Can we judge the efficiency of star formation by galaxy morphologies?
Galaxy morphologies are very diverse - some galaxies have spiral disks, while some other galaxies have elliptical morphologies with stellar spheroids. It is well known that galaxy morphologies are tightly correlated with their star formation activity. However, the origin of their correlation is still unclear. As a responsible scenario for the correlation, recent simulations predict that the efficiency of star formation in elliptical galaxies is lower than that in disk galaxies, so called "morphological quenching" scenario. To observationally test this scenario, we focused on the green valley galaxies. They are a transient population between star forming galaxies and passive galaxies and have a wide variety of morphologies, hence they are ideally suited for studying the effect of morphologies on their star formation activity. In this study, we investigated the relation between galaxy morphologies and star formation efficiencies on the basis of our CO line observations of disk- and bulge-dominated green valley galaxies with the Nobeyama 45m radio telescope. Our observation revealed that the star formation efficiency for the green valley galaxies does not change with their morphologies. Our result suggests little impact of galaxy morphologies on their star formation process in contrast to the prediction of the morphological quenching scenario. These observation results were published as Koyama et al. “Can we judge the efficiency of star formation by galaxy morphologies?”(doi: 10.3847/1538-4357/ab0e75) in the Astrophysical Journal on April 2, 2019.
- Figure. A schematic diagram of this study. In this study, we selected the green valley galaxies with disk- and bulge-dominated morphologies, and compared their star formation efficiencies on the basis of our CO line observations with the NRO45m. Upper and lower panels show the SDSS images of the galaxies and the CO spectra obtained by our NRO45m observations, respectively.