Environmental Quenching in the SAMI Galaxy Survey and Hydrodynamical Simulations

Abstract

In this thesis, we investigate the mechanisms that quench star formation in all environments and how fast the quenching processes happen, especially in dense regions like groups and clusters. We have utilized the full sample from the SAMI Galaxy Survey, the EAGLE/C-EAGLE hydrodynamical simulation results from z=0 to z=2, as well as the environmental metric and broadband photometric data from the GAMA catalogue.

Firstly, we identify galaxies that are currently undergoing quenching processes with the spatially-resolved star formation distribution by using a star-formation concentration index (C-index). Denser environments have a higher fraction of galaxies with low C-index, indicating "outside-in" quenching due to ram pressure-stripping. However, at z > 1, quenching in simulations shows no clear "outside-in" signatures, limiting the C-index's use as a quenching proxy.

Secondly, we investigate the physical properties influencing "outside-in" quenching in groups and clusters. Using the SAMI observational data, we find the formation of SF-concentrated galaxies is primarily influenced by the overall cluster environment rather than nearby galaxy interactions or local environments. Additionally, using infall timescale and orbital information from the Eagle simulations, we find that environmental quenching is more related to the closest approach radius and the duration of a galaxy's satellite phase, rather than its current position in groups or clusters.

Lastly, we estimate quenching timescales for SF-concentrated galaxies. By analyzing the SAMI radial age profiles, high-mass group SF-concentrated galaxies have older ages in their outer discs (1-2 R_e) compared to ungrouped regular galaxies, with an age difference of ~2 Gyr. SED fitting with Bagpipes and SAMI data reveals faster quenching timescales in higher mass groups. Eagle simulations demonstrate slower quenching timescales (> 2 Gyr) at z=0 and more rapid quenching (< 2 Gyr) at higher redshifts (z > 1).