom in cosmo sims, seeing the origins of UDGs in the field versus galaxy groups.  Find that while field UDGs arise from dwarfs in a characteristic mass range by multiple episodes of SN feedback, group UDGs may also form by tidal puffing up and they become quiescent by ram-pressure stripping.  The field and group UDGs share similar properties, independent of distance from the group centre.  Their DM haloes have ordinary spin parameters and centrally dominant DM cores.  Their stellar component tend to have a prolate shape with a Sersic index n~1 but no significant rotation.  Ram pressure removes the gas from the group UDGs when they are at pericentre, quenching SF in them and making them redder.  This generates a color/SFR gradient with distance from the center, as observed in clusters.  Find that ~20% of the field UDGs that fall into a massive halo survive as satellite UDGs.  In addition, normal field dwarfs on highly eccentric orbits can become UDGs near pericentre due to tidal puffing up, contributing about half of the group-UDG pupation.  Interpret the findings using simple toy models, showing that gas stripping is mostly due to ram pressure than tides.  Estimate that the energy deposited by tides in the bound component of a satellite over one orbit can cause significant puffing up provided that the orbit is sufficiently eccentric.