The molecular gas mass is the fundamental parameter to understand star formation processes in galaxies. The emission line from carbon monoxide (CO) has been used as the traditional method to measure molecular gas mass in galaxies. Recently, the modern method using the atomic carbon emission line ([CI]) has been proposed in order to estimate the molecular gas mass in high-z galaxies. In order to establish the modern [C I] method, it is necessary to check the consistency with the traditional CO method. In this my project, through our own [CI] and CO survey of nearby luminous infrared galaxies using Atacama Millimeter/submillimeter Array (ALMA), the modern [C I] and the traditional CO methods are directly compared. Our latest observations discover the [CI]-poor, CO-rich galaxies that have not been identified in previous projects, providing instructions for the use of the modern [CI] methods.
I present survey results of CO J=1–0 for 10 type 1 active galactic nuclei (AGNs) at z~0.3 based on observations at the Nobeyama Radio Observatory. No significant CO J=1–0 emission lines were confirmed in any targets. The upper limits of CO J=1–0 luminosities are lower than expected given the molecular gas mass inferred from nebular dust extinction. This inconsistency between molecular gas mass indicated by CO J=1–0) and optical measurements suggests that the dust with high column density contributing to the majority of the extinction may not trace diffuse cold gas associated with host galaxies in the case of our observed AGNs.