Non-parametric Morphologies of Mergers in the Illustris Simulation

BIGNONE, LUCAS; TISSERA, PATRICIA; SILLERO, E.; PEDROSA, SUSANA; PELLIZZA, L.; GARCÍA LAMBAS, D.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017 vol. 465

0035-8711

We study non-parametric morphologies of mergers events in a cosmological context,using the Illustris project. We produce mock g-band images comparable to observationalsurveys from the publicly available Illustris simulation idealized mock imagesat z = 0. We then measure non parametric indicators: asymmetry, Gini, M20, clumpinessand concentration for a set of galaxies with M∗ > 1010 M⊙. We correlate theseautomatic statistics with the recent merger history of galaxies and with the presenceof close companions. Our main contribution is to assess in a cosmological framework,the empirically derived non-parametric demarcation line and average time-scales usedto determine the merger rate observationally. We found that 98 per cent of galaxiesabove the demarcation line have a close companion or have experienced a recentmerger event. On average, merger signatures obtained from the G − M20 criteria anticorrelateclearly with the elapsing time to the last merger event. We also find thatthe asymmetry correlates with galaxy pair separation and relative velocity, exhibitingthe larger enhancements for those systems with pair separations d < 50 h−1 kpc andrelative velocities V < 350 km s−1. We find that the G − M20 is most sensitive torecent mergers (∼ 0.14 Gyr) and to ongoing mergers with stellar mass ratios greaterthan 0.1. For this indicator, we compute a merger average observability time-scale of∼ 0.2 Gyr, in agreement with previous results and demonstrate that the morphologicallyderived merger rate recovers the intrinsic total merger rate of the simulation andthe merger rate as a function of stellar mass.