Timescales for the Effects of Interactions on Galaxy Properties and SMBH Growth

• DOI: 10.1093/mnras/staf541
• Publication Date: 2025-04-04T04:49:23Z
• Authors: David O’Ryan; Brooke D Simmons; Andreas L Faisst; Izzy L Garland; Tobias Géron; Ghassem Gozaliasl; Steven Gillman; Sofia Guedes Vaz ...; William C Keel; Anton M Koekemoer; Sandor Kruk; Karen L Masters; Montoya C Oscar; Mason Redden; Matthew R Thorne; Emily R Walls; Deneth Weerasinghe; John R Weaver

Abstract Galaxy interaction and merging have clear effects on the systems involved. We find an increase in the star formation rate (SFR), potential ignition of active galactic nuclei (AGN) and significant morphology changes. However, at what stage during interactions or mergers these changes begin to occur remains an open question. With a combination of machine learning and visual classification, we select a sample of 3,162 interacting and merging galaxies in the Cosmic Evolutionary Survey (COSMOS) field across a redshift range of 0.0 - 1.2. We divide this sample into four distinct stages of interaction based on their morphology, each stage representing a different phase of the dynamical timescale. We use the rich ancillary data available in COSMOS to probe the relation between interaction stage, stellar mass, SFR, and AGN fraction. We find that the distribution of SFRs rapidly change with stage for mass distributions consistent with being drawn from the same parent sample. This is driven by a decrease in the fraction of red sequence galaxies (from 17 % as close pairs to 1.4 % during merging) and an increase in the fraction of starburst galaxies (from 7 % to 32 %). We find the AGN fraction increases by a factor of 1.2 only at coalescence. We find the effects of interaction peak at the point of closest approach and coalescence of the two systems. We show that the point in time of the underlying dynamical timescale - and its related morphology - is as important to consider as its projected separation.