Oral Presentation

Mergers, Star Formation, and AGN activity in the HSC-SSP - a Cautionary Tale

Author(s): Kiyoaki Christopher Omori (Saint Mary's University), Connor Bottrell (UWA), Sabine Bellstedt (UWA), Aaron S. G. Robotham (UWA), Hassen M. Yesuf (Shanghai Astronomical Observatory), Andy D. Goulding (Princeton University), Marcin Sawicki (Saint Mary's University), Tohru Nagao (Ehime University), Tsutomu T. Takeuchi (Nagoya University)

Presenter: Kiyoaki Omori (Saint Mary's University)

In the currently accepted cosmological framework, galaxies are considered to evolve through merger activity. Galaxy mergers are associated are strongly tied with processes pertaining to galaxy evolution, such as enhancement of star formation and active galactic nuclei (AGN) activity, making them an important lab to study galaxy evolution. However, quantitative conclusions on the relative role of galaxy interactions and mergers on star formation and AGN activity is still unclear. In this work, we investigate the connection between mergers, star formation, and AGN activity in HSC-SSP galaxies. We first identify merger candidates using a deep representation learning-based method, where we fine-tune the pre-trained model Zoobot (Walmsley et al. 2023) using observational HSC-SSP images, and further visually purify the sample into close pairs and post-mergers. Using our merger samples, we investigate whether an enhancement in star formation and AGN activity exists within mergers relative to their controls, using galaxy properties based on the results of the full SED fitting code PROSPECT (Robotham et al. 2020, Thorne et al. 2022). We find that there is little enhancement in star formation activity among our merger samples. For AGN activity, we find enhancement only in the post-merger stage. These results present a cautionary tale when conducting merger studies, in particular with sample selection and the timescale of galaxy physical properties. We discuss our results.