Day 654

Monday.

1405.2070
Intra-cluster light at the frontier: Abell 2744
Montes, Trujillo

The ultra-deep multi wavelength HST Frontier Fields coverage of the Abell Cluster 2744 is used to derive the stellar population properties of its ICL.  The rest frame colors of the ICL of this intermediate redshift (z=0.3064) massive cluster are bluer (g-r~0.7, i-J~0.6) than those found in the stellar populations of its main galaxy members (g-r~0.85; i-J~0.75).  Based on these colors, derive the following mean metallicity Z~0.018pm0.003 for the ICL.  The ICL age is ~3-5 Gyr younger than the average age of the massive galaxies of the cluster.  The fraction of stellar mass in the ICL component comprises at least 6% of the total stellar mass of the galaxy cluster.  Data is consistent with a scenario where the bulk of the ICL of Abell 2744 has been formed relatively recently (z<1).  The stellar population properties of the ICL suggest that this diffuse component is mainly the result of the disruption of infalling galaxies with similar characteristics in mass (M*~3e10 Msun) and metallicity than the MW.

1405.2072
Missing black holes in brightest cluster galaxies as evidence for the occurrence of super kicks in nature
Gerosa, Sesana

SMBH can be kicked out because of the asymmetric gravitational wave emission (during a merger event) with kicks as large as ~5000 km/s, pushing the SMBHs out in the cluster outskirts for a time comparable to galaxy-evolution timescales.  Measurements of SMBH occupation fraction can be used to observationally test the existence of super kicks in nature; BCGs are the ideal objects to explore this possibility.  A single observational confirmation of a missing nuclear SMBH would provide strong evidence for the occurrence of super kicks in the strong-gravity regime of BH mergers.