Non-parametric Morphologies of Mergers in the Illustris Simulation

BIGNONE, L.A.; TISSERA, P.B.; SILLERO, E.; PEDROSA, S.E.; PELLIZZA, L.J.; LAMBAS, D.G.

Santiago

Workshop; Second Chilean Workshop on Theoretical and Numerical Astrophysics; 2016

We study non-parametric morphologies of mergers events in a cosmological context, usingthe Illustris project. We produce mock g-band images comparable to observational surveysfrom the publicly available Illustris simulation idealized mock images at z = 0. We thenmeasure non-parametric indicators: asymmetry, Gini, M 20 , clumpiness, and concentration fora set of galaxies with M ∗ > 10 10 M . We correlate these automatic statistics with the recentmerger history of galaxies and with the presence of close companions. Our main contributionis to assess in a cosmological framework, the empirically derived non-parametric demarcationline and average time-scales used to determine the merger rate observationally. We foundthat 98 per cent of galaxies above the demarcation line have a close companion or haveexperienced a recent merger event. On average, merger signatures obtained from the G–M 20criterion anti-correlate clearly with the elapsing time to the last merger event. We also find thatthe asymmetry correlates with galaxy pair separation and relative velocity, exhibiting the largerenhancements for those systems with pair separations d < 50 h −1 kpc and relative velocitiesV < 350 km s −1 . We find that the G–M 20 is most sensitive to recent mergers (∼0.14 Gyr) andto ongoing mergers with stellar mass ratios greater than 0.1. For this indicator, we compute amerger average observability time-scale of ∼0.2 Gyr, in agreement with previous results anddemonstrate that the morphologically derived merger rate recovers the intrinsic total mergerrate of the simulation and the merger rate as a function of stellar mass.