Day 1005

Wednesday.


1511.02854
Possible group origins VII. Galaxy substructures in fossil systems
Aarattani, et al

Fossil groups are expected to be the final product of galaxy merging within galaxy groups.  In simulations, they are predicted to assemble their mass at high redshift.   This early formation allows for the innermost M* galaxies to merge into a massive central galaxy.  Then, they are expected to maintain their fossil status because of the few interactions within the LSS.  In this context, the magnitude gap between the two brightness galaxies o f the system is considered a good indicator of its dynamical status.  As a consequence, the systems with the largest gaps should be dynamically relaxed.  In order to examine the dynamical status of these systems, systematically analyze the presence of galaxy substructures in a sample of 12 spectroscopically-confirmed fossil systems with 2d space of projected positions out to R200.   Moreover, for a subsample of 5 systems with at least 30 spec-confirmed members, analyze the substructure in the velocity and in the 3-d velocity-position spaces.  Additionally, look for signs of recent mergers in the regions around the central galaxies.  Find that an important fraction of fossil systems show substructure.  The fraction depends critically on the adopted test, since each test is more sensible to a particular type of substructure.  The interpretation of the results is that fossil systems are not, in general, as relaxed as expected from simulations.  The sample of 12 spec-confirmed fossils systems need to be extended in order to compute an accurate nation, but the conclusion is that this is similar to the fraction of substructure detected in non-fossil clusters.


1511.02862
Satellite quenching and galactic conformity at 0.3<z<2.5
Kawinwanichakij, et al

Measure the evolution of the quiescent fraction and quenching efficiency of satellites around SF and quiescent central galaxies with stellar mass log (Mcen/Msun)>10.5 at 0.3<z<2.5.  combine imaging from 3 deep NIR selected surveys (ZFOURGE/CANDELS, UDS, and UltraVISTA), which allows us to select a stellar-mass complete sample of satellites with log (Msat/Msun)>9.3.  Satellites for both SF and quiescent central galaxies have higher quiescent fractions compared to field galaxies matched in stellar mass at all redshifts.  Also observe "galactic conformity": satellites around quiescent centrals are more likely to be quenched compared to the satellites around SF centrals.  In the sample, this conformity signal is significant at >3 sigma for 0.6<z<1.6, whereas it is only weakly significant at 0.3<0.6 and 1.6<z<2.5  Therefore, conformity (and therefore satellite quenching) has been present for a significant fraction of the age of the universe.  The satellite quenching efficiency increases with increasing stellar mass of the central, but does not appear to depend on the stellar mass of the satellite to the mass limit of the sample.  When comparing the satellite quenching efficiency of SF centrals with stellar masses 0.2 dex higher than quiescent centrals (which should account for any difference in halo mass), the conformity signal decreases, but remains statistically significant at 0.6<z<0.9.  This is evidence that satellite quenching is connected to the SF properties of the central as well as to the mass of the halo.  Discuss physical effects that may contribute to galactic conformity, and emphasize that they must allow for continued SF in the central galaxy even as the satellites are quenched.