Day 888

Tuesday.


1505.04429
Effects of hot halo gas on the star formation and mass transfer during distant galaxy-galaxy encounters
Hwang, Park

Use N-body/SPH sims of encounters between an ETG and a LTG to study the effects of hot halo gas on the evolution for a case with the mass ratio of the ETG to LTG of 2:1 and the closest approach distance of ~100 kpc.  Find that the dynamics of the cold disk gas in the tidal bridge and the amount of the newly formed stars depend strongly on the existence of a gas halo.  In the run of interacting galaxies not having a hot gas halo, the gas and stars accreted into the ETG do not include newly formed stars.  However, in the run using the ETG wit ha gas halo and the LTG without a gas halo, a shock forms along the disk gas tidal bridge and induces SF near the closest approach.  The shock front is parallel to a channel along which the cold gas flows toward the center of the ETG.  As a result, the ETG can accrete SF cold gas and newly born stars at an near its center.  When both galaxies have hot gas halos, a shock is formed between the two gas halos somewhat before the closest approach.  The shock hinders the growth of the cold gas bridge to the ETG and also ionizes it.  Only some of the disk stars transfer through the stellar bridge.  Conclude that the hot halo gas can give significant hydrodynamic effects during distant encounters.


1505.04758
The sudden appearance of dust in the early Universe
Mattsson

Observations suggest that high-z galaxies are either very dusty or essentially dust free.  The evolution from one regime to the other must also be very fast, since evolved and dusty galaxies show up at z corresponding to a Universe which is only about 500 Myr old.  In the present paper models which predicts the existence of an apparent dichotomy between dusty and dust-free galaxies at high z are considered.  Galaxies become dusty as soon as they reach an evolved state and the transition is very rapid.  A special case suggests that while stellar dust production is overall relatively insignificant -- contrary to what has been argued recently -- it can at the same time be consistent with efficient dust production in SNe in the local Universe.  Special attention will be given to the recent discovery of a dusty normal galaxy (A1689-zD1) at a very high z=7.5±0.2.