• ISM: molecules;
  • galaxies: ISM;
  • radio lines: galaxies


With the observations of the CS (5−4) line towards a sample of 24 infrared bright galaxies using Heinrich Hertz Submillimeter Telescope (HHSMT), we detected CS (5−4) emission in 14 galaxies, including 12 ultraluminous infrared galaxies (ULIRGs)/luminous infrared galaxies (LIRGs) and two nearby normal galaxies. As a good dense gas tracer, which has been well used for studying star formation in the Milky Way, CS (5−4) can trace the active star-forming gas in galaxies. The correlation between CS (5−4) luminosity, which is estimated with detected CS (5−4) line emission, and the infrared luminosity in these 14 galaxies, is fitted with a correlation coefficient of 0.939 and a slope close to unity. This correlation confirms that dense gas, which is closely linked to star formation, is very important for understanding star formation in galaxies.