Oral Presentation

Relation between molecular gas and star-forming activity on the merger sequence in local U/LIRGs

Author(s): Akino Yasuda (The University of Tokyo), Kentaro Motohara (NAOJ), Shuhei Koyama (The University of Tokyo)

Presenter: Akino Yasuda (The University of Tokyo)

Previous studies have shown that there is a strong correlation between the stellar mass and star formation rate (SFR) in galaxies, called the star formation main sequence (SFMS). Galaxies located above the SFMS in the SFR – stellar mass plane are particularly active in star formation and are called luminous infrared galaxies (LIRGs) or ultra-luminous infrared galaxies (ULIRGs) based on their infrared emission. One of the causes of active star formation in U/LIRGs is thought to be the interaction between galaxies, and many U/LIRGs are known to interact with each other. Studying these active star-forming activities is important for understanding galaxy formation and evolution. To understand the physics behind the active star formation of U/LIRGs, we estimated the molecular gas masses of 45 local U/LIRGs using 12CO (1-0) line data observed by the Nobeyama 45 m radio telescope. These sources (PARADISES galaxies) were selected from the sample of the PARADISES project, a near-infrared narrow-band imaging survey of the Pa α emission lines of local U/LIRGs. Molecular gas masses of PARADISES galaxies and samples from two previous studies were examined in relation to molecular gas mass, molecular gas fraction, star formation efficiency, and galaxy properties. In order to investigate the relationship between interactions and star formation activity in local U/LIRGs, the objects in our sample were classified into merger stages based on their morphology. The results show no trend in molecular gas fraction or star formation efficiency with merger stage in PARADISES galaxies.