Day 1136

Tuesday.

1608.03892
Major mergers are not significant drivers of star formation or morphological transformation around the epoch of peak cosmic star formation
Lofthouse, Kaviraj, Conselice, Mortlock, Hartley

Investigate the contribution of major mergers (mass ratios > 1:5) to stellar mass growth and morphological transformations around the epoch of peak cosmic star formation (z~2).  Visually classify a complete sample of massive (M>1e10 Msun) galaxies at this epoch, drawn from the CANDELS survey, into late-type galaxies, major mergers, spheroids and disturbed spheroids which show morphological disturbances.  Given recent sim work, which indicates that recent (<0.3-0.4 Gyr) major-merger remnants exhibit clear tidal features in such images, use the fraction of disturbed spheroids to probe the role of major mergers in driving morphological transformations.  The percentage of blue spheroids (i.e. with ongoing star formation) that show morphological disturbances is only 21±4%, indicating that major mergers are not the dominant mechanism for spheroid creation at z~2 --- other processes, such as minor mergers or cold accretion are likely to be the main drivers of this process.  Also use the rest-frame U-band luminosity as a proxy for star formation to show that only a small fraction of the star formation budget (~3%) is triggered by major mergers.  Take together, the results show that major mergers are not significant drivers of galaxy evolution at z~2.


1608.03926
The Moon as a recorder of nearby supernovae
Crawford

The lunar geological record is expected to contain a rich record of the galactic environment of the Solar System, including records of nearby (i.e. less than a few tens of parsecs) SN explosions.  This record will be composed of 2 principal components: (i) cosmogenic nuclei produced within, as well as radiation damage to, surface materials caused by increases in the galactic CR flux resulting from nearby SNe; and (ii) the direct collection of SN ejecta, likely enriched in a range of unusual and diagsnotic isotopes, on the lunar surface.  Both aspects of this potentially very valuable astrophysical archive will be best preserved in currently buried, but nevertheless near-surface, layers that were directly exposed to the space environment at known times in the past and for known durations. Suitable geological formation certainly exist on the Moon, but accessing them will require a greatly expanded program of lunar exploration.