Progress of the Study on (Sub)millimeter Lines in Galaxies During the Herschel Period

Abstract

After the advent of Herschel Space Observatory, there is much progress of the observational studies on the (sub)millimeter ((sub)mm) lines, such as the middle to high-J CO rotational transitions (J= 4–10), multiple H2O lines, and fine-structure emissions of atoms (e.g., C, O) and ions (e.g., C+, N+). These lines are important coolants for the interstellar medium (ISM), and thus can be used to investigate the physical conditions and chemical compositions of the ISM, as well as their power sources. In this paper, we first introduce how to investigate the star formation properties (such as the calibration of star formation rate (SFR) and the determination of star formation mode) using different (sub)mm lines. Then we review for the different methods of measuring total molecular mass, and discuss their advantages and caveats. At last we summarize the use of CO (CO spectral line energy distribution (CO SLED) and the ratio of mid-J CO lines to far-infrared continuum) and other lines to diagnose the power source in galaxies.